On Wed, 2009-12-30 at 19:28 +0800, Liming Wang wrote:Sorry the changelog is too simple.If the parent has no entry in group_list, child_ctx will not be
allocated, which will lead dereference of a NULL child_ctx.
That changelog sucks.
I didn't find this case.
Best I can make of it is that there is a race where the parent gets his
context instantiated and we manage to get the mutex before the other
thread manages to add the first event.
Then we observe parent_event_ctx but have an empty list.
Is that it?
In that case, would it not be better to change the if (inherited_all)
condition to if (inherited_all && child_ctx) ?
Signed-off-by: Liming Wang <liming.wang@xxxxxxxxxxxxx>
---
kernel/perf_event.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 5b987b4..3664c4b 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -5126,6 +5126,8 @@ int perf_event_init_task(struct task_struct *child)
*/
mutex_lock(&parent_ctx->mutex);
+ if (list_empty(&parent_ctx->group_list))
+ goto exit;
/*
* We dont have to disable NMIs - we are only looking at
* the list, not manipulating it: