From owner-svn-src-all@FreeBSD.ORG Thu Oct 23 18:38:30 2014 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id CBA34EA2; Thu, 23 Oct 2014 18:38:30 +0000 (UTC) Received: from bigwig.baldwin.cx (bigwig.baldwin.cx [IPv6:2001:470:1f11:75::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id A40A0D3C; Thu, 23 Oct 2014 18:38:30 +0000 (UTC) Received: from jhbbsd.localnet (unknown [209.249.190.124]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id B9B0FB9B9; Thu, 23 Oct 2014 14:38:29 -0400 (EDT) From: John Baldwin To: Mateusz Guzik Subject: Re: svn commit: r273549 - head/sys/kern Date: Thu, 23 Oct 2014 14:38:09 -0400 User-Agent: KMail/1.13.5 (FreeBSD/8.4-CBSD-20140415; KDE/4.5.5; amd64; ; ) References: <201410231535.s9NFZlbn002656@svn.freebsd.org> In-Reply-To: <201410231535.s9NFZlbn002656@svn.freebsd.org> MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <201410231438.09220.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Thu, 23 Oct 2014 14:38:29 -0400 (EDT) Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 23 Oct 2014 18:38:30 -0000 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 > ============================================================================== > --- 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 != 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. -- John Baldwin