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-rw-r--r--kernel/events/core.c28
1 files changed, 25 insertions, 3 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1833bc5a84a7..eba8fb5834ae 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -947,8 +947,18 @@ perf_lock_task_context(struct task_struct *task, int ctxn, unsigned long *flags)
{
struct perf_event_context *ctx;
- rcu_read_lock();
retry:
+ /*
+ * One of the few rules of preemptible RCU is that one cannot do
+ * rcu_read_unlock() while holding a scheduler (or nested) lock when
+ * part of the read side critical section was preemptible -- see
+ * rcu_read_unlock_special().
+ *
+ * Since ctx->lock nests under rq->lock we must ensure the entire read
+ * side critical section is non-preemptible.
+ */
+ preempt_disable();
+ rcu_read_lock();
ctx = rcu_dereference(task->perf_event_ctxp[ctxn]);
if (ctx) {
/*
@@ -964,6 +974,8 @@ retry:
raw_spin_lock_irqsave(&ctx->lock, *flags);
if (ctx != rcu_dereference(task->perf_event_ctxp[ctxn])) {
raw_spin_unlock_irqrestore(&ctx->lock, *flags);
+ rcu_read_unlock();
+ preempt_enable();
goto retry;
}
@@ -973,6 +985,7 @@ retry:
}
}
rcu_read_unlock();
+ preempt_enable();
return ctx;
}
@@ -1950,7 +1963,16 @@ static int __perf_event_enable(void *info)
struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
int err;
- if (WARN_ON_ONCE(!ctx->is_active))
+ /*
+ * There's a time window between 'ctx->is_active' check
+ * in perf_event_enable function and this place having:
+ * - IRQs on
+ * - ctx->lock unlocked
+ *
+ * where the task could be killed and 'ctx' deactivated
+ * by perf_event_exit_task.
+ */
+ if (!ctx->is_active)
return -EINVAL;
raw_spin_lock(&ctx->lock);
@@ -7465,7 +7487,7 @@ inherit_task_group(struct perf_event *event, struct task_struct *parent,
* child.
*/
- child_ctx = alloc_perf_context(event->pmu, child);
+ child_ctx = alloc_perf_context(parent_ctx->pmu, child);
if (!child_ctx)
return -ENOMEM;