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

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