Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [patch V2 3/3] signal: Allow tasks to cache one sigqueue struct | Date | Fri, 12 Mar 2021 22:13:25 +0100 |
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On Fri, Mar 12 2021 at 20:26, Thomas Gleixner wrote: > On Fri, Mar 12 2021 at 17:11, Oleg Nesterov wrote: >> On 03/11, Thomas Gleixner wrote: >>> >>> @@ -456,7 +460,12 @@ static void __sigqueue_free(struct sigqu >>> return; >>> if (atomic_dec_and_test(&q->user->sigpending)) >>> free_uid(q->user); >>> - kmem_cache_free(sigqueue_cachep, q); >>> + >>> + /* Cache one sigqueue per task */ >>> + if (!current->sigqueue_cache) >>> + current->sigqueue_cache = q; >>> + else >>> + kmem_cache_free(sigqueue_cachep, q); >>> } >> >> This doesn't look right, note that __exit_signal() does >> flush_sigqueue(&sig->shared_pending) at the end, after exit_task_sighand() >> was already called. >> >> I'd suggest to not add the new exit_task_sighand() helper and simply free >> current->sigqueue_cache at the end of __exit_signal(). > > Ooops. Thanks for spotting this!
Hrm.
The task which is released is obviously not current, so even if there are still sigqueues in shared_pending then they wont end up in the released tasks sigqueue_cache. They can only ever end up in current->sigqueue_cache.
But that brings my memory back why I had cmpxchg() in the original version. This code runs without current->sighand->siglock held.
So we need READ/WRITE_ONCE() for that on both sides which is sufficient.
Thanks,
tglx
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