On Thu, Apr 04, 2013 at 06:59:59PM -0700, Guenter Roeck wrote: > On Fri, Apr 05, 2013 at 12:23:30AM +0200, Arkadiusz Miskiewicz wrote: > > On Thursday 14 of March 2013, Arkadiusz Miśkiewicz wrote: > > > Hi. > > > > > > Just hit watchdog related oops in 3.8.3 kernel. Unfortunately photos only. > > > > > > http://ixion.pld-linux.org/~arekm/watchdog-oops-3.8.3/IMG_8942.JPG > > > http://ixion.pld-linux.org/~arekm/watchdog-oops-3.8.3/IMG_8941.JPG > > > > 3.9git from today isn't any better unfortunately: > > > > http://ixion.pld-linux.org/~arekm/watchdog-oops-3.9git.jpg > > > > > > > > oops started after I enabled systemd watchdog functionality. Cannot > > > reproduce easily. > > > > > > watchdog here (thinkpad t400) is: > > > iTCO_wdt: Found a ICH9M-E TCO device (Version=2, TCOBASE=0x1060) > > > > > Wonder if there is a race condition in the watchdog driver: The watchdog device > is opened before watchdog_register_device returns. I suspect systemd waits for > a udev event, or by some other means detects that /dev/watchdog was created, > and opens it immediately. > > I just have no idea where exactly the race condition, if there is one, is > hiding. Or maybe I am completely off track. > I _think_ I understand the sequence of events. - The driver is the first watchdog driver to register. - watchdog_dev_register() gets called and creates the watchdog misc device by calling misc_register(). At that time, the matching character device (/dev/watchdog0) does not yet exist, and old_wdd is not set either. - Userspace gets an event and opens /dev/watchdog - watchdog_open() is called and sets sets wdd = old_wdd, which is still NULL, and tries to dereference it. Bang. If this is the problem, a simple fix would be to set old_wdd before calling misc_register(). Can you test a patch ? Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-watchdog" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
