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Message-ID: <d7af86915e9eb431bf2ffbbf66adfb49@ispras.ru>
Date: Sat, 11 Feb 2023 21:08:53 +0300
From: Alexey Izbyshev <izbyshev@...ras.ru>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] mq_notify: fix close/recv race on failure path
On 2023-02-11 20:59, Rich Felker wrote:
> On Sat, Feb 11, 2023 at 08:50:15PM +0300, Alexey Izbyshev wrote:
>> On 2023-02-11 20:13, Markus Wichmann wrote:
>> >On Sat, Feb 11, 2023 at 10:06:03AM -0500, Rich Felker wrote:
>> >>--- a/src/thread/pthread_detach.c
>> >>+++ b/src/thread/pthread_detach.c
>> >>@@ -5,8 +5,12 @@ static int __pthread_detach(pthread_t t)
>> >> {
>> >> /* If the cas fails, detach state is either already-detached
>> >> * or exiting/exited, and pthread_join will trap or cleanup. */
>> >>- if (a_cas(&t->detach_state, DT_JOINABLE, DT_DETACHED) !=
>> >>DT_JOINABLE)
>> >>+ if (a_cas(&t->detach_state, DT_JOINABLE, DT_DETACHED) !=
>> >>DT_JOINABLE) {
>> >>+ int cs;
>> >>+ __pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
>> >> return __pthread_join(t, 0);
>> > ^^^^^^ I think you forgot to rework this.
>> >>+ __pthread_setcancelstate(cs, 0);
>> >>+ }
>> >> return 0;
>> >> }
>> >>
>> >
>> >I see no other obvious missteps, though.
>> >
>> Same here, apart from this and misspelled "pthred_detach" in the
>> commit message, the patches look good to me.
>>
>> Regarding the POSIX requirement to run sigev_notify_function in the
>> context of a detached thread, while it's possible to observe the
>> wrong detachstate for a short while via pthread_getattr_np after
>> these patches, I'm not sure there is a standard way to do that. Even
>> if it exists, this minor issue may be not worth caring about.
>
> Would this just be if the notification callback executes before
> mq_notify returns in the parent?
Yes, it seems so.
> I suppose we could have the newly
> created thread do the work of making the syscall, handling the error
> case, detaching itself on success and and reporting back to the
> mq_notify function whether it succeeded or failed via the
> semaphore/args structure. Thoughts on that?
>
Could we just move pthread_detach call to the worker thread to the point
after pthread_cleanup_pop?
Alexey
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