Date: Wed, 14 Jul 2004 12:05:39 -0700 From: Nate Lawson <nate@root.org> To: Doug Rabson <dfr@nlsystems.com> Cc: src-committers@FreeBSD.org Subject: Re: cvs commit: src/sys/kern kern_event.c src/sys/sys eventvar.h Message-ID: <40F58403.5020600@root.org> In-Reply-To: <200407142001.25615.dfr@nlsystems.com> References: <Pine.NEB.3.96L.1040714145151.56002C-100000@fledge.watson.org> <200407142001.25615.dfr@nlsystems.com>
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Doug Rabson wrote: > On Wednesday 14 July 2004 19:56, Robert Watson wrote: >>On Wed, 14 Jul 2004, Alfred Perlstein wrote: >>>I can fix this by setting a "sigio in progress" on the kqeue and >>>not calling pgsigio() while one is in progress. >> >>My worry is the inter-subsystem calling. We often call KNOTE() while >>holding existing locks in the calling subsystem that we can't drop. >>Generally, kqueue is a leaf node subsystem in that it's called from >>many places under many circumstances, and needs to not disrupt the >>calling state by doing "weird things". What's there before your >>change is not too disruptive/weird; afterwards, we call into the body >>of the process signalling code which requires additional process >>locks. Note that there are other paths to the same suffering: if any >>other signal is delivered to a process that's monitoring for signals >>with kqueue causing a sigio, you're still recursing into the signal >>subsystem. > > Seems to me that the best thing to do is to defer the psigio() to a > taskqueue that will run in a simpler locking environment. In fact, the AIO task threads already provide a convenient context for this. -- -Nate
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