Date: Wed, 1 Aug 2012 15:05:03 +0100 From: Attilio Rao <attilio@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-stable@freebsd.org Subject: Re: [stable 9] panic on reboot: ipmi_wd_event() Message-ID: <CAJ-FndBULaW_NYbJXLY83tfVk5iDzROKG_WGpL8YC6FXZ7=k6w@mail.gmail.com> In-Reply-To: <201208010853.11447.jhb@freebsd.org> References: <1342742294.2656.24.camel@powernoodle.corp.yahoo.com> <201207311634.24169.jhb@freebsd.org> <CAJ-FndC3pyfJNJBZMZEW9WGs7yA=xeAD2vMyuEeJjELcLOVbOA@mail.gmail.com> <201208010853.11447.jhb@freebsd.org>
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On 8/1/12, John Baldwin <jhb@freebsd.org> wrote: > On Tuesday, July 31, 2012 4:51:19 pm Attilio Rao wrote: >> On 7/31/12, John Baldwin <jhb@freebsd.org> wrote: >> > On Thursday, July 19, 2012 7:58:14 pm Sean Bruno wrote: >> >> Working on the Dell R420 today, got most of it working, even the >> >> broadcom ethernet cards! However, I get the following when I reboot >> >> the >> >> system: >> >> >> >> Syncing disks, vnodes remaining...4 Sleeping thread (tid 100107, pid >> >> 9) >> >> owns a non-sleepable lock >> >> KDB: stack backtrace of thread 100107: >> >> sched_switch() at sched_switch+0x19f >> >> mi_switch() at mi_switch+0x208 >> >> sleepq_switch() at sleepq_switch+0xfc >> >> sleepq_wait() at sleepq_wait+0x4d >> >> _sleep() at _sleep+0x3f6 >> >> ipmi_submit_driver_request() at ipmi_submit_driver_request+0x97 >> >> ipmi_set_watchdog() at ipmi_set_watchdog+0xb1 >> >> ipmi_wd_event() at ipmi_wd_event+0x8f >> >> kern_do_pat() at kern_do_pat+0x10f >> >> sched_sync() at sched_sync+0x1ea >> >> fork_exit() at fork_exit+0x135 >> >> fork_trampoline() at fork_trampoline+0xe >> > >> > Hmmm, the watchdog pat should probably happen without holding locks if >> > possible. This is related to the IPMI watchdog being special and >> > wanting >> > to schedule a thread to work. >> >> The watchdog pat without the locks is not easy to do because we >> register the watchdog callbacks in eventhandlers, which are indeed >> locked (and you may also end up racing against watchdog detach, if you >> don't use any lock at all). > > No, eventhandlers go through several hoops to not hold any locks while > the eventhandler functions are running. It seems in this case that a > lock is held in a higher layer (sched_sync()) and that is what I was > talking about. Yes, it is the 'sync_mtx' that is held. Something like this No, EVENTHANDLER_INVOKE() acquires eventhandler internal locks. Look at eventhandler_find_list() for details. Attilio -- Peace can only be achieved by understanding - A. Einstein
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