Hi John, * John Stultz (john.stu...@linaro.org) wrote: > On 09/11/2013 08:08 AM, Mathieu Desnoyers wrote: > > Starting from commit 06c017fdd4dc48451a29ac37fc1db4a3f86b7f40 > > "timekeeping: Hold timekeepering locks in do_adjtimex and hardpps" > > (3.10 kernels), the xtime write seqlock is held across calls to > > __do_adjtimex(), which includes a call to notify_cmos_timer(), and hence > > schedule_delayed_work(). > > > > This introduces a side-effect for a set of tracepoints, including mainly > > the workqueue tracepoints: a tracer hooking on those tracepoints and > > reading current time with ktime_get() will cause hard system LOCKUP such > > as: > Oh bummer. I had just worked this issue out the other day: > https://lkml.org/lkml/2013/9/9/476 > > Apparently it was a schroedinbug of sorts. My apologies for time you > spent chasing this down.
No worries. As soon as I've been able to reproduce it on my test box (with serial port), the NMI watchdog had a pretty reasonable explanation for the issue. > My plan is to pull the notify_cmos_timer call to outside of the > timekeeper locking (see the patch at the very end of the mail in the > above link), as well as try to add lockdep support to seqcount/seqlocks > so we can catch these sorts of issues more easily. I just tried your patch, and it indeed seems to fix the lockup I've been experiencing with lttng-modules. Do you plan pushing this fix into master, and submitting it for inclusion into stable 3.10 and stable 3.11 ? I'm planning on dealing with with this issue with a blacklist of kernel versions that will prevent people from building lttng-modules against broken kernels as soon as the patch makes it into those trees. I will reply to the rest of your email separately, so this thread can focus on getting the fix upstream quickly. Thanks! Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
