Date: Thu, 3 Mar 2016 14:41:38 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Hans Petter Selasky <hps@selasky.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r296320 - in head/sys: kern sys Message-ID: <20160303124138.GS67250@kib.kiev.ua> In-Reply-To: <56D82E45.3090205@selasky.org> References: <201603021846.u22IkHWM010861@repo.freebsd.org> <56D82E45.3090205@selasky.org>
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On Thu, Mar 03, 2016 at 01:29:57PM +0100, Hans Petter Selasky wrote:
> On 03/02/16 19:46, Konstantin Belousov wrote:
> > Modified: head/sys/kern/subr_sleepqueue.c
> > ==============================================================================
> > --- head/sys/kern/subr_sleepqueue.c Wed Mar 2 16:36:24 2016 (r296319)
> > +++ head/sys/kern/subr_sleepqueue.c Wed Mar 2 18:46:17 2016 (r296320)
> > @@ -586,7 +586,8 @@ sleepq_check_timeout(void)
> > * another CPU, so synchronize with it to avoid having it
> > * accidentally wake up a subsequent sleep.
> > */
> > - else if (callout_stop(&td->td_slpcallout) == 0) {
> > + else if (_callout_stop_safe(&td->td_slpcallout, CS_MIGRBLOCK, NULL)
> > + == 0) {
> > td->td_flags |= TDF_TIMEOUT;
> > TD_SET_SLEEPING(td);
> > mi_switch(SW_INVOL | SWT_SLEEPQTIMO, NULL);
>
> The "td_slpcallout" is not drained anywhere, last time I checked. Does
> this change require draining of the td_slpcallout in case the thread
> immediately is exited/destroyed?
callout_stop_safe(CS_MIGRBLOCK) is enough in this case. td_slpcallout
is only reset from the sleepq code, and the fragment you cited is enough
to guarantee that no spurious wakeup of the unrelated time-bound sleep
happens, because TDF_TIMOFAIL flag cannot be cleared after that.
Struct thread memory is type-stable, so callout subsystem never operates
on the freed memory from td_slpcallout.
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