Date: Mon, 10 May 2010 00:27:40 +0200 From: Attilio Rao <attilio@freebsd.org> To: Marius Strobl <marius@alchemy.franken.de> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r206878 - head/sys/kern Message-ID: <l2v3bbf2fe11005091527r7651564eq1b2bdf3e1096b32b@mail.gmail.com> In-Reply-To: <20100509170414.GA35602@alchemy.franken.de> References: <201004192327.o3JNRsK4047856@svn.freebsd.org> <20100509170414.GA35602@alchemy.franken.de>
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2010/5/9 Marius Strobl <marius@alchemy.franken.de>: > On Mon, Apr 19, 2010 at 11:27:54PM +0000, Attilio Rao wrote: >> Author: attilio >> Date: Mon Apr 19 23:27:54 2010 >> New Revision: 206878 >> URL: http://svn.freebsd.org/changeset/base/206878 >> >> Log: >> Fix a deadlock in the shutdown code: >> When performing a smp_rendezvous() or more likely, on amd64 and i386, >> a smp_tlb_shootdown() the caller will end up with the smp_ipi_mtx >> spinlock held, busy-waiting for other CPUs to acknowledge the operation. >> As long as CPUs are suspended (via cpu_reset()) between the active mask >> read and IPI sending there can be a deadlock where the caller will wait >> forever for a dead CPU to acknowledge the operation. >> Please note that on CPU0 that is going to be someway heavier because of >> the spinlocks being disabled earlier than quitting the machine. >> >> Fix this bug by calling cpu_reset() with the smp_ipi_mtx held. >> Note that it is very likely that a saner offline/online CPUs mechanism >> will help heavilly in fixing similar cases as it is likely more bugs >> of this type may arise in the future. >> > > This change causes a hang for me when running an SMP kernel on an > UP machine or an MP machine with SMP disabled as in these cases > smp_ipi_mtx isn't initialized (see mp_start()). The below patch > fixes this for me. Marius, thanks a lot for reporting this. However, I think that a better fix is to always initialize the mutex. Do you think the following patch is fine for you?: http://www.freebsd.org/~attilio/smpipi_fixup.diff Thanks, Attilio -- Peace can only be achieved by understanding - A. Einsteinhelp
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