On Tue, Apr 08, 2025 at 02:10:44PM +0800, Xiangyu Chen wrote:
From: Peter Zijlstra peterz@infradead.org
[ Upstream commit 517e6a301f34613bff24a8e35b5455884f2d83d8 ]
Per syzbot it is possible for perf_pending_task() to run after the event is free()'d. There are two related but distinct cases:
- the task_work was already queued before destroying the event;
- destroying the event itself queues the task_work.
The first cannot be solved using task_work_cancel() since perf_release() itself might be called from a task_work (____fput), which means the current->task_works list is already empty and task_work_cancel() won't be able to find the perf_pending_task() entry.
The simplest alternative is extending the perf_event lifetime to cover the task_work.
The second is just silly, queueing a task_work while you know the event is going away makes no sense and is easily avoided by re-arranging how the event is marked STATE_DEAD and ensuring it goes through STATE_OFF on the way down.
Reported-by: syzbot+9228d6098455bb209ec8@syzkaller.appspotmail.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Tested-by: Marco Elver elver@google.com [ Discard the changes in event_sched_out() due to 5.10 don't have the commit: 97ba62b27867 ("perf: Add support for SIGTRAP on perf events") and commit: ca6c21327c6a ("perf: Fix missing SIGTRAPs") ] Signed-off-by: Xiangyu Chen xiangyu.chen@windriver.com Signed-off-by: He Zhe zhe.he@windriver.com
Verified the build test.
You missed all of the fix-up patches for this commit that happened after it, fixing memory leaks and the like. So if we applied this, we would have more bugs added to the tree than fixed :(
ALWAYS check for follow-on fixes.
I'll go drop this.
greg k-h