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![Frederic Weisbecker](/assets/img/avatar_default.png)
When we fail to allocate the callchain buffers, we roll back the refcount we did and return from get_callchain_buffers(). However we take the refcount and allocate under the callchain lock but the rollback is done outside the lock. As a result, while we roll back, some concurrent callchain user may call get_callchain_buffers(), see the non-zero refcount and give up because the buffers are NULL without itself retrying the allocation. The consequences aren't that bad but that behaviour looks weird enough and it's better to give their chances to the following callchain users where we failed. Reported-by: Jiri Olsa <jolsa@redhat.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Acked-by: Jiri Olsa <jolsa@redhat.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Stephane Eranian <eranian@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1375460996-16329-2-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
209 lines
4.3 KiB
C
209 lines
4.3 KiB
C
/*
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* Performance events callchain code, extracted from core.c:
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*
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* Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
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* Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
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* Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
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* Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
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*
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* For licensing details see kernel-base/COPYING
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*/
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#include <linux/perf_event.h>
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#include <linux/slab.h>
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#include "internal.h"
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struct callchain_cpus_entries {
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struct rcu_head rcu_head;
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struct perf_callchain_entry *cpu_entries[0];
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};
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static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
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static atomic_t nr_callchain_events;
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static DEFINE_MUTEX(callchain_mutex);
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static struct callchain_cpus_entries *callchain_cpus_entries;
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__weak void perf_callchain_kernel(struct perf_callchain_entry *entry,
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struct pt_regs *regs)
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{
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}
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__weak void perf_callchain_user(struct perf_callchain_entry *entry,
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struct pt_regs *regs)
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{
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}
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static void release_callchain_buffers_rcu(struct rcu_head *head)
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{
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struct callchain_cpus_entries *entries;
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int cpu;
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entries = container_of(head, struct callchain_cpus_entries, rcu_head);
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for_each_possible_cpu(cpu)
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kfree(entries->cpu_entries[cpu]);
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kfree(entries);
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}
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static void release_callchain_buffers(void)
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{
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struct callchain_cpus_entries *entries;
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entries = callchain_cpus_entries;
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rcu_assign_pointer(callchain_cpus_entries, NULL);
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call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
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}
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static int alloc_callchain_buffers(void)
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{
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int cpu;
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int size;
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struct callchain_cpus_entries *entries;
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/*
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* We can't use the percpu allocation API for data that can be
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* accessed from NMI. Use a temporary manual per cpu allocation
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* until that gets sorted out.
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*/
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size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);
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entries = kzalloc(size, GFP_KERNEL);
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if (!entries)
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return -ENOMEM;
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size = sizeof(struct perf_callchain_entry) * PERF_NR_CONTEXTS;
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for_each_possible_cpu(cpu) {
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entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
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cpu_to_node(cpu));
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if (!entries->cpu_entries[cpu])
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goto fail;
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}
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rcu_assign_pointer(callchain_cpus_entries, entries);
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return 0;
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fail:
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for_each_possible_cpu(cpu)
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kfree(entries->cpu_entries[cpu]);
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kfree(entries);
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return -ENOMEM;
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}
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int get_callchain_buffers(void)
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{
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int err = 0;
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int count;
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mutex_lock(&callchain_mutex);
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count = atomic_inc_return(&nr_callchain_events);
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if (WARN_ON_ONCE(count < 1)) {
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err = -EINVAL;
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goto exit;
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}
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if (count > 1) {
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/* If the allocation failed, give up */
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if (!callchain_cpus_entries)
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err = -ENOMEM;
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goto exit;
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}
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err = alloc_callchain_buffers();
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exit:
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if (err)
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atomic_dec(&nr_callchain_events);
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mutex_unlock(&callchain_mutex);
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return err;
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}
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void put_callchain_buffers(void)
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{
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if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
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release_callchain_buffers();
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mutex_unlock(&callchain_mutex);
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}
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}
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static struct perf_callchain_entry *get_callchain_entry(int *rctx)
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{
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int cpu;
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struct callchain_cpus_entries *entries;
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*rctx = get_recursion_context(__get_cpu_var(callchain_recursion));
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if (*rctx == -1)
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return NULL;
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entries = rcu_dereference(callchain_cpus_entries);
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if (!entries)
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return NULL;
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cpu = smp_processor_id();
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return &entries->cpu_entries[cpu][*rctx];
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}
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static void
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put_callchain_entry(int rctx)
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{
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put_recursion_context(__get_cpu_var(callchain_recursion), rctx);
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}
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struct perf_callchain_entry *
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perf_callchain(struct perf_event *event, struct pt_regs *regs)
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{
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int rctx;
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struct perf_callchain_entry *entry;
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int kernel = !event->attr.exclude_callchain_kernel;
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int user = !event->attr.exclude_callchain_user;
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if (!kernel && !user)
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return NULL;
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entry = get_callchain_entry(&rctx);
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if (rctx == -1)
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return NULL;
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if (!entry)
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goto exit_put;
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entry->nr = 0;
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if (kernel && !user_mode(regs)) {
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perf_callchain_store(entry, PERF_CONTEXT_KERNEL);
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perf_callchain_kernel(entry, regs);
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}
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if (user) {
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if (!user_mode(regs)) {
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if (current->mm)
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regs = task_pt_regs(current);
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else
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regs = NULL;
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}
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if (regs) {
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/*
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* Disallow cross-task user callchains.
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*/
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if (event->ctx->task && event->ctx->task != current)
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goto exit_put;
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perf_callchain_store(entry, PERF_CONTEXT_USER);
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perf_callchain_user(entry, regs);
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}
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}
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exit_put:
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put_callchain_entry(rctx);
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return entry;
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}
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