Date: Tue, 17 May 2011 16:39:08 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: cvs-src-old@freebsd.org Subject: cvs commit: src/sys/kern subr_smp.c Message-ID: <201105171639.p4HGdTMP097163@repoman.freebsd.org>
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jhb 2011-05-17 16:39:08 UTC
FreeBSD src repository
Modified files:
sys/kern subr_smp.c
Log:
SVN rev 222032 on 2011-05-17 16:39:08Z by jhb
Fix a race in the SMP rendezvous code. Specifically, the write by the
last CPU to to finish the rendezvous action may become visible to
different CPUs at different times. As a result, the CPU that initiated
the rendezvous may exit the rendezvous and drop the lock allowing another
rendezvous to be initiated on the same CPU or a different CPU. In that
case the exit sentinel may be cleared before all CPUs have noticed causing
those CPUs to hang forever.
Workaround this by using a generation count to notice when this race
occurs and to exit the rendezvous in that case.
The problem was independently diagnosted by mlaier@ and avg@ as well.
Submitted by: neel
Reviewed by: avg, mlaier
Obtained from: NetApp
MFC after: 1 week
Revision Changes Path
1.226 +48 -15 src/sys/kern/subr_smp.c
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