linux-stable/kernel/hw_breakpoint.c
Frederic Weisbecker 44234adcdc hw-breakpoints: Modify breakpoints without unregistering them
Currently, when ptrace needs to modify a breakpoint, like disabling
it, changing its address, type or len, it calls
modify_user_hw_breakpoint(). This latter will perform the heavy and
racy task of unregistering the old breakpoint and registering a new
one.

This is racy as someone else might steal the reserved breakpoint
slot under us, which is undesired as the breakpoint is only
supposed to be modified, sometimes in the middle of a debugging
workflow. We don't want our slot to be stolen in the middle.

So instead of unregistering/registering the breakpoint, just
disable it while we modify its breakpoint fields and re-enable it
after if necessary.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prasad <prasad@linux.vnet.ibm.com>
LKML-Reference: <1260347148-5519-1-git-send-regression-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-12-09 09:48:20 +01:00

453 lines
11 KiB
C

/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright (C) 2007 Alan Stern
* Copyright (C) IBM Corporation, 2009
* Copyright (C) 2009, Frederic Weisbecker <fweisbec@gmail.com>
*
* Thanks to Ingo Molnar for his many suggestions.
*
* Authors: Alan Stern <stern@rowland.harvard.edu>
* K.Prasad <prasad@linux.vnet.ibm.com>
* Frederic Weisbecker <fweisbec@gmail.com>
*/
/*
* HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
* using the CPU's debug registers.
* This file contains the arch-independent routines.
*/
#include <linux/irqflags.h>
#include <linux/kallsyms.h>
#include <linux/notifier.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/hw_breakpoint.h>
/*
* Constraints data
*/
/* Number of pinned cpu breakpoints in a cpu */
static DEFINE_PER_CPU(unsigned int, nr_cpu_bp_pinned);
/* Number of pinned task breakpoints in a cpu */
static DEFINE_PER_CPU(unsigned int, nr_task_bp_pinned[HBP_NUM]);
/* Number of non-pinned cpu/task breakpoints in a cpu */
static DEFINE_PER_CPU(unsigned int, nr_bp_flexible);
/* Gather the number of total pinned and un-pinned bp in a cpuset */
struct bp_busy_slots {
unsigned int pinned;
unsigned int flexible;
};
/* Serialize accesses to the above constraints */
static DEFINE_MUTEX(nr_bp_mutex);
/*
* Report the maximum number of pinned breakpoints a task
* have in this cpu
*/
static unsigned int max_task_bp_pinned(int cpu)
{
int i;
unsigned int *tsk_pinned = per_cpu(nr_task_bp_pinned, cpu);
for (i = HBP_NUM -1; i >= 0; i--) {
if (tsk_pinned[i] > 0)
return i + 1;
}
return 0;
}
static int task_bp_pinned(struct task_struct *tsk)
{
struct perf_event_context *ctx = tsk->perf_event_ctxp;
struct list_head *list;
struct perf_event *bp;
unsigned long flags;
int count = 0;
if (WARN_ONCE(!ctx, "No perf context for this task"))
return 0;
list = &ctx->event_list;
spin_lock_irqsave(&ctx->lock, flags);
/*
* The current breakpoint counter is not included in the list
* at the open() callback time
*/
list_for_each_entry(bp, list, event_entry) {
if (bp->attr.type == PERF_TYPE_BREAKPOINT)
count++;
}
spin_unlock_irqrestore(&ctx->lock, flags);
return count;
}
/*
* Report the number of pinned/un-pinned breakpoints we have in
* a given cpu (cpu > -1) or in all of them (cpu = -1).
*/
static void
fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp)
{
int cpu = bp->cpu;
struct task_struct *tsk = bp->ctx->task;
if (cpu >= 0) {
slots->pinned = per_cpu(nr_cpu_bp_pinned, cpu);
if (!tsk)
slots->pinned += max_task_bp_pinned(cpu);
else
slots->pinned += task_bp_pinned(tsk);
slots->flexible = per_cpu(nr_bp_flexible, cpu);
return;
}
for_each_online_cpu(cpu) {
unsigned int nr;
nr = per_cpu(nr_cpu_bp_pinned, cpu);
if (!tsk)
nr += max_task_bp_pinned(cpu);
else
nr += task_bp_pinned(tsk);
if (nr > slots->pinned)
slots->pinned = nr;
nr = per_cpu(nr_bp_flexible, cpu);
if (nr > slots->flexible)
slots->flexible = nr;
}
}
/*
* Add a pinned breakpoint for the given task in our constraint table
*/
static void toggle_bp_task_slot(struct task_struct *tsk, int cpu, bool enable)
{
unsigned int *tsk_pinned;
int count = 0;
count = task_bp_pinned(tsk);
tsk_pinned = per_cpu(nr_task_bp_pinned, cpu);
if (enable) {
tsk_pinned[count]++;
if (count > 0)
tsk_pinned[count-1]--;
} else {
tsk_pinned[count]--;
if (count > 0)
tsk_pinned[count-1]++;
}
}
/*
* Add/remove the given breakpoint in our constraint table
*/
static void toggle_bp_slot(struct perf_event *bp, bool enable)
{
int cpu = bp->cpu;
struct task_struct *tsk = bp->ctx->task;
/* Pinned counter task profiling */
if (tsk) {
if (cpu >= 0) {
toggle_bp_task_slot(tsk, cpu, enable);
return;
}
for_each_online_cpu(cpu)
toggle_bp_task_slot(tsk, cpu, enable);
return;
}
/* Pinned counter cpu profiling */
if (enable)
per_cpu(nr_cpu_bp_pinned, bp->cpu)++;
else
per_cpu(nr_cpu_bp_pinned, bp->cpu)--;
}
/*
* Contraints to check before allowing this new breakpoint counter:
*
* == Non-pinned counter == (Considered as pinned for now)
*
* - If attached to a single cpu, check:
*
* (per_cpu(nr_bp_flexible, cpu) || (per_cpu(nr_cpu_bp_pinned, cpu)
* + max(per_cpu(nr_task_bp_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(nr_bp_flexible, *) || (max(per_cpu(nr_cpu_bp_pinned, *))
* + max(per_cpu(nr_task_bp_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(nr_bp_flexible, cpu) > 1) + per_cpu(nr_cpu_bp_pinned, cpu)
* + max(per_cpu(nr_task_bp_pinned, cpu))) < HBP_NUM
*
* -> Same checks as before. But now the nr_bp_flexible, if any, must keep
* one register at least (or they will never be fed).
*
* - If attached to every cpus, check:
*
* ((per_cpu(nr_bp_flexible, *) > 1) + max(per_cpu(nr_cpu_bp_pinned, *))
* + max(per_cpu(nr_task_bp_pinned, *))) < HBP_NUM
*/
int reserve_bp_slot(struct perf_event *bp)
{
struct bp_busy_slots slots = {0};
int ret = 0;
mutex_lock(&nr_bp_mutex);
fetch_bp_busy_slots(&slots, bp);
/* Flexible counters need to keep at least one slot */
if (slots.pinned + (!!slots.flexible) == HBP_NUM) {
ret = -ENOSPC;
goto end;
}
toggle_bp_slot(bp, true);
end:
mutex_unlock(&nr_bp_mutex);
return ret;
}
void release_bp_slot(struct perf_event *bp)
{
mutex_lock(&nr_bp_mutex);
toggle_bp_slot(bp, false);
mutex_unlock(&nr_bp_mutex);
}
int register_perf_hw_breakpoint(struct perf_event *bp)
{
int ret;
ret = reserve_bp_slot(bp);
if (ret)
return ret;
/*
* Ptrace breakpoints can be temporary perf events only
* meant to reserve a slot. In this case, it is created disabled and
* we don't want to check the params right now (as we put a null addr)
* But perf tools create events as disabled and we want to check
* the params for them.
* This is a quick hack that will be removed soon, once we remove
* the tmp breakpoints from ptrace
*/
if (!bp->attr.disabled || !bp->overflow_handler)
ret = arch_validate_hwbkpt_settings(bp, bp->ctx->task);
return ret;
}
/**
* register_user_hw_breakpoint - register a hardware breakpoint for user space
* @attr: breakpoint attributes
* @triggered: callback to trigger when we hit the breakpoint
* @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,
struct task_struct *tsk)
{
return perf_event_create_kernel_counter(attr, -1, tsk->pid, triggered);
}
EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
/**
* modify_user_hw_breakpoint - modify a user-space hardware breakpoint
* @bp: the breakpoint structure to modify
* @attr: new breakpoint attributes
* @triggered: callback to trigger when we hit the breakpoint
* @tsk: pointer to 'task_struct' of the process to which the address belongs
*/
int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
{
u64 old_addr = bp->attr.bp_addr;
int old_type = bp->attr.bp_type;
int old_len = bp->attr.bp_len;
int err = 0;
perf_event_disable(bp);
bp->attr.bp_addr = attr->bp_addr;
bp->attr.bp_type = attr->bp_type;
bp->attr.bp_len = attr->bp_len;
if (attr->disabled)
goto end;
err = arch_validate_hwbkpt_settings(bp, bp->ctx->task);
if (!err)
perf_event_enable(bp);
if (err) {
bp->attr.bp_addr = old_addr;
bp->attr.bp_type = old_type;
bp->attr.bp_len = old_len;
if (!bp->attr.disabled)
perf_event_enable(bp);
return err;
}
end:
bp->attr.disabled = attr->disabled;
return 0;
}
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
*
* @return a set of per_cpu pointers to perf events
*/
struct perf_event **
register_wide_hw_breakpoint(struct perf_event_attr *attr,
perf_overflow_handler_t triggered)
{
struct perf_event **cpu_events, **pevent, *bp;
long err;
int cpu;
cpu_events = alloc_percpu(typeof(*cpu_events));
if (!cpu_events)
return ERR_PTR(-ENOMEM);
for_each_possible_cpu(cpu) {
pevent = per_cpu_ptr(cpu_events, cpu);
bp = perf_event_create_kernel_counter(attr, cpu, -1, triggered);
*pevent = bp;
if (IS_ERR(bp)) {
err = PTR_ERR(bp);
goto fail;
}
}
return cpu_events;
fail:
for_each_possible_cpu(cpu) {
pevent = per_cpu_ptr(cpu_events, cpu);
if (IS_ERR(*pevent))
break;
unregister_hw_breakpoint(*pevent);
}
free_percpu(cpu_events);
/* return the error if any */
return 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 **cpu_events)
{
int cpu;
struct perf_event **pevent;
for_each_possible_cpu(cpu) {
pevent = per_cpu_ptr(cpu_events, cpu);
unregister_hw_breakpoint(*pevent);
}
free_percpu(cpu_events);
}
EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
static struct notifier_block hw_breakpoint_exceptions_nb = {
.notifier_call = hw_breakpoint_exceptions_notify,
/* we need to be notified first */
.priority = 0x7fffffff
};
static int __init init_hw_breakpoint(void)
{
return register_die_notifier(&hw_breakpoint_exceptions_nb);
}
core_initcall(init_hw_breakpoint);
struct pmu perf_ops_bp = {
.enable = arch_install_hw_breakpoint,
.disable = arch_uninstall_hw_breakpoint,
.read = hw_breakpoint_pmu_read,
.unthrottle = hw_breakpoint_pmu_unthrottle
};