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Message-ID: <20230211175948.GK4163@brightrain.aerifal.cx>
Date: Sat, 11 Feb 2023 12:59:49 -0500
From: Rich Felker <dalias@...c.org>
To: Alexey Izbyshev <izbyshev@...ras.ru>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH] mq_notify: fix close/recv race on failure path
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? 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?
Rich
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