Date: Thu, 21 May 2009 08:54:01 -0700 From: Scott Long <scottl@samsco.org> To: "M. Warner Losh" <imp@bsdimp.com> Cc: src-committers@FreeBSD.org, jhb@FreeBSD.org, svn-src-all@FreeBSD.org, attilio@FreeBSD.org, svn-src-head@FreeBSD.org, rwatson@FreeBSD.org, kostikbel@gmail.com Subject: Re: svn commit: r192535 - head/sys/kern Message-ID: <4A157919.7040103@samsco.org> In-Reply-To: <20090521.094100.70797067.imp@bsdimp.com> References: <3bbf2fe10905210629p46c7a204v6863aaba77354462@mail.gmail.com> <200905210942.35555.jhb@freebsd.org> <alpine.BSF.2.00.0905211610140.18790@fledge.watson.org> <20090521.094100.70797067.imp@bsdimp.com>
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M. Warner Losh wrote: > In message: <alpine.BSF.2.00.0905211610140.18790@fledge.watson.org> > Robert Watson <rwatson@FreeBSD.org> writes: > : 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. > > devctl_notify() has expanded well beyond its original needs. Having > an extra case for sleeping is the wrong way to solve this problem. > Really. We're adding hacks on hacks on hacks here and we need to step > back and think. > > I specifically didn't put in CDEV notifications into devd when I > originally did it because one can get the same notification via > kevents on /dev. Maybe the right answer is to remove this stuff > entirely and update devd to do that instead? It isn't a lot of code, > and should provide equivalent functionality without needing to change > the rules of the game when it comes to destroy_dev(). Especially this > close to the code slush... > > Comments? > > Warner Very much in agreement here. I would also love to have destroy_dev() and make_dev() be locking-neutral. Having sleepable locks in leaf APIs is unpleasant for consumers of those APIs. Scott
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