Date: Thu, 23 Oct 2014 20:45:13 +0200 From: =?utf-8?Q?Edward_Tomasz_Napiera=C5=82a?= <trasz@FreeBSD.org> To: John Baldwin <jhb@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> Subject: Re: svn commit: r273549 - head/sys/kern Message-ID: <20E7F407-9DC5-4A59-BC1C-7B868C31EF52@FreeBSD.org> In-Reply-To: <201410231438.09220.jhb@freebsd.org> References: <201410231535.s9NFZlbn002656@svn.freebsd.org> <201410231438.09220.jhb@freebsd.org>
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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 >>=20 >> Log: >> Avoid taking the lock in selfdfree when not needed. >>=20 >> Modified: >> head/sys/kern/sys_generic.c >>=20 >> 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); >=20 > How do you ensure that the value you read for sf_si here is up to date? I= n=20 > 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=20= > 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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