Re: [BUG] Soft-lockup during cpu-hotplug in VFS callpaths

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

On 09/01/2011 12:10 AM, Maciej Rutecki wrote:
> On środa, 24 sierpnia 2011 o 15:44:55 Srivatsa S. Bhat wrote:
>> Hi,
>>
>> While running stressful cpu hotplug tests along with kernel compilation
>> running in background, soft-lockups are detected on multiple CPUs.
>> Sometimes this also leads to hard lockups and kernel panic.
>> All the soft-lockups seem to occur at vfsmount_lock_local_cpu() or other
>> VFS callpaths.
>>
>>
>> [37108.410813] BUG: soft lockup - CPU#5 stuck for 22s! [cc1:29669]
>> <snip>
>> [37108.694781] Call Trace:
>> [37108.697306]  [<ffffffff81199e70>] ?
>> vfsmount_lock_local_lock_cpu+0x70/0x70 [37108.704258] 
>> [<ffffffff81187cb5>] path_init+0x315/0x400
>> [37108.709558]  [<ffffffff8127c398>] ? __raw_spin_lock_init+0x38/0x70
>> [37108.715812]  [<ffffffff8118961c>] path_openat+0x8c/0x3f0
>> [37108.721203]  [<ffffffff81012129>] ? sched_clock+0x9/0x10
>> [37108.726597]  [<ffffffff8109416d>] ? sched_clock_cpu+0xcd/0x110
>> [37108.732508]  [<ffffffff810a178d>] ? trace_hardirqs_off+0xd/0x10
>> [37108.738498]  [<ffffffff8109421f>] ? local_clock+0x6f/0x80
>> [37108.743970]  [<ffffffff81189a99>] do_filp_open+0x49/0xa0
>> [37108.749362]  [<ffffffff811982f3>] ? alloc_fd+0xc3/0x210
>> [37108.754665]  [<ffffffff8152584b>] ? _raw_spin_unlock+0x2b/0x40
>> [37108.760575]  [<ffffffff811982f3>] ? alloc_fd+0xc3/0x210
>> [37108.765875]  [<ffffffff81179607>] do_sys_open+0x107/0x1e0
>> [37108.771352]  [<ffffffff810d610f>] ? audit_syscall_entry+0x1bf/0x1f0
>> [37108.777695]  [<ffffffff81179720>] sys_open+0x20/0x30
>> [37108.782741]  [<ffffffff8152e202>] system_call_fastpath+0x16/0x1b
>>
>> Kernel version: 3.0.1, 3.0.3
>> Hardware: Dual socket quad-core hyper-threaded Intel x86 machine
>> Scenario:
>> (a) Stressful cpu hotplug tests + kernel compilation
>>
>> (b) IRQ balancing had been disabled and all the IRQs  were made to be
>>     routed to CPU 0 (except the ones that couldn't be routed).
>>
>> (c) Lockdep was enabled during kernel configuration.
>>
>> Steps (b) and (c) were done to dig deeper into the issue. However the same
>> issue was observed by just doing step (a).
>>
>> Definitely there seems to be a race condition occurring here, because this
>> issue is hit after sometime, after starting the tests. And the time it
>> takes to hit the issue increases as we increase the number of debug print
>> statements. In some cases (especially when the number of debug print
>> statements were quite high), the stress on the machine had to be increased
>> in order to hit the issue within measurable time. In my tests, a maximum
>> of about 2 to 2.5 hours was sufficient, to hit this bug.
>>
>> Please find the console log attached with this mail.
>>
>> Any ideas on how to go about fixing this bug?
> 
> It is a regression?

Hi Maciej,

Thank you for taking a look.
Yes, it seems to be a regression. I tested out kernel 2.6.39.3 with similar test cases
for quite a long time, and it did not hit any soft-lockup issues.

-- 
Regards,
Srivatsa S. Bhat  <srivatsa.bhat@linux.vnet.ibm.com>
Linux Technology Center,
IBM India Systems and Technology Lab