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.
Reviewed-by: Alexander Shishkin <alexander.shish...@linux.intel.com>
Tested-by: Alexander Shishkin <alexander.shish...@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
kernel/events/core.c | 35 ++++++++++++++++++++++++++---------
1 file changed, 26 insertions(+), 9 deletions(-)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2158,13 +2158,15 @@ perf_install_in_context(struct perf_even
*/
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
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
return event;
+err_unlock:
+ mutex_unlock(&ctx->mutex);
+ perf_unpin_context(ctx);
+ put_ctx(ctx);
err_free:
free_event(event);
err:
