Date: Thu, 23 Oct 2014 12:39:39 -0700 From: Adrian Chadd <adrian@freebsd.org> To: =?UTF-8?Q?Edward_Tomasz_Napiera=C5=82a?= <trasz@freebsd.org> Cc: "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, Mateusz Guzik <mjg@freebsd.org>, John Baldwin <jhb@freebsd.org> Subject: Re: svn commit: r273549 - head/sys/kern Message-ID: <CAJ-Vmo=teX0ggxDkjErA%2B_TwddedOsyeYXmkXv5pgB44d7ikBA@mail.gmail.com> In-Reply-To: <20E7F407-9DC5-4A59-BC1C-7B868C31EF52@FreeBSD.org> References: <201410231535.s9NFZlbn002656@svn.freebsd.org> <201410231438.09220.jhb@freebsd.org> <20E7F407-9DC5-4A59-BC1C-7B868C31EF52@FreeBSD.org>
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Please back this out; it looks like the lock is protecting sf_si. -adrian On 23 October 2014 11:45, Edward Tomasz Napiera=C5=82a <trasz@freebsd.org> = wrote: > Dnia 23 pa=C5=BA 2014 o godz. 20:38 John Baldwin <jhb@freebsd.org> napisa= =C5=82(a): > >>> On Thursday, October 23, 2014 11:35:47 am Mateusz Guzik wrote: >>> Author: mjg >>> Date: Thu Oct 23 15:35:47 2014 >>> New Revision: 273549 >>> URL: https://svnweb.freebsd.org/changeset/base/273549 >>> >>> Log: >>> Avoid taking the lock in selfdfree when not needed. >>> >>> Modified: >>> head/sys/kern/sys_generic.c >>> >>> Modified: head/sys/kern/sys_generic.c >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D >>> --- head/sys/kern/sys_generic.c Thu Oct 23 15:16:40 2014 (r273548= ) >>> +++ head/sys/kern/sys_generic.c Thu Oct 23 15:35:47 2014 (r273549= ) >>> @@ -1600,10 +1600,11 @@ static void >>> selfdfree(struct seltd *stp, struct selfd *sfp) >>> { >>> STAILQ_REMOVE(&stp->st_selq, sfp, selfd, sf_link); >>> - mtx_lock(sfp->sf_mtx); >>> - if (sfp->sf_si) >>> + if (sfp->sf_si !=3D NULL) { >>> + mtx_lock(sfp->sf_mtx); >>> TAILQ_REMOVE(&sfp->sf_si->si_tdlist, sfp, sf_threads); >>> - mtx_unlock(sfp->sf_mtx); >>> + mtx_unlock(sfp->sf_mtx); >>> + } >>> uma_zfree(selfd_zone, sfp); >> >> How do you ensure that the value you read for sf_si here is up to date? = In >> particular, if a thread is selecting on multiple fds and one awakens it, >> another fd can invoke selwakeup() while the thread is in seltdclear(). >> In that case, you might see a stale value of sf_si and not realize it is >> cleared by the selwakeup() after you get the lock and you will invoke >> TAILQ_REMOVE an extra time. > > FWIW, I've just hit a panic in selfdfree(). > >
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