Date: Wed, 7 Jan 2004 19:15:51 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: Don Lewis <truckman@freebsd.org> Cc: shoesoft@gmx.net Subject: Re: sound/pcm/* bugs (was: Re: page fault panic tracked down (selwakeuppri()) - really sound/pcm/*) Message-ID: <20040107184629.H7587@gamplex.bde.org> In-Reply-To: <200401070501.i0751a7E015620@gw.catspoiler.org> References: <200401070501.i0751a7E015620@gw.catspoiler.org>
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On Tue, 6 Jan 2004, Don Lewis wrote: > [... lots of good stuff] > I found another bug, though. Holding a mutex across a malloc() call is > not allowed because malloc() can sleep, and sleeping while holding a > mutex is not allowed. sndbuf_resize() sndbuf_remalloc() both call > malloc() to allocate buffers, and sndbuf_alloc() and sndbuf_setup() call > sndbuf_resize(). The problem is that chn_setblocksize() calls > sndbuf_remalloc() while the channel mutex is held. We can't just unlock > the mutex around the sndbuf_remalloc() call because the channel > interrupt service routine could run while the buffer is being > re-allocated. It would be best if the channel were to be shut down when > re-allocating the buffer. This is likely to be messy since > chn_setblocksize() is called from lots of different places. Er, its an M_NOWAIT malloc(), so it can't sleep. M_WAITOK malloc()s in interrupt handlers would also be bugs, but that is not a problem here for the same reason. There should be more checks for potential sleeps while holding a mutex. Bruce
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