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    SubjectRe: 2.6.30-rc2 hangs in get_measured_perf on tigerton
    Date
    On Wed, 15 Apr 2009 03:31:23 pm Zhang, Yanmin wrote:
    > My machine hanged with kernel 2.6.30-rc2 when script read
    > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor.
    >
    > opps happens in get_measured_perf:
    >
    > cur.aperf.whole = readin.aperf.whole -
    > per_cpu(drv_data, cpu)->saved_aperf;
    >
    > Because per_cpu(drv_data, cpu)=NULL.
    >
    > So function get_measured_perf should check if (per_cpu(drv_data, cpu)==NULL)
    > and return 0 if it's NULL.
    >
    > Other functions have such checking.

    Possibly true, but I can't see that get_measured_perf() ever did.

    Unless there's something subtle with preemption no longer being disabled
    inside that function...

    Cc'd the experts.

    Thanks,
    Rusty.

    >
    > yanmin
    >
    >
    >
    > --------------sys log------------------
    >
    > BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
    > IP: [<ffffffff8021af75>] get_measured_perf+0x4a/0xf9
    > PGD a7dd88067 PUD a7ccf5067 PMD 0
    > Oops: 0000 [#1] SMP
    > last sysfs file: /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
    > CPU 0
    > Modules linked in: video output
    > Pid: 2091, comm: kondemand/0 Not tainted 2.6.30-rc2 #1 MP Server
    > RIP: 0010:[<ffffffff8021af75>] [<ffffffff8021af75>] get_measured_perf+0x4a/0xf9
    > RSP: 0018:ffff880a7d56de20 EFLAGS: 00010246
    > RAX: 0000000000000000 RBX: 00000046241a42b6 RCX: ffff88004d219000
    > RDX: 000000000000b660 RSI: 0000000000000020 RDI: 0000000000000001
    > RBP: ffff880a7f052000 R08: 00000046241a42b6 R09: ffffffff807639f0
    > R10: 00000000ffffffea R11: ffffffff802207f4 R12: ffff880a7f052000
    > R13: ffff88004d20e460 R14: 0000000000ddd5a6 R15: 0000000000000001
    > FS: 0000000000000000(0000) GS:ffff88004d200000(0000) knlGS:0000000000000000
    > CS: 0010 DS: 0018 ES: 0018 CR0: 000000008005003b
    > CR2: 0000000000000020 CR3: 0000000a7f1bf000 CR4: 00000000000006e0
    > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
    > Process kondemand/0 (pid: 2091, threadinfo ffff880a7d56c000, task ffff880a7d4d18c0)
    > Stack:
    > ffff880a7f052078 ffffffff803efd54 00000046241a42b6 000000462ffa9e95
    > 0000000000000001 0000000000000001 00000000ffffffea ffffffff8064f41a
    > 0000000000000012 0000000000000012 ffff880a7f052000 ffffffff80650547
    > Call Trace:
    > [<ffffffff803efd54>] ? kobject_get+0x12/0x17
    > [<ffffffff8064f41a>] ? __cpufreq_driver_getavg+0x42/0x57
    > [<ffffffff80650547>] ? do_dbs_timer+0x147/0x272
    > [<ffffffff80650400>] ? do_dbs_timer+0x0/0x272
    > [<ffffffff802474ca>] ? worker_thread+0x15b/0x1f5
    > [<ffffffff8024a02c>] ? autoremove_wake_function+0x0/0x2e
    > [<ffffffff8024736f>] ? worker_thread+0x0/0x1f5
    > [<ffffffff80249f0d>] ? kthread+0x54/0x83
    > [<ffffffff8020c87a>] ? child_rip+0xa/0x20
    > [<ffffffff80249eb9>] ? kthread+0x0/0x83
    > [<ffffffff8020c870>] ? child_rip+0x0/0x20
    > Code: 99 a6 03 00 31 c9 85 c0 0f 85 c3 00 00 00 89 df 4c 8b 44 24 10 48 c7 c2 60 b6 00 00 48 8b 0c fd e0 30 a5 80 4c 89 c3 48 8b 04 0a <48> 2b 58 20 48 8b 44 24 18 48 89 1c 24 48 8b 34 0a 48 2b 46 28
    > RIP [<ffffffff8021af75>] get_measured_perf+0x4a/0xf9
    > RSP <ffff880a7d56de20>
    > CR2: 0000000000000020
    > ---[ end trace 2b8fac9a49e19ad4 ]---
    >
    >
    --
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