Date: Wed, 7 Jul 2010 14:14:42 +0200 From: =?UTF-8?Q?Marius_N=C3=BCnnerich?= <marius@nuenneri.ch> To: Attilio Rao <attilio@freebsd.org> Cc: freebsd-current@freebsd.org, Bryan Venteicher <bryanv@daemoninthecloset.org> Subject: Re: deadlkres() panic Message-ID: <AANLkTilx5SZ8esR8CfF2Z8ulyRtQA8KEPtZQKZR1ZbN5@mail.gmail.com> In-Reply-To: <AANLkTikPaLtElkaNzZ248xHhLUnF758rLPNL0YBdSv76@mail.gmail.com> References: <744734406.21.1277969273426.JavaMail.root@sage.daemoninthecloset.org> <269478215.24.1277969553870.JavaMail.root@sage.daemoninthecloset.org> <AANLkTikPaLtElkaNzZ248xHhLUnF758rLPNL0YBdSv76@mail.gmail.com>
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On Wed, Jul 7, 2010 at 14:01, Attilio Rao <attilio@freebsd.org> wrote: > 2010/7/1 Bryan Venteicher <bryanv@daemoninthecloset.org>: >> On a recent -current, I got the following panic from deadlkres: >> >> Assertion wchan != NULL failed at /usr/src-nfs/sys/kern/subr_sleepqueue.c:680 >> >> Tracing pid 0 tid 100058 td 0xffffff00024bf7a0 >> kdb_enter() at kdb_enter+0x3d >> panic() at panic+0x176 >> sleepq_type() at sleepq_type+0x56 >> deadlkres() at deadlkres+0x224 >> fork_exit() at fork_exit+0x12a >> fork_trampoline() at fork_trampoline+0xe >> --- trap 0, rip = 0, rsp = 0xffffff8074976d30, rbp = 0 --- >> (Hand transcribed, doadump() hung) >> >> deadlkres() came across a TD_IS_SLEEPING()'ing thread that was not a >> sleepqueue (ie, td->td_wchan == NULL). >> >> I don't think this is an invalid state for thread to be in: After adding itself >> to a sleepq and setting a timeout, the thread calls sleepq_timedwait_sig(). >> sleepq_catch_signals() determines there is a signal pending so it removes the >> thread from the sleepq via sleepq_resume_thread(). Returning to >> sleepq_timedwait_sig(), in the call to sleepq_check_timeout(), the thread is >> unable to cancel the timeout because it is already firing (likely waiting on >> thread_lock()). So the thread calls TD_SET_SLEEPING() followed by mi_switch(). >> deadlkres() then picks up thread_lock(), finding td is TD_IS_SLEEPING() && >> !TD_ON_SLEEPQ(). >> >> The attached patch takes care of the panic for me. > > I think that your analysis and patch are both fine and are committed, > along with a small cleanup, as r209761. Thank you both, I guess a had that panic a few days ago. Updating right now.
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