On Mon, 29 Mar 2021 at 16:27, Oleg Nesterov oleg@redhat.com wrote:
On 03/29, Peter Zijlstra wrote:
On Thu, Mar 25, 2021 at 09:14:39AM +0100, Marco Elver wrote:
@@ -6395,6 +6395,13 @@ static void perf_sigtrap(struct perf_event *event) { struct kernel_siginfo info;
- /*
- This irq_work can race with an exiting task; bail out if sighand has
- already been released in release_task().
- */
- if (!current->sighand)
return;This is racy. If "current" has already passed exit_notify(), current->parent can do release_task() and destroy current->sighand right after the check.
Urgh.. I'm not entirely sure that check is correct, but I always forget the rules with signal. It could be we ought to be testing PF_EXISTING instead.
Agreed, PF_EXISTING check makes more sense in any case, the exiting task can't receive the signal anyway.
So, per off-list discussion, it appears that I should ask to clarify: PF_EXISTING or PF_EXITING?
It appears that PF_EXISTING is what's being suggested, whereas it has not been mentioned anywhere, nor are its semantics clear. If it is not simply the negation of PF_EXITING, what are its semantics? And why do we need it in the case here (instead of something else that already exists)?
Thanks, -- Marco