Date: Thu, 05 Jul 2001 18:00:24 -0700 (PDT) From: John Baldwin <jhb@FreeBSD.org> To: "Justin T. Gibbs" <gibbs@scsiguy.com> Cc: Doug Rabson <dfr@nlsystems.com>, Matthew Jacob <mjacob@feral.com>, Matt Dillon <dillon@earth.backplane.com>, cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org, Jake Burkholder <jake@FreeBSD.org>, Alfred Perlstein <bright@sneakerz.org> Subject: Re: cvs commit: src/sys/sys systm.h condvar.h src/sys/kern kern_ Message-ID: <XFMail.010705180024.jhb@FreeBSD.org> In-Reply-To: <200107052228.f65MSeU64741@aslan.scsiguy.com>
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On 05-Jul-01 Justin T. Gibbs wrote: >>It happens with SMP, too, not just preemption. The calls are an optimization >>to avoid problems with releasing the lock after the wakeup. The contention >>can be avoided if we release the lock before calling wakeup(), but doing that >>leaves a window open for another CPU to alter the data that the lock protects >>possibly invalidating the wakeup that then gets sent. > > This window exists anyway. The locked mutex it not passed to the woken > up thread, so there will always be a race between the woken up thread > acquiring the mutex and some other thread on some other CPU acquiring it > first and making the wakeup invalid. Ok, then releasing the lock prior to wakeup/cv_foo is fine with me. -- John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/ PGP Key: http://www.baldwin.cx/~john/pgpkey.asc "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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