Messages in this thread | | | Date | Sun, 23 Nov 2014 16:42:07 -0500 | From | Chris Mason <> | Subject | Re: New crashes walking proc with Saturday's git |
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On Sun, Nov 23, 2014 at 4:38 PM, Thomas Gleixner <tglx@linutronix.de> wrote: > On Sun, 23 Nov 2014, Chris Mason wrote: >> On Sun, Nov 23, 2014 at 4:05 PM, Thomas Gleixner >> <tglx@linutronix.de> wrote: >> > On Sun, 23 Nov 2014, Chris Mason wrote: >> > > On Sun, Nov 23, 2014 at 11:32 AM, Borislav Petkov >> <bp@alien8.de> wrote: >> > > > On Sun, Nov 23, 2014 at 11:16:51AM -0500, Chris Mason wrote: >> > > > > It must be: >> > > > > >> > > > > commit 6e998916dfe327e785e7c2447959b2c1a3ea4930 >> > > > > Author: Stanislaw Gruszka <sgruszka@redhat.com> >> > > > > Date: Wed Nov 12 16:58:44 2014 +0100 >> > > > > >> > > > > sched/cputime: Fix clock_nanosleep()/clock_gettime() >> > > inconsistency >> > > > > >> > > > > I'll do two runs to confirm, but it's the only related >> patch between >> > > rc5 >> > > > > and >> > > > > now. >> > > >> > > I've adding Ingo and Stanislaw to the cc. With >> > > 6e998916dfe327e785e7c2447959b2c1a3ea4930 reverted, I'm no >> longer >> > > crashing. >> > > >> > > Repeating the stack trace for the new cc list. I see the >> crash with atop >> > > or >> > > similar walkers of /proc racing against exiting programs. >> Given the NULL >> > > rip, >> > > this line from the patch is probably broken, but it really >> feels like we >> > > should be falling over on p->sched_class and not on the >> update_curr func. >> > > >> > > + p->sched_class->update_curr(rq); >> > > >> > > I'm leaving my fork bomb running on two machines with the >> patch reverted >> > > to >> > > make sure. >> > >> > The sched_class instances which do not have update_curr are >> stop_task >> > and idle. Patch below. >> > >> > I'm sure nobody thought about the stats read code path here. >> > >> > [ 1053.759741] [<ffffffff81208348>] do_task_stat+0x8b8/0xb00 >> > >> > do_task_stat(() >> > thread_group_cputime_adjusted() >> > thread_group_cputime() >> > task_cputime() >> > task_sched_runtime() >> > if (task_current(rq, p) && task_on_rq_queued(p)) { >> > update_rq_clock(rq); >> > p->sched_class->update_curr(rq); >> > } >> > >> > Now if the stats are read for a stomp machine task, aka >> 'migration/N' >> > and that task is current on its cpu. Ooops. >> > >> > I added the callback for idle tasks as well for completeness sake. >> >> This does make sense, but it doesn't match with the crash being >> much more >> likely during the fork bomb. The difference is crashing within a >> few hours vs >> crashing within 5 minutes. > > The fork bomb will kick the migration task pretty often into life, so > the probablity of do_task_stat() to hit a running migration thread is > higher than on a normaly loaded machine.
Fair enough, I just had crashes_in_proc == races_with_exit stuck in my head ;) I've got a new xfstests run on the second machine to be sure, but this is definitely better.
-chris
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