Re: linux-next: Tree for Feb 4

[Steven Rostedt]

On Thu, 5 Feb 2015 20:25:21 +0100
Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:

> On Thu, Feb 5, 2015 at 7:45 PM, Paul E. McKenney
> <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> > On Thu, Feb 05, 2015 at 10:35:33AM -0800, Dave Hansen wrote:
> >> On 02/05/2015 10:34 AM, Paul E. McKenney wrote:
> >> >> >                               Did I actually need to be
> >> >> > onlining/offlining CPUs to hit the splat that Sedat was reporting?
> >> > Yep, you do need to offline at least one CPU to hit that splat.
> >>
> >> Heh, do we need a debugging mode that will randomly offline/online CPUs? :)
> >
> > For that, kernel/rcu/rcutorture.c and kernel/locking/locktorture.c
> > are your friends.  ;-)
> >
> > The problem is that I only run RCU-relevant combinations of Kconfigs,
> > which means that I missed the ones that Sedat used to find this problem.
> > So I guess it is a good thing that others run -next testing.
> >
> 
> [ Revived by a voltaren resinat pill... ]
> 
> I reverted "x86/mm: Omit switch_mm() tracing for offline CPUs"
> ...and...
> applied "tlb: Don't do trace_tlb_flush() on offline CPUs"
> ...in my build-dir.

Is this Paul's version of the patch or mine? If it is just mine, do you
know if Paul's version triggers this too?

> ( I did not build from scratch but re-invoking make "updated" the
> files touched by Steven's patch, see attached build-log. )
> 
> Unfortunately, the call-trace remains when doing an offlining of cpu1.
> ( It's good to see it's reproducible. )

Was the tracepoint enabled? Or was there some other rcu call that
triggered this. Or would cpu_online(smp_processor_id()) return true at
this point?

-- Steve

> 
> root# echo 0 > /sys/devices/system/cpu/cpu1/online
> 
> [  121.652796] intel_pstate CPU 1 exiting
> [  121.666272]
> [  121.666274] ===============================
> [  121.666274] [ INFO: suspicious RCU usage. ]
> [  121.666277] 3.19.0-rc7-next-20150204.7-iniza-small #4 Not tainted
> [  121.666278] -------------------------------
> [  121.666280] include/trace/events/tlb.h:37 suspicious
> rcu_dereference_check() usage!
> [  121.666281]
> [  121.666281] other info that might help us debug this:
> [  121.666281]
> [  121.666282]
> [  121.666282] RCU used illegally from offline CPU!
> [  121.666282] rcu_scheduler_active = 1, debug_locks = 0
> [  121.666283] no locks held by swapper/1/0.
> [  121.666284]
> [  121.666284] stack backtrace:
> [  121.666287] CPU: 1 PID: 0 Comm: swapper/1 Not tainted
> 3.19.0-rc7-next-20150204.7-iniza-small #4
> [  121.666288] Hardware name: SAMSUNG ELECTRONICS CO., LTD.
> 530U3BI/530U4BI/530U4BH/530U3BI/530U4BI/530U4BH, BIOS 13XK 03/28/2013
> [  121.666293]  0000000000000001 ffff88011a44fe18 ffffffff817e39cd
> 0000000000000011
> [  121.666296]  ffff88011a448290 ffff88011a44fe48 ffffffff810d6af7
> ffff8800d3dfaac0
> [  121.666299]  0000000000000001 ffffffff81d32ce0 0000000000000005
> ffff88011a44fe78
> [  121.666300] Call Trace:
> [  121.666308]  [<ffffffff817e39cd>] dump_stack+0x4c/0x65
> [  121.666313]  [<ffffffff810d6af7>] lockdep_rcu_suspicious+0xe7/0x120
> [  121.666318]  [<ffffffff810b73f9>] idle_task_exit+0x1c9/0x260
> [  121.666322]  [<ffffffff81054c4e>] play_dead_common+0xe/0x50
> [  121.666325]  [<ffffffff81054ca5>] native_play_dead+0x15/0x140
> [  121.666330]  [<ffffffff8102963f>] arch_cpu_idle_dead+0xf/0x20
> [  121.666333]  [<ffffffff810cdb4e>] cpu_startup_entry+0x37e/0x580
> [  121.666336]  [<ffffffff81053e20>] start_secondary+0x140/0x150
> [  121.666744] smpboot: CPU 1 is now offline
> 
> >From rcu point this is now safe?
> But another area (linux-pm?) is still affected?
> I will try to test "vanilla" pm-next if the problem exists with
> intel_pstate as suggested by Rafael.
> Hmmm, not sure how I can get the pm-next code which went into
> next-20150204 as linux-pm.git#linux-next was feeded with new stuff.
> 
> 
> - Sedat -

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