Date: Sun, 7 Jul 2002 16:42:59 -0700 (PDT) From: Don Lewis <dl-freebsd@catspoiler.org> To: current@FreeBSD.ORG Subject: "pipe mutex" vs. "sigio lock" lock order reversal Message-ID: <200207072343.g67Nhs0M024152@gw.catspoiler.org>
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This error showed up in my logs this morning while I was building some
ports on a uni-processor box. I'm running a version of -current from
July 7 about 1 AM PDT.
Jul 7 07:47:09 scratch kernel: lock order reversal
Jul 7 07:47:09 scratch kernel: 1st 0xcabf7980 pipe mutex (pipe mutex) @ /usr/src/sys/kern/sys_pipe.c:451
Jul 7 07:47:09 scratch kernel: 2nd 0xc0474300 sigio lock (sigio lock) @ /usr/src/sys/kern/kern_sig.c:2113
I don't understand all the new locking stuff in -current, but it looks
to me like maybe there should be a PIPE_UNLOCK()/PIPE_LOCK() wrapper
around the following code in sys_pipe.c since a SIGIO could happen
during the msleep().
/*
* Handle non-blocking mode operation or
* wait for more data.
*/
if (fp->f_flag & FNONBLOCK) {
error = EAGAIN;
} else {
rpipe->pipe_state |= PIPE_WANTR;
if ((error = msleep(rpipe, PIPE_MTX(rpipe),
PRIBIO | PCATCH,
"piperd", 0)) == 0)
error = pipelock(rpipe, 1);
}
if (error)
goto unlocked_error;
I don't see a way for the locks to be asserted in the opposite order,
though I suppose there might be a case of PROC_LOCK() followed by
PIPE_LOCK() that would conflict with SIGIO_LOCK() followed by
PROC_LOCK().
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