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    SubjectRe: perf: perf_fuzzer triggers instant reboot
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    On Wed, Sep 24, 2014 at 9:59 PM, Vince Weaver <vincent.weaver@maine.edu> wrote:
    >
    > So I noticed Cong Wang's patch (3577af70a2ce4853d58e57d832e687d739281479)
    > perf: Fix a race condition in perf_remove_from_context()
    >
    > and that sounds a lot like the weird fork()/memory-corruption bug that the
    > fuzzer has been triggering.
    >
    > So I applied that patch alone on top of the 3.17-rc4 kernel that I could
    > reproducibly reboot... and with the patch I can't trigger the problem
    > anymore.
    >
    > Now that just might mean the patch pushed the code around enough so my
    > test doesn't trigger, but there is hope that maybe this fixes things.

    I read this as it fixes your crash as well?

    >
    > Cong Wang, do you have more info on how you came across this bug? And how
    > you tracked down the problem?

    Sure, as I said in the changelog, it is a soft lockup which was triggered on
    dozens of machines here, it is actually pretty straightforward:


    [5108912.562963] BUG: soft lockup - CPU#7 stuck for 22s! [perf:13856]
    [5108912.563173] Modules linked in: netconsole configfs ipv6 bonding
    dm_multipath video sbs sbshc hed acpi_pad acpi_memhotplug acpi_ipmi
    parport_pc lp parport tcp_diag inet_diag ipmi_si ipmi_devintf
    ipmi_msghandler dell_rbu igb dcdbas shpchp i2c_i801 i2c_core iTCO_wdt
    i7core_edac edac_core iTCO_vendor_support ioatdma dca microcode
    [5108912.563198] CPU 7
    [5108912.563199] Modules linked in: netconsole configfs ipv6 bonding
    dm_multipath video sbs sbshc hed acpi_pad acpi_memhotplug acpi_ipmi
    parport_pc lp parport tcp_diag inet_diag ipmi_si ipmi_devintf
    ipmi_msghandler dell_rbu igb dcdbas shpchp i2c_i801 i2c_core iTCO_wdt
    i7core_edac edac_core iTCO_vendor_support ioatdma dca microcode
    [5108912.563216]
    [5108912.563219] Pid: 13856, comm: perf Not tainted 3.4.78 #1 Dell
    Inc. C6100 /0D61XP
    [5108912.563222] RIP: 0010:[<ffffffff810d9a6a>] [<ffffffff810d9a6a>]
    perf_remove_from_context+0x8d/0xb4
    [5108912.563233] RSP: 0018:ffff8809ea39bd48 EFLAGS: 00000202
    [5108912.563235] RAX: 000000000000006d RBX: ffffffff810d6dcc RCX:
    0000000000000000
    [5108912.563237] RDX: ffff88123fc8006d RSI: ffffffff810d6dcc RDI:
    ffff8808f8541c0c
    [5108912.563239] RBP: ffff8809ea39bd88 R08: 0000000000000001 R09:
    0000000000000000
    [5108912.563241] R10: ffff8809abf95610 R11: ffff880a3a6c331c R12:
    0000000000000000
    [5108912.563243] R13: 00000000000000ef R14: 0000000000000001 R15:
    0000000000000000
    [5108912.563245] FS: 0000000000000000(0000) GS:ffff88123fc20000(0000)
    knlGS:0000000000000000
    [5108912.563248] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    [5108912.563250] CR2: 00007f692e787180 CR3: 0000000001a0b000 CR4:
    00000000000007e0
    [5108912.563252] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
    0000000000000000
    [5108912.563254] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
    0000000000000400
    [5108912.563256] Process perf (pid: 13856, threadinfo
    ffff8809ea39a000, task ffff880a2167c470)
    [5108912.563258] Stack:
    [5108912.563260] ffff880a3a6c32c0 ffff88048c7c3820 ffff8809ea39bd88
    ffff88048c7c3800
    [5108912.563265] ffff88048c7c3800 ffff8808f8541c00 ffff8808f8541c10
    ffff88091b56c000
    [5108912.563269] ffff8809ea39bdb8 ffffffff810d9bbe ffff8809ea39bdb8
    ffff880a2167c470
    [5108912.563273] Call Trace:
    [5108912.563278] [<ffffffff810d9bbe>] perf_event_release_kernel+0x77/0x91
    [5108912.563282] [<ffffffff810d9c56>] put_event+0x7e/0x86
    [5108912.563285] [<ffffffff810d9dc0>] perf_release+0x10/0x14
    [5108912.563291] [<ffffffff8112dfc0>] __fput+0xfe/0x1f6
    [5108912.563294] [<ffffffff8112e0d2>] fput+0x1a/0x1c
    [5108912.563297] [<ffffffff8112ad8d>] filp_close+0x72/0x7d
    [5108912.563303] [<ffffffff8103efbf>] put_files_struct+0x6c/0xc3
    [5108912.563306] [<ffffffff8103f057>] exit_files+0x41/0x46
    [5108912.563309] [<ffffffff81040971>] do_exit+0x292/0x3b6
    [5108912.563312] [<ffffffff81040b12>] do_group_exit+0x7d/0xa5
    [5108912.563315] [<ffffffff81040b51>] sys_exit_group+0x17/0x1b
    [5108912.563320] [<ffffffff814c2469>] system_call_fastpath+0x16/0x1b


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