Messages in this thread | | | Date | Tue, 2 Sep 2014 09:08:48 -0700 | Subject | Re: Race condition in HR timers that cause double insertion and hard lockup -- all latest versions | From | Linus Torvalds <> |
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On Tue, Sep 2, 2014 at 8:45 AM, Itzcak Pechtalt <itzcak@flashnetworks.com> wrote: > > I opened a bug in https://bugzilla.kernel.org/show_bug.cgi?id=83601 for this subject with full description. > There is also a short fix patch for kernel/hrtimer.c file. > Even if this bug occurs rary, however it resolves system hard lockup option.
The patch is whitespace-damaged, but with a small oneliner like this that doesn't much matter (the timer files moved to kernel/time/ during this merge window, so the patch wouldn't apply as-is anyway).
It needs a sign-off (see Documentation/SubmittingPatches), but even more importantly it needs to go to the right people for double-checking.
But the patch is more broken than whitespace and even lack of sign-off. It cannot even have compiled. I'm assuming "timer_state" was intended to be "timer->state". Also, every caller but one already has "HRTIMER_STATE_CALLBACK" set unconditionally or to the old state in "newstate", so I suspect if this patch is the real fix (which I'll leave for Thomas to comment more on), afaik the actual problem can only happen through migrate_hrtimer_list() which uconditionally sets the whole state to HRTIMER_STATE_MIGRATE.
Thomas? Leaving damaged patch quoted below.
Linus
> I suspect that it was targeted by mistake to not active list (timers_realtime-clock@kernel-bugs.osdl.org). > Following is the fix patch based on kernel 3.16.1 (just simple): > diff -uNr a/kernel/hrtimer.c b/kernel/hrtimer.c > --- a/kernel/hrtimer.c 2014-08-31 20:59:52.177452123 +0300 > +++ b/kernel/hrtimer.c 2014-08-31 21:02:14.972166540 +0300 > @@ -941,7 +941,7 @@ > if (!timerqueue_getnext(&base->active)) > base->cpu_base->active_bases &= ~(1 << base->index); > out: > - timer->state = newstate; > + timer->state = (newstate | (timer_state & HRTIMER_STATE_CALLBACK)); > } > > /* > > Is there a chance for this patch fix to insert into next kernel release? > > Thanks > > Itzcak Pechtalt >
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