On Thursday 21 May 2009 11:41:00 am M. Warner Losh wrote: > In message: <alpine.bsf.2.00.0905211610140.18...@fledge.watson.org> > Robert Watson <rwat...@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?
destroy_dev() is not a good idea to call with a mutex held period. devctl_notify() is the least of one's worries in that case. In general the code holding a mutex over destroy_dev() should be fixed and I think devctl_notify() can be left unchanged. destroy_dev() is a draining operation similar to bus_teardown_intr(), callout_drain(), taskqueue_drain(), if_detach() (which doesn't drain yet, but needs to), etc. One simply cannot hold locks across those operations. -- John Baldwin _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
