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perf: Close install vs. exit race

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Consider the following scenario:

  CPU0					CPU1

  ctx = find_get_ctx();
					perf_event_exit_task_context()
  mutex_lock(&ctx->mutex);
  perf_install_in_context(ctx, ...);
    /* NO-OP */
  mutex_unlock(&ctx->mutex);

  ...

  perf_release()
    WARN_ON_ONCE(event->state != STATE_EXIT);

Since the event doesn't pass through perf_remove_from_context()
because perf_install_in_context() NO-OPs because the ctx is dead, and
perf_event_exit_task_context() will not observe the event because its
not attached yet, the event->state will not be set.

Solve this by revalidating ctx->task after we acquire ctx->mutex and
failing the event creation as a whole.

Tested-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dvyukov@google.com
Cc: eranian@google.com
Cc: oleg@redhat.com
Cc: panand@redhat.com
Cc: sasha.levin@oracle.com
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/20160224174947.626853419@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2016-02-24 18:45:40 +01:00 committed by Ingo Molnar
parent 6dc390ad61
commit 84c4e620d3
1 changed files with 26 additions and 9 deletions
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35
kernel/events/core.c
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@ -2158,13 +2158,15 @@ perf_install_in_context(struct perf_event_context *ctx,
*/
raw_spin_lock_irq(&ctx->lock);
task = ctx->task;
/*
* Worse, we cannot even rely on the ctx actually existing anymore. If
* between find_get_context() and perf_install_in_context() the task
* went through perf_event_exit_task() its dead and we should not be
* adding new events.
* If between ctx = find_get_context() and mutex_lock(&ctx->mutex) the
* ctx gets destroyed, we must not install an event into it.
*
* This is normally tested for after we acquire the mutex, so this is
* a sanity check.
*/
if (task == TASK_TOMBSTONE) {
if (WARN_ON_ONCE(task == TASK_TOMBSTONE)) {
raw_spin_unlock_irq(&ctx->lock);
return;
}
@ -8389,10 +8391,19 @@ SYSCALL_DEFINE5(perf_event_open,
if (move_group) {
gctx = group_leader->ctx;
mutex_lock_double(&gctx->mutex, &ctx->mutex);
if (gctx->task == TASK_TOMBSTONE) {
err = -ESRCH;
goto err_locked;
}
} else {
mutex_lock(&ctx->mutex);
}
if (ctx->task == TASK_TOMBSTONE) {
err = -ESRCH;
goto err_locked;
}
if (!perf_event_validate_size(event)) {
err = -E2BIG;
goto err_locked;
@ -8563,12 +8574,14 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
WARN_ON_ONCE(ctx->parent_ctx);
mutex_lock(&ctx->mutex);
if (ctx->task == TASK_TOMBSTONE) {
err = -ESRCH;
goto err_unlock;
}
if (!exclusive_event_installable(event, ctx)) {
mutex_unlock(&ctx->mutex);
perf_unpin_context(ctx);
put_ctx(ctx);
err = -EBUSY;
goto err_free;
goto err_unlock;
}
perf_install_in_context(ctx, event, cpu);
@ -8577,6 +8590,10 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
return event;
err_unlock:
mutex_unlock(&ctx->mutex);
perf_unpin_context(ctx);
put_ctx(ctx);
err_free:
free_event(event);
err: