Date: Thu, 21 May 2009 16:11:04 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: John Baldwin <jhb@freebsd.org> Cc: Attilio Rao <attilio@freebsd.org>, Kostik Belousov <kostikbel@gmail.com>, svn-src-all@freebsd.org, src-committers@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r192535 - head/sys/kern Message-ID: <alpine.BSF.2.00.0905211610140.18790@fledge.watson.org> In-Reply-To: <200905210942.35555.jhb@freebsd.org> References: <200905211322.n4LDM73t067924@svn.freebsd.org> <20090521132641.GJ1927@deviant.kiev.zoral.com.ua> <3bbf2fe10905210629p46c7a204v6863aaba77354462@mail.gmail.com> <200905210942.35555.jhb@freebsd.org>
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On Thu, 21 May 2009, John Baldwin wrote: >>>> Move the M_WAITOK flag in notify() into an M_NOWAIT one in order to > match >>>> the behaviour alredy present with the further malloc() call in >>>> devctl_notify(). >>>> This fixes a bug in the CAM layer where the camisr handler finished to >>>> call camperiphfree() (and subsequently destroy_dev() resulting in a new >>>> dev notify) while the xpt lock is held. >>> This is wrong. You cannot call destroy_dev() while holding any mutex. >>> Taking this into account, it makes no sense to use M_NOWAIT in notify(). >> >> As long as devctl_notify() also calls M_NOWAIT and if not available skips >> "silently" it just does the same thing, I think this approach is more >> consistent. >> >> It remains, though, the fact to fix CAM when calling destroy_dev(). Maybe >> we should add a witness_warn() there? > > I agree with kib, this should be reverted and CAM fixed instead. I also > agree that M_NOWAIT use should be limited where possible. devctl_notify() probably needs to grow a sleepable flag, or perhaps we need two variations, one that can sleep. Robert N M Watson Computer Laboratory University of Cambridge
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