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    SubjectRe: [PATCH 0/3][RFC] Potential fix for leapsecond caused futex issue (v3)
    On 07/03/2012 08:27 AM, Prarit Bhargava wrote:
    >
    > On 07/03/2012 02:09 AM, John Stultz wrote:
    >> On 07/02/2012 07:16 PM, John Stultz wrote:
    >>> NOTE: Some reports have been of a hard hang right at or before
    >>> the leapsecond. I've not been able to reproduce or diagnose
    >>> this, so this fix does not likely address the reported hard
    >>> hangs (unless they end up being connected to the futex/hrtimer
    >>> issue). Please email lkml and me if you experienced this.
    >> Since as noted above, I've seen some sporadic reports of hard hangs. Some seem
    >> connected to the hrtimer problem, where ksoftirq seems to go crazy and cause nmi
    >> watchdog lockups, but others are less clear.
    >>
    >> I wanted to try to provide a way to stress both the kernel's leapsecond code as
    >> well as provide a way for folks to be able to test their application's
    >> robustness in the face of leapsecond inconsistencies.
    >>
    >> Attached is my first attempt at such a test.
    >>
    >> It is designed to be run on a server, where it will schedule a leapsecond every
    >> day at midnight GMT. So every day, while it runs, the server will see a
    >> leapsecond. This allows the the leap second, as well as any suspected timer
    >> related lockups that might happen when the leapsecond is scheduled to be stressed.
    >>
    >> The test also outputs time samples right before, during and after the leapsecond
    >> is applied, so you can watch it happen.
    >>
    >> Also since once a day is a fairly low frequency, if you pass a "-s" to the test,
    >> it will jump the system time forward to 10 seconds right before the scheduled
    >> leapsecond for that day. Allowing a leapsecond to occur every ~13 seconds. This
    >> mode may cause application disruption, as it also causes the system to advance a
    >> day every ~13 seconds.
    >>
    >> The test additionally will note if it observes the hrtimer early expiration
    >> problem that was widely seen over the weekend.
    >>
    >> Hopefully this will provide a mechanism to test and maintain the kernel's
    >> correct behaviour for these rare events, as well as allowing folks to get more
    >> comfortable with leapsecond behaviour and test how it might impact their
    >> applications.
    >>
    >> If anyone who observed a hard hang is able to use this to reproduce the problem,
    >> I'd greatly like to hear about it.
    >> Build instructions are in the test file.
    > Thanks John -- I moved to using this for testing and hit the following
    > softlockup when running latest + your patchset:
    >
    > [ 1084.433362] BUG: soft lockup - CPU#17 stuck for 22s! [leap-a-day:1275]^M
    > [ 1084.440700] Modules linked in: nfs nfs_acl auth_rpcgss fscache lockd sunrpc
    > kvm_intel ixgbe coretemp kvm igb ptp pps_core mdio ioatdma lpc_ich crc32c_intel
    > joydev mfd_core i2c_i801 ghash_clmulni_intel tpm_tis wmi dca sb_edac microcode
    > edac_core pcspkr tpm tpm_bios hid_generic isci libsas scsi_transport_sas mgag200
    > i2c_algo_bit drm_kms_helper ttm drm i2c_core [last unloaded: scsi_wait_scan]^M
    > [ 1084.479183] CPU 17 ^M
    > [ 1084.481568] Modules linked in: nfs nfs_acl auth_rpcgss fscache lockd sunrpc
    > kvm_intel ixgbe coretemp kvm igb ptp pps_core mdio ioatdma lpc_ich crc32c_intel
    > joydev mfd_core i2c_i801 ghash_clmulni_intel tpm_tis wmi dca sb_edac microcode
    > edac_core pcspkr tpm tpm_bios hid_generic isci libsas scsi_transport_sas mgag200
    > i2c_algo_bit drm_kms_helper ttm drm i2c_core [last unloaded: scsi_wait_scan]^M
    > [ 1084.520061] ^M
    > [ 1084.521740] Pid: 1275, comm: leap-a-day Not tainted 3.5.0-rc4+ #1 Intel
    > Corporation S2600CP/S2600CP^M
    > [ 1084.531860] RIP: 0010:[<ffffffff810b3d57>] [<ffffffff810b3d57>]
    > smp_call_function_many+0x1f7/0x260^M

    Hrmm. Can you run:
    $ gdb --eval-command "list *0xffffffff810b3d57" ./vmlinux

    In the root kernel source directory where you saw this?

    > [ 1084.541962] RSP: 0018:ffff88042769fdf8 EFLAGS: 00000202^M
    > [ 1084.547891] RAX: 0000000000000080 RBX: 0000000000000292 RCX: 0000000000000020^M
    > [ 1084.555858] RDX: 0000000000000080 RSI: 0000000000000080 RDI: 0000000000000292^M
    > [ 1084.563826] RBP: ffff88042769fe48 R08: ffffffff81cd7200 R09: 0000000000000080^M
    > [ 1084.571790] R10: ffff88042f7342f0 R11: 0000000000000216 R12: ffffffff8137cd43^M
    > [ 1084.579758] R13: ffff88042769fd88 R14: 0000000000000292 R15: ffff88042769fda8^M
    > [ 1084.587727] FS: 00007fba8d48b740(0000) GS:ffff88042f720000(0000)
    > knlGS:0000000000000000^M
    > [ 1084.596758] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033^M
    > [ 1084.603174] CR2: 0000003d72e18c48 CR3: 0000000415d66000 CR4: 00000000000407e0^M
    > [ 1084.611141] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000^M
    > [ 1084.619120] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400^M
    > [ 1084.627092] Process leap-a-day (pid: 1275, threadinfo ffff88042769e000, task
    > ffff880425fd1720)^M
    > [ 1084.636694] Stack:^M
    > [ 1084.638950] 0000000000000003 0100000000000019 0000000000000000
    > ffffffff8107e960^M
    > [ 1084.647211] ffff88042769fe58 ffff88042769ff58 ffffffff8107e960
    > 0000000000000000^M
    > [ 1084.655479] 0000000000000000 0000000000000000 ffff88042769fe58
    > ffffffff810b3f12^M
    > [ 1084.663723] Call Trace:^M
    > [ 1084.666466] [<ffffffff8107e960>] ? hrtimer_wakeup+0x30/0x30^M
    > [ 1084.672784] [<ffffffff8107e960>] ? hrtimer_wakeup+0x30/0x30^M
    > [ 1084.679107] [<ffffffff810b3f12>] smp_call_function+0x22/0x30^M
    > [ 1084.685530] [<ffffffff810b3f78>] on_each_cpu+0x28/0x70^M
    > [ 1084.691371] [<ffffffff8107ec1c>] do_clock_was_set+0x1c/0x30^M
    > [ 1084.697691] [<ffffffff8107f005>] clock_was_set+0x55/0x60^M
    > [ 1084.703732] [<ffffffff810a6a23>] do_settimeofday+0xd3/0xe0^M
    > [ 1084.709971] [<ffffffff8105f4e5>] do_sys_settimeofday+0xb5/0x110^M
    > [ 1084.716677] [<ffffffff8105f5c3>] sys_settimeofday+0x83/0xb0^M
    > [ 1084.723012] [<ffffffff8160f129>] system_call_fastpath+0x16/0x1b^M
    > [ 1084.729782] Code: f7 ff 15 95 89 b6 00 80 7d bf 00 0f 84 9c fe ff ff 41 f6 47
    > 20 01 0f 84 91 fe ff ff 0f 1f 84 00 00 00 00 00 f3 90 41 f6 47 20 01 <75> f7 e9
    > 7b fe ff ff 66 90 4c 89 e2 4c 89 ee 89 df e8 53 8b 21 ^M
    >
    > I'm taking a look now ... I'm not sure I believe the hrtimer_wakeup() calls on
    > the stack.

    Hrm. Can you sysrq-t the box to see what the other cores are doing?

    thanks
    -john



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