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

    Regards
    --
    Maciej Rutecki
    http://www.maciek.unixy.pl
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