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![Peter Zijlstra](/assets/img/avatar_default.png)
Perf fuzzer gifted a lockdep splat:
perf_event_init_context()
mutex_lock(parent_ctx->mutex); (B)
inherit_task_group()
inherit_group()
inherit_event()
perf_event_alloc()
perf_try_init_event() := hw_breakpoint_event_init()
register_perf_hw_breakpoint()
mutex_lock(child->perf_event_mutex); (A)
Which is against the normal (documented) order. Now, this is a false
positive in that child is not published yet, but also inherited events
never end up on ->perf_event_list.
Annotate this one away.
Fixes: 0912037fec
("perf/hw_breakpoint: Reduce contention with large number of tasks")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
1051 lines
27 KiB
C
1051 lines
27 KiB
C
// SPDX-License-Identifier: GPL-2.0+
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/*
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* Copyright (C) 2007 Alan Stern
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* Copyright (C) IBM Corporation, 2009
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* Copyright (C) 2009, Frederic Weisbecker <fweisbec@gmail.com>
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*
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* Thanks to Ingo Molnar for his many suggestions.
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*
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* Authors: Alan Stern <stern@rowland.harvard.edu>
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* K.Prasad <prasad@linux.vnet.ibm.com>
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* Frederic Weisbecker <fweisbec@gmail.com>
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*/
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/*
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* HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
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* using the CPU's debug registers.
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* This file contains the arch-independent routines.
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*/
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#include <linux/hw_breakpoint.h>
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#include <linux/atomic.h>
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#include <linux/bug.h>
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#include <linux/cpu.h>
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#include <linux/export.h>
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#include <linux/init.h>
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#include <linux/irqflags.h>
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#include <linux/kdebug.h>
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#include <linux/kernel.h>
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#include <linux/mutex.h>
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#include <linux/notifier.h>
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#include <linux/percpu-rwsem.h>
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#include <linux/percpu.h>
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#include <linux/rhashtable.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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/*
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* Datastructure to track the total uses of N slots across tasks or CPUs;
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* bp_slots_histogram::count[N] is the number of assigned N+1 breakpoint slots.
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*/
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struct bp_slots_histogram {
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#ifdef hw_breakpoint_slots
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atomic_t count[hw_breakpoint_slots(0)];
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#else
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atomic_t *count;
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#endif
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};
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/*
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* Per-CPU constraints data.
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*/
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struct bp_cpuinfo {
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/* Number of pinned CPU breakpoints in a CPU. */
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unsigned int cpu_pinned;
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/* Histogram of pinned task breakpoints in a CPU. */
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struct bp_slots_histogram tsk_pinned;
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};
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static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]);
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static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type)
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{
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return per_cpu_ptr(bp_cpuinfo + type, cpu);
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}
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/* Number of pinned CPU breakpoints globally. */
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static struct bp_slots_histogram cpu_pinned[TYPE_MAX];
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/* Number of pinned CPU-independent task breakpoints. */
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static struct bp_slots_histogram tsk_pinned_all[TYPE_MAX];
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/* Keep track of the breakpoints attached to tasks */
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static struct rhltable task_bps_ht;
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static const struct rhashtable_params task_bps_ht_params = {
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.head_offset = offsetof(struct hw_perf_event, bp_list),
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.key_offset = offsetof(struct hw_perf_event, target),
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.key_len = sizeof_field(struct hw_perf_event, target),
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.automatic_shrinking = true,
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};
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static bool constraints_initialized __ro_after_init;
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/*
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* Synchronizes accesses to the per-CPU constraints; the locking rules are:
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*
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* 1. Atomic updates to bp_cpuinfo::tsk_pinned only require a held read-lock
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* (due to bp_slots_histogram::count being atomic, no update are lost).
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*
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* 2. Holding a write-lock is required for computations that require a
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* stable snapshot of all bp_cpuinfo::tsk_pinned.
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*
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* 3. In all other cases, non-atomic accesses require the appropriately held
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* lock (read-lock for read-only accesses; write-lock for reads/writes).
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*/
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DEFINE_STATIC_PERCPU_RWSEM(bp_cpuinfo_sem);
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/*
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* Return mutex to serialize accesses to per-task lists in task_bps_ht. Since
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* rhltable synchronizes concurrent insertions/deletions, independent tasks may
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* insert/delete concurrently; therefore, a mutex per task is sufficient.
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*
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* Uses task_struct::perf_event_mutex, to avoid extending task_struct with a
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* hw_breakpoint-only mutex, which may be infrequently used. The caveat here is
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* that hw_breakpoint may contend with per-task perf event list management. The
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* assumption is that perf usecases involving hw_breakpoints are very unlikely
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* to result in unnecessary contention.
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*/
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static inline struct mutex *get_task_bps_mutex(struct perf_event *bp)
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{
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struct task_struct *tsk = bp->hw.target;
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return tsk ? &tsk->perf_event_mutex : NULL;
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}
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static struct mutex *bp_constraints_lock(struct perf_event *bp)
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{
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struct mutex *tsk_mtx = get_task_bps_mutex(bp);
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if (tsk_mtx) {
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/*
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* Fully analogous to the perf_try_init_event() nesting
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* argument in the comment near perf_event_ctx_lock_nested();
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* this child->perf_event_mutex cannot ever deadlock against
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* the parent->perf_event_mutex usage from
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* perf_event_task_{en,dis}able().
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*
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* Specifically, inherited events will never occur on
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* ->perf_event_list.
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*/
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mutex_lock_nested(tsk_mtx, SINGLE_DEPTH_NESTING);
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percpu_down_read(&bp_cpuinfo_sem);
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} else {
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percpu_down_write(&bp_cpuinfo_sem);
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}
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return tsk_mtx;
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}
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static void bp_constraints_unlock(struct mutex *tsk_mtx)
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{
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if (tsk_mtx) {
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percpu_up_read(&bp_cpuinfo_sem);
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mutex_unlock(tsk_mtx);
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} else {
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percpu_up_write(&bp_cpuinfo_sem);
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}
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}
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static bool bp_constraints_is_locked(struct perf_event *bp)
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{
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struct mutex *tsk_mtx = get_task_bps_mutex(bp);
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return percpu_is_write_locked(&bp_cpuinfo_sem) ||
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(tsk_mtx ? mutex_is_locked(tsk_mtx) :
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percpu_is_read_locked(&bp_cpuinfo_sem));
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}
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static inline void assert_bp_constraints_lock_held(struct perf_event *bp)
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{
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struct mutex *tsk_mtx = get_task_bps_mutex(bp);
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if (tsk_mtx)
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lockdep_assert_held(tsk_mtx);
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lockdep_assert_held(&bp_cpuinfo_sem);
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}
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#ifdef hw_breakpoint_slots
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/*
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* Number of breakpoint slots is constant, and the same for all types.
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*/
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static_assert(hw_breakpoint_slots(TYPE_INST) == hw_breakpoint_slots(TYPE_DATA));
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static inline int hw_breakpoint_slots_cached(int type) { return hw_breakpoint_slots(type); }
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static inline int init_breakpoint_slots(void) { return 0; }
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#else
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/*
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* Dynamic number of breakpoint slots.
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*/
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static int __nr_bp_slots[TYPE_MAX] __ro_after_init;
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static inline int hw_breakpoint_slots_cached(int type)
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{
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return __nr_bp_slots[type];
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}
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static __init bool
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bp_slots_histogram_alloc(struct bp_slots_histogram *hist, enum bp_type_idx type)
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{
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hist->count = kcalloc(hw_breakpoint_slots_cached(type), sizeof(*hist->count), GFP_KERNEL);
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return hist->count;
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}
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static __init void bp_slots_histogram_free(struct bp_slots_histogram *hist)
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{
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kfree(hist->count);
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}
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static __init int init_breakpoint_slots(void)
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{
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int i, cpu, err_cpu;
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for (i = 0; i < TYPE_MAX; i++)
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__nr_bp_slots[i] = hw_breakpoint_slots(i);
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for_each_possible_cpu(cpu) {
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for (i = 0; i < TYPE_MAX; i++) {
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struct bp_cpuinfo *info = get_bp_info(cpu, i);
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if (!bp_slots_histogram_alloc(&info->tsk_pinned, i))
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goto err;
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}
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}
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for (i = 0; i < TYPE_MAX; i++) {
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if (!bp_slots_histogram_alloc(&cpu_pinned[i], i))
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goto err;
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if (!bp_slots_histogram_alloc(&tsk_pinned_all[i], i))
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goto err;
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}
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return 0;
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err:
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for_each_possible_cpu(err_cpu) {
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for (i = 0; i < TYPE_MAX; i++)
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bp_slots_histogram_free(&get_bp_info(err_cpu, i)->tsk_pinned);
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if (err_cpu == cpu)
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break;
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}
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for (i = 0; i < TYPE_MAX; i++) {
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bp_slots_histogram_free(&cpu_pinned[i]);
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bp_slots_histogram_free(&tsk_pinned_all[i]);
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}
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return -ENOMEM;
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}
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#endif
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static inline void
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bp_slots_histogram_add(struct bp_slots_histogram *hist, int old, int val)
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{
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const int old_idx = old - 1;
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const int new_idx = old_idx + val;
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if (old_idx >= 0)
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WARN_ON(atomic_dec_return_relaxed(&hist->count[old_idx]) < 0);
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if (new_idx >= 0)
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WARN_ON(atomic_inc_return_relaxed(&hist->count[new_idx]) < 0);
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}
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static int
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bp_slots_histogram_max(struct bp_slots_histogram *hist, enum bp_type_idx type)
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{
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for (int i = hw_breakpoint_slots_cached(type) - 1; i >= 0; i--) {
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const int count = atomic_read(&hist->count[i]);
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/* Catch unexpected writers; we want a stable snapshot. */
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ASSERT_EXCLUSIVE_WRITER(hist->count[i]);
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if (count > 0)
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return i + 1;
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WARN(count < 0, "inconsistent breakpoint slots histogram");
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}
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return 0;
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}
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static int
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bp_slots_histogram_max_merge(struct bp_slots_histogram *hist1, struct bp_slots_histogram *hist2,
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enum bp_type_idx type)
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{
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for (int i = hw_breakpoint_slots_cached(type) - 1; i >= 0; i--) {
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const int count1 = atomic_read(&hist1->count[i]);
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const int count2 = atomic_read(&hist2->count[i]);
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/* Catch unexpected writers; we want a stable snapshot. */
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ASSERT_EXCLUSIVE_WRITER(hist1->count[i]);
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ASSERT_EXCLUSIVE_WRITER(hist2->count[i]);
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if (count1 + count2 > 0)
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return i + 1;
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WARN(count1 < 0, "inconsistent breakpoint slots histogram");
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WARN(count2 < 0, "inconsistent breakpoint slots histogram");
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}
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return 0;
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}
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#ifndef hw_breakpoint_weight
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static inline int hw_breakpoint_weight(struct perf_event *bp)
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{
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return 1;
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}
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#endif
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static inline enum bp_type_idx find_slot_idx(u64 bp_type)
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{
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if (bp_type & HW_BREAKPOINT_RW)
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return TYPE_DATA;
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return TYPE_INST;
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}
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/*
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* Return the maximum number of pinned breakpoints a task has in this CPU.
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*/
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static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
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{
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struct bp_slots_histogram *tsk_pinned = &get_bp_info(cpu, type)->tsk_pinned;
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/*
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* At this point we want to have acquired the bp_cpuinfo_sem as a
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* writer to ensure that there are no concurrent writers in
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* toggle_bp_task_slot() to tsk_pinned, and we get a stable snapshot.
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*/
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lockdep_assert_held_write(&bp_cpuinfo_sem);
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return bp_slots_histogram_max_merge(tsk_pinned, &tsk_pinned_all[type], type);
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}
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/*
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* Count the number of breakpoints of the same type and same task.
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* The given event must be not on the list.
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*
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* If @cpu is -1, but the result of task_bp_pinned() is not CPU-independent,
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* returns a negative value.
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*/
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static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type)
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{
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struct rhlist_head *head, *pos;
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struct perf_event *iter;
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int count = 0;
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/*
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* We need a stable snapshot of the per-task breakpoint list.
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*/
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assert_bp_constraints_lock_held(bp);
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rcu_read_lock();
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head = rhltable_lookup(&task_bps_ht, &bp->hw.target, task_bps_ht_params);
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if (!head)
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goto out;
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rhl_for_each_entry_rcu(iter, pos, head, hw.bp_list) {
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if (find_slot_idx(iter->attr.bp_type) != type)
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continue;
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if (iter->cpu >= 0) {
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if (cpu == -1) {
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count = -1;
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goto out;
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} else if (cpu != iter->cpu)
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continue;
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}
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count += hw_breakpoint_weight(iter);
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}
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out:
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rcu_read_unlock();
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return count;
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}
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static const struct cpumask *cpumask_of_bp(struct perf_event *bp)
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{
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if (bp->cpu >= 0)
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return cpumask_of(bp->cpu);
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return cpu_possible_mask;
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}
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/*
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* Returns the max pinned breakpoint slots in a given
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* CPU (cpu > -1) or across all of them (cpu = -1).
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*/
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static int
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max_bp_pinned_slots(struct perf_event *bp, enum bp_type_idx type)
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{
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const struct cpumask *cpumask = cpumask_of_bp(bp);
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int pinned_slots = 0;
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int cpu;
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if (bp->hw.target && bp->cpu < 0) {
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int max_pinned = task_bp_pinned(-1, bp, type);
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if (max_pinned >= 0) {
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/*
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* Fast path: task_bp_pinned() is CPU-independent and
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* returns the same value for any CPU.
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*/
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max_pinned += bp_slots_histogram_max(&cpu_pinned[type], type);
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return max_pinned;
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}
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}
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for_each_cpu(cpu, cpumask) {
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struct bp_cpuinfo *info = get_bp_info(cpu, type);
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int nr;
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nr = info->cpu_pinned;
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if (!bp->hw.target)
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nr += max_task_bp_pinned(cpu, type);
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else
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nr += task_bp_pinned(cpu, bp, type);
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pinned_slots = max(nr, pinned_slots);
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}
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return pinned_slots;
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}
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/*
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* Add/remove the given breakpoint in our constraint table
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*/
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static int
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toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type, int weight)
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{
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int cpu, next_tsk_pinned;
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if (!enable)
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weight = -weight;
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if (!bp->hw.target) {
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/*
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* Update the pinned CPU slots, in per-CPU bp_cpuinfo and in the
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* global histogram.
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*/
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struct bp_cpuinfo *info = get_bp_info(bp->cpu, type);
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lockdep_assert_held_write(&bp_cpuinfo_sem);
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bp_slots_histogram_add(&cpu_pinned[type], info->cpu_pinned, weight);
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info->cpu_pinned += weight;
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return 0;
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}
|
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|
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/*
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* If bp->hw.target, tsk_pinned is only modified, but not used
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* otherwise. We can permit concurrent updates as long as there are no
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* other uses: having acquired bp_cpuinfo_sem as a reader allows
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* concurrent updates here. Uses of tsk_pinned will require acquiring
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* bp_cpuinfo_sem as a writer to stabilize tsk_pinned's value.
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*/
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lockdep_assert_held_read(&bp_cpuinfo_sem);
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|
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/*
|
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* Update the pinned task slots, in per-CPU bp_cpuinfo and in the global
|
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* histogram. We need to take care of 4 cases:
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*
|
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* 1. This breakpoint targets all CPUs (cpu < 0), and there may only
|
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* exist other task breakpoints targeting all CPUs. In this case we
|
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* can simply update the global slots histogram.
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*
|
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* 2. This breakpoint targets a specific CPU (cpu >= 0), but there may
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* only exist other task breakpoints targeting all CPUs.
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*
|
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* a. On enable: remove the existing breakpoints from the global
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* slots histogram and use the per-CPU histogram.
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*
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* b. On disable: re-insert the existing breakpoints into the global
|
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* slots histogram and remove from per-CPU histogram.
|
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*
|
|
* 3. Some other existing task breakpoints target specific CPUs. Only
|
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* update the per-CPU slots histogram.
|
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*/
|
|
|
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if (!enable) {
|
|
/*
|
|
* Remove before updating histograms so we can determine if this
|
|
* was the last task breakpoint for a specific CPU.
|
|
*/
|
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int ret = rhltable_remove(&task_bps_ht, &bp->hw.bp_list, task_bps_ht_params);
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|
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if (ret)
|
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return ret;
|
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}
|
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/*
|
|
* Note: If !enable, next_tsk_pinned will not count the to-be-removed breakpoint.
|
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*/
|
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next_tsk_pinned = task_bp_pinned(-1, bp, type);
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|
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if (next_tsk_pinned >= 0) {
|
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if (bp->cpu < 0) { /* Case 1: fast path */
|
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if (!enable)
|
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next_tsk_pinned += hw_breakpoint_weight(bp);
|
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bp_slots_histogram_add(&tsk_pinned_all[type], next_tsk_pinned, weight);
|
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} else if (enable) { /* Case 2.a: slow path */
|
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/* Add existing to per-CPU histograms. */
|
|
for_each_possible_cpu(cpu) {
|
|
bp_slots_histogram_add(&get_bp_info(cpu, type)->tsk_pinned,
|
|
0, next_tsk_pinned);
|
|
}
|
|
/* Add this first CPU-pinned task breakpoint. */
|
|
bp_slots_histogram_add(&get_bp_info(bp->cpu, type)->tsk_pinned,
|
|
next_tsk_pinned, weight);
|
|
/* Rebalance global task pinned histogram. */
|
|
bp_slots_histogram_add(&tsk_pinned_all[type], next_tsk_pinned,
|
|
-next_tsk_pinned);
|
|
} else { /* Case 2.b: slow path */
|
|
/* Remove this last CPU-pinned task breakpoint. */
|
|
bp_slots_histogram_add(&get_bp_info(bp->cpu, type)->tsk_pinned,
|
|
next_tsk_pinned + hw_breakpoint_weight(bp), weight);
|
|
/* Remove all from per-CPU histograms. */
|
|
for_each_possible_cpu(cpu) {
|
|
bp_slots_histogram_add(&get_bp_info(cpu, type)->tsk_pinned,
|
|
next_tsk_pinned, -next_tsk_pinned);
|
|
}
|
|
/* Rebalance global task pinned histogram. */
|
|
bp_slots_histogram_add(&tsk_pinned_all[type], 0, next_tsk_pinned);
|
|
}
|
|
} else { /* Case 3: slow path */
|
|
const struct cpumask *cpumask = cpumask_of_bp(bp);
|
|
|
|
for_each_cpu(cpu, cpumask) {
|
|
next_tsk_pinned = task_bp_pinned(cpu, bp, type);
|
|
if (!enable)
|
|
next_tsk_pinned += hw_breakpoint_weight(bp);
|
|
bp_slots_histogram_add(&get_bp_info(cpu, type)->tsk_pinned,
|
|
next_tsk_pinned, weight);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Readers want a stable snapshot of the per-task breakpoint list.
|
|
*/
|
|
assert_bp_constraints_lock_held(bp);
|
|
|
|
if (enable)
|
|
return rhltable_insert(&task_bps_ht, &bp->hw.bp_list, task_bps_ht_params);
|
|
|
|
return 0;
|
|
}
|
|
|
|
__weak int arch_reserve_bp_slot(struct perf_event *bp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
__weak void arch_release_bp_slot(struct perf_event *bp)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Function to perform processor-specific cleanup during unregistration
|
|
*/
|
|
__weak void arch_unregister_hw_breakpoint(struct perf_event *bp)
|
|
{
|
|
/*
|
|
* A weak stub function here for those archs that don't define
|
|
* it inside arch/.../kernel/hw_breakpoint.c
|
|
*/
|
|
}
|
|
|
|
/*
|
|
* Constraints to check before allowing this new breakpoint counter.
|
|
*
|
|
* Note: Flexible breakpoints are currently unimplemented, but outlined in the
|
|
* below algorithm for completeness. The implementation treats flexible as
|
|
* pinned due to no guarantee that we currently always schedule flexible events
|
|
* before a pinned event in a same CPU.
|
|
*
|
|
* == Non-pinned counter == (Considered as pinned for now)
|
|
*
|
|
* - If attached to a single cpu, check:
|
|
*
|
|
* (per_cpu(info->flexible, cpu) || (per_cpu(info->cpu_pinned, cpu)
|
|
* + max(per_cpu(info->tsk_pinned, cpu)))) < HBP_NUM
|
|
*
|
|
* -> If there are already non-pinned counters in this cpu, it means
|
|
* there is already a free slot for them.
|
|
* Otherwise, we check that the maximum number of per task
|
|
* breakpoints (for this cpu) plus the number of per cpu breakpoint
|
|
* (for this cpu) doesn't cover every registers.
|
|
*
|
|
* - If attached to every cpus, check:
|
|
*
|
|
* (per_cpu(info->flexible, *) || (max(per_cpu(info->cpu_pinned, *))
|
|
* + max(per_cpu(info->tsk_pinned, *)))) < HBP_NUM
|
|
*
|
|
* -> This is roughly the same, except we check the number of per cpu
|
|
* bp for every cpu and we keep the max one. Same for the per tasks
|
|
* breakpoints.
|
|
*
|
|
*
|
|
* == Pinned counter ==
|
|
*
|
|
* - If attached to a single cpu, check:
|
|
*
|
|
* ((per_cpu(info->flexible, cpu) > 1) + per_cpu(info->cpu_pinned, cpu)
|
|
* + max(per_cpu(info->tsk_pinned, cpu))) < HBP_NUM
|
|
*
|
|
* -> Same checks as before. But now the info->flexible, if any, must keep
|
|
* one register at least (or they will never be fed).
|
|
*
|
|
* - If attached to every cpus, check:
|
|
*
|
|
* ((per_cpu(info->flexible, *) > 1) + max(per_cpu(info->cpu_pinned, *))
|
|
* + max(per_cpu(info->tsk_pinned, *))) < HBP_NUM
|
|
*/
|
|
static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type)
|
|
{
|
|
enum bp_type_idx type;
|
|
int max_pinned_slots;
|
|
int weight;
|
|
int ret;
|
|
|
|
/* We couldn't initialize breakpoint constraints on boot */
|
|
if (!constraints_initialized)
|
|
return -ENOMEM;
|
|
|
|
/* Basic checks */
|
|
if (bp_type == HW_BREAKPOINT_EMPTY ||
|
|
bp_type == HW_BREAKPOINT_INVALID)
|
|
return -EINVAL;
|
|
|
|
type = find_slot_idx(bp_type);
|
|
weight = hw_breakpoint_weight(bp);
|
|
|
|
/* Check if this new breakpoint can be satisfied across all CPUs. */
|
|
max_pinned_slots = max_bp_pinned_slots(bp, type) + weight;
|
|
if (max_pinned_slots > hw_breakpoint_slots_cached(type))
|
|
return -ENOSPC;
|
|
|
|
ret = arch_reserve_bp_slot(bp);
|
|
if (ret)
|
|
return ret;
|
|
|
|
return toggle_bp_slot(bp, true, type, weight);
|
|
}
|
|
|
|
int reserve_bp_slot(struct perf_event *bp)
|
|
{
|
|
struct mutex *mtx = bp_constraints_lock(bp);
|
|
int ret = __reserve_bp_slot(bp, bp->attr.bp_type);
|
|
|
|
bp_constraints_unlock(mtx);
|
|
return ret;
|
|
}
|
|
|
|
static void __release_bp_slot(struct perf_event *bp, u64 bp_type)
|
|
{
|
|
enum bp_type_idx type;
|
|
int weight;
|
|
|
|
arch_release_bp_slot(bp);
|
|
|
|
type = find_slot_idx(bp_type);
|
|
weight = hw_breakpoint_weight(bp);
|
|
WARN_ON(toggle_bp_slot(bp, false, type, weight));
|
|
}
|
|
|
|
void release_bp_slot(struct perf_event *bp)
|
|
{
|
|
struct mutex *mtx = bp_constraints_lock(bp);
|
|
|
|
arch_unregister_hw_breakpoint(bp);
|
|
__release_bp_slot(bp, bp->attr.bp_type);
|
|
bp_constraints_unlock(mtx);
|
|
}
|
|
|
|
static int __modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
|
|
{
|
|
int err;
|
|
|
|
__release_bp_slot(bp, old_type);
|
|
|
|
err = __reserve_bp_slot(bp, new_type);
|
|
if (err) {
|
|
/*
|
|
* Reserve the old_type slot back in case
|
|
* there's no space for the new type.
|
|
*
|
|
* This must succeed, because we just released
|
|
* the old_type slot in the __release_bp_slot
|
|
* call above. If not, something is broken.
|
|
*/
|
|
WARN_ON(__reserve_bp_slot(bp, old_type));
|
|
}
|
|
|
|
return err;
|
|
}
|
|
|
|
static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
|
|
{
|
|
struct mutex *mtx = bp_constraints_lock(bp);
|
|
int ret = __modify_bp_slot(bp, old_type, new_type);
|
|
|
|
bp_constraints_unlock(mtx);
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Allow the kernel debugger to reserve breakpoint slots without
|
|
* taking a lock using the dbg_* variant of for the reserve and
|
|
* release breakpoint slots.
|
|
*/
|
|
int dbg_reserve_bp_slot(struct perf_event *bp)
|
|
{
|
|
int ret;
|
|
|
|
if (bp_constraints_is_locked(bp))
|
|
return -1;
|
|
|
|
/* Locks aren't held; disable lockdep assert checking. */
|
|
lockdep_off();
|
|
ret = __reserve_bp_slot(bp, bp->attr.bp_type);
|
|
lockdep_on();
|
|
|
|
return ret;
|
|
}
|
|
|
|
int dbg_release_bp_slot(struct perf_event *bp)
|
|
{
|
|
if (bp_constraints_is_locked(bp))
|
|
return -1;
|
|
|
|
/* Locks aren't held; disable lockdep assert checking. */
|
|
lockdep_off();
|
|
__release_bp_slot(bp, bp->attr.bp_type);
|
|
lockdep_on();
|
|
|
|
return 0;
|
|
}
|
|
|
|
static int hw_breakpoint_parse(struct perf_event *bp,
|
|
const struct perf_event_attr *attr,
|
|
struct arch_hw_breakpoint *hw)
|
|
{
|
|
int err;
|
|
|
|
err = hw_breakpoint_arch_parse(bp, attr, hw);
|
|
if (err)
|
|
return err;
|
|
|
|
if (arch_check_bp_in_kernelspace(hw)) {
|
|
if (attr->exclude_kernel)
|
|
return -EINVAL;
|
|
/*
|
|
* Don't let unprivileged users set a breakpoint in the trap
|
|
* path to avoid trap recursion attacks.
|
|
*/
|
|
if (!capable(CAP_SYS_ADMIN))
|
|
return -EPERM;
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
int register_perf_hw_breakpoint(struct perf_event *bp)
|
|
{
|
|
struct arch_hw_breakpoint hw = { };
|
|
int err;
|
|
|
|
err = reserve_bp_slot(bp);
|
|
if (err)
|
|
return err;
|
|
|
|
err = hw_breakpoint_parse(bp, &bp->attr, &hw);
|
|
if (err) {
|
|
release_bp_slot(bp);
|
|
return err;
|
|
}
|
|
|
|
bp->hw.info = hw;
|
|
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* register_user_hw_breakpoint - register a hardware breakpoint for user space
|
|
* @attr: breakpoint attributes
|
|
* @triggered: callback to trigger when we hit the breakpoint
|
|
* @context: context data could be used in the triggered callback
|
|
* @tsk: pointer to 'task_struct' of the process to which the address belongs
|
|
*/
|
|
struct perf_event *
|
|
register_user_hw_breakpoint(struct perf_event_attr *attr,
|
|
perf_overflow_handler_t triggered,
|
|
void *context,
|
|
struct task_struct *tsk)
|
|
{
|
|
return perf_event_create_kernel_counter(attr, -1, tsk, triggered,
|
|
context);
|
|
}
|
|
EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
|
|
|
|
static void hw_breakpoint_copy_attr(struct perf_event_attr *to,
|
|
struct perf_event_attr *from)
|
|
{
|
|
to->bp_addr = from->bp_addr;
|
|
to->bp_type = from->bp_type;
|
|
to->bp_len = from->bp_len;
|
|
to->disabled = from->disabled;
|
|
}
|
|
|
|
int
|
|
modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
|
|
bool check)
|
|
{
|
|
struct arch_hw_breakpoint hw = { };
|
|
int err;
|
|
|
|
err = hw_breakpoint_parse(bp, attr, &hw);
|
|
if (err)
|
|
return err;
|
|
|
|
if (check) {
|
|
struct perf_event_attr old_attr;
|
|
|
|
old_attr = bp->attr;
|
|
hw_breakpoint_copy_attr(&old_attr, attr);
|
|
if (memcmp(&old_attr, attr, sizeof(*attr)))
|
|
return -EINVAL;
|
|
}
|
|
|
|
if (bp->attr.bp_type != attr->bp_type) {
|
|
err = modify_bp_slot(bp, bp->attr.bp_type, attr->bp_type);
|
|
if (err)
|
|
return err;
|
|
}
|
|
|
|
hw_breakpoint_copy_attr(&bp->attr, attr);
|
|
bp->hw.info = hw;
|
|
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* modify_user_hw_breakpoint - modify a user-space hardware breakpoint
|
|
* @bp: the breakpoint structure to modify
|
|
* @attr: new breakpoint attributes
|
|
*/
|
|
int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
|
|
{
|
|
int err;
|
|
|
|
/*
|
|
* modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
|
|
* will not be possible to raise IPIs that invoke __perf_event_disable.
|
|
* So call the function directly after making sure we are targeting the
|
|
* current task.
|
|
*/
|
|
if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
|
|
perf_event_disable_local(bp);
|
|
else
|
|
perf_event_disable(bp);
|
|
|
|
err = modify_user_hw_breakpoint_check(bp, attr, false);
|
|
|
|
if (!bp->attr.disabled)
|
|
perf_event_enable(bp);
|
|
|
|
return err;
|
|
}
|
|
EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
|
|
|
|
/**
|
|
* unregister_hw_breakpoint - unregister a user-space hardware breakpoint
|
|
* @bp: the breakpoint structure to unregister
|
|
*/
|
|
void unregister_hw_breakpoint(struct perf_event *bp)
|
|
{
|
|
if (!bp)
|
|
return;
|
|
perf_event_release_kernel(bp);
|
|
}
|
|
EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
|
|
|
|
/**
|
|
* register_wide_hw_breakpoint - register a wide breakpoint in the kernel
|
|
* @attr: breakpoint attributes
|
|
* @triggered: callback to trigger when we hit the breakpoint
|
|
* @context: context data could be used in the triggered callback
|
|
*
|
|
* @return a set of per_cpu pointers to perf events
|
|
*/
|
|
struct perf_event * __percpu *
|
|
register_wide_hw_breakpoint(struct perf_event_attr *attr,
|
|
perf_overflow_handler_t triggered,
|
|
void *context)
|
|
{
|
|
struct perf_event * __percpu *cpu_events, *bp;
|
|
long err = 0;
|
|
int cpu;
|
|
|
|
cpu_events = alloc_percpu(typeof(*cpu_events));
|
|
if (!cpu_events)
|
|
return (void __percpu __force *)ERR_PTR(-ENOMEM);
|
|
|
|
cpus_read_lock();
|
|
for_each_online_cpu(cpu) {
|
|
bp = perf_event_create_kernel_counter(attr, cpu, NULL,
|
|
triggered, context);
|
|
if (IS_ERR(bp)) {
|
|
err = PTR_ERR(bp);
|
|
break;
|
|
}
|
|
|
|
per_cpu(*cpu_events, cpu) = bp;
|
|
}
|
|
cpus_read_unlock();
|
|
|
|
if (likely(!err))
|
|
return cpu_events;
|
|
|
|
unregister_wide_hw_breakpoint(cpu_events);
|
|
return (void __percpu __force *)ERR_PTR(err);
|
|
}
|
|
EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
|
|
|
|
/**
|
|
* unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
|
|
* @cpu_events: the per cpu set of events to unregister
|
|
*/
|
|
void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
|
|
{
|
|
int cpu;
|
|
|
|
for_each_possible_cpu(cpu)
|
|
unregister_hw_breakpoint(per_cpu(*cpu_events, cpu));
|
|
|
|
free_percpu(cpu_events);
|
|
}
|
|
EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
|
|
|
|
/**
|
|
* hw_breakpoint_is_used - check if breakpoints are currently used
|
|
*
|
|
* Returns: true if breakpoints are used, false otherwise.
|
|
*/
|
|
bool hw_breakpoint_is_used(void)
|
|
{
|
|
int cpu;
|
|
|
|
if (!constraints_initialized)
|
|
return false;
|
|
|
|
for_each_possible_cpu(cpu) {
|
|
for (int type = 0; type < TYPE_MAX; ++type) {
|
|
struct bp_cpuinfo *info = get_bp_info(cpu, type);
|
|
|
|
if (info->cpu_pinned)
|
|
return true;
|
|
|
|
for (int slot = 0; slot < hw_breakpoint_slots_cached(type); ++slot) {
|
|
if (atomic_read(&info->tsk_pinned.count[slot]))
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
|
|
for (int type = 0; type < TYPE_MAX; ++type) {
|
|
for (int slot = 0; slot < hw_breakpoint_slots_cached(type); ++slot) {
|
|
/*
|
|
* Warn, because if there are CPU pinned counters,
|
|
* should never get here; bp_cpuinfo::cpu_pinned should
|
|
* be consistent with the global cpu_pinned histogram.
|
|
*/
|
|
if (WARN_ON(atomic_read(&cpu_pinned[type].count[slot])))
|
|
return true;
|
|
|
|
if (atomic_read(&tsk_pinned_all[type].count[slot]))
|
|
return true;
|
|
}
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
static struct notifier_block hw_breakpoint_exceptions_nb = {
|
|
.notifier_call = hw_breakpoint_exceptions_notify,
|
|
/* we need to be notified first */
|
|
.priority = 0x7fffffff
|
|
};
|
|
|
|
static void bp_perf_event_destroy(struct perf_event *event)
|
|
{
|
|
release_bp_slot(event);
|
|
}
|
|
|
|
static int hw_breakpoint_event_init(struct perf_event *bp)
|
|
{
|
|
int err;
|
|
|
|
if (bp->attr.type != PERF_TYPE_BREAKPOINT)
|
|
return -ENOENT;
|
|
|
|
/*
|
|
* no branch sampling for breakpoint events
|
|
*/
|
|
if (has_branch_stack(bp))
|
|
return -EOPNOTSUPP;
|
|
|
|
err = register_perf_hw_breakpoint(bp);
|
|
if (err)
|
|
return err;
|
|
|
|
bp->destroy = bp_perf_event_destroy;
|
|
|
|
return 0;
|
|
}
|
|
|
|
static int hw_breakpoint_add(struct perf_event *bp, int flags)
|
|
{
|
|
if (!(flags & PERF_EF_START))
|
|
bp->hw.state = PERF_HES_STOPPED;
|
|
|
|
if (is_sampling_event(bp)) {
|
|
bp->hw.last_period = bp->hw.sample_period;
|
|
perf_swevent_set_period(bp);
|
|
}
|
|
|
|
return arch_install_hw_breakpoint(bp);
|
|
}
|
|
|
|
static void hw_breakpoint_del(struct perf_event *bp, int flags)
|
|
{
|
|
arch_uninstall_hw_breakpoint(bp);
|
|
}
|
|
|
|
static void hw_breakpoint_start(struct perf_event *bp, int flags)
|
|
{
|
|
bp->hw.state = 0;
|
|
}
|
|
|
|
static void hw_breakpoint_stop(struct perf_event *bp, int flags)
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{
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bp->hw.state = PERF_HES_STOPPED;
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}
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static struct pmu perf_breakpoint = {
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.task_ctx_nr = perf_sw_context, /* could eventually get its own */
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.event_init = hw_breakpoint_event_init,
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.add = hw_breakpoint_add,
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.del = hw_breakpoint_del,
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.start = hw_breakpoint_start,
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.stop = hw_breakpoint_stop,
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.read = hw_breakpoint_pmu_read,
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};
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int __init init_hw_breakpoint(void)
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|
{
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int ret;
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|
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ret = rhltable_init(&task_bps_ht, &task_bps_ht_params);
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if (ret)
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return ret;
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|
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ret = init_breakpoint_slots();
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|
if (ret)
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return ret;
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|
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constraints_initialized = true;
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|
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perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);
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|
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return register_die_notifier(&hw_breakpoint_exceptions_nb);
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}
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