Date: Sun, 30 Sep 2012 13:50:07 GMT From: Andriy Gapon <avg@FreeBSD.org> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/172166: Deadlock in the networking code, possible due to a bug in the SCHED_ULE Message-ID: <201209301350.q8UDo7nY045000@freefall.freebsd.org>
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The following reply was made to PR kern/172166; it has been noted by GNATS. From: Andriy Gapon <avg@FreeBSD.org> To: bug-followup@FreeBSD.org, eugen@eg.sd.rdtc.ru Cc: Subject: Re: kern/172166: Deadlock in the networking code, possible due to a bug in the SCHED_ULE Date: Sun, 30 Sep 2012 16:44:09 +0300 on 30/09/2012 16:42 Andriy Gapon said the following: > on 30/09/2012 14:54 Andriy Gapon said the following: >> >> It looks like CPUs 0 - 4 are idle, but CPU 5 has load of three. >> One of those threads is the syslogd thread that holds the lock, but the >> currently running thread is 'ipmi0: kcs' thread with tid 100118. >> It would interesting to examine what it is doing. >> > > Looks like the kcs busy loops in here: kcs_loop -> kcs_read_byte -> > kcs_wait_for_obf. > Since this is a 6-CPU machine, steal threshold is set to 3 so other CPUs don't > try to take any work from CPU5. Not sure if this is smart actually. Maybe it > would make sense to have a lower threshold or to allow stealing of real-time > threads at a lower threshold. > > Since the kcs thread is a kernel thread with real-time priority (68) it doesn't > allow any other lower priority thread to run while it's not sleeping. > > Also, it looks like rwlock does not take care to propagate waiters' priorities > in all cases. Maybe priority propagation could have helped here, but not sure... > In any case, the original trigger for this problem seems to be something in IPMI that keeps that thread running. -- Andriy Gapon
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