Date: Fri, 22 Oct 2010 11:56:53 +0200 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-geom@freebsd.org Subject: Re: Hyperactive g_event thread Message-ID: <i9rn51$ec0$1@dough.gmane.org> In-Reply-To: <20101021174301.GA1381@a91-153-123-205.elisa-laajakaista.fi> References: <4C4ED619.7050305@FreeBSD.org> <27237.1280241532@critter.freebsd.dk> <AANLkTi=uRPV2T0=t_1s=Jc4PmBtai=__HqhCtYpiDdTQ@mail.gmail.com> <AANLkTikvV4oymBBA%2B_0zbzd_edS8dRfqqJRODE0989%2Bn@mail.gmail.com> <4C4F171C.9010106@FreeBSD.org> <20101021174301.GA1381@a91-153-123-205.elisa-laajakaista.fi>
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On 10/21/10 19:43, Jaakko Heinonen wrote: > I drafted a patch to use g_eventlock instead to protect against losing > wakeups: > > http://people.freebsd.org/~jh/patches/geom-eventproc-sleep.diff > > Reviews and/or testing will be welcomed. Isn't this sequence: - mtx_unlock(&g_eventlock); wakeup(&g_wait_event); + mtx_unlock(&g_eventlock); too racy? It is possible, especially if something changes in scheduling or the wakeup() implementation, and on single-CPU machines, that the woken thread could run and then encounter the lock not yet released, leading to more lock waiting.help
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