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    SubjectRe: Dumb question: BKL on reboot ?
    Andrea Arcangeli wrote:
    > On Thu, Aug 21, 2003 at 10:05:20AM +0200, Hannes Reinecke wrote:
    [ .. ]
    >>Exactly what happened here. CPU#1 entered sys_reboot, got BKL and
    >>prepared to stop. It will never release BKL, leaving a nice big window
    >>for CPU#0 to deadlock.
    > if that was really the case it shouldn't deadlock, because CPU0
    > shouldn't depend on a big kernel lock to be able to re-enable the irqs,
    > and to receive the IPI. Nor any IPI handler could ever be allowed to
    > take the big kernel lock.
    > Unless you can demonstrate a dependency on the big kernel lock for CPU0
    > to re-enable the irqs eventually, I can't see how the above could
    > deadlock.

    What happened was this:

    TASK HAS CPU (0): 0x904000 (kupdated):
    -psw : 0x400100180000000 0x0000000007aa22
    -function : sync_old_buffers+58
    -prefix : 0x009c8000
    -cpu timer: 0xfffffa77 0x33465f80
    -clock cmp: 0x00b9e503 0x235324f4
    -general registers:
    0000000000000000 0x000000002e1000
    0x0000000007aa22 0x0000000004919e
    0x00000000907f28 0x0000000022b428
    0000000000000000 0000000000000000
    0x00000000224340 0000000000000000
    0x00000000970000 0x00000000233b00
    0x00000000904000 0x000000001deb60
    0x00000000907e78 0x00000000907dd8
    [ .. ]
    0 kupdate+424 [0x7af4c]
    1 arch_kernel_thread+70 [0x18d72]
    TASK HAS CPU (1): 0x3318000 (reboot):
    -psw : 0x700100180000000 0x0000007ffe0d8e
    -function : not found in System map
    -prefix : 0x009c2000
    -cpu timer: 0xfff79e2d 0x014244c0
    -clock cmp: 0x00b9e503 0x3a5d9504
    -general registers:
    0x00000000000001 0000000000000000
    0000000000000000 0000000000000000
    0x0000000001f268 0000000000000000
    0x00000000000003 0x000000000002c0
    0x000000000490f0 0x00000003318000
    0x00000000016422 0000000000000000
    0x00000000000001 0x000000001da280
    0x0000000001f268 0x0000000331bae0
    [ .. ]
    0 machine_restart_smp+62 [0x1f5f2]
    1 machine_restart+48 [0x19884]
    2 sys_reboot+306 [0x49222]
    3 sysc_noemu+16 [0x16242]

    Not sure why CPU#0 wanted to execute kupdate(), but hey ...


    Dr. Hannes Reinecke
    SuSE Linux AG S390 & zSeries
    Deutschherrnstr. 15-19 +49 911 74053 688
    90429 Nürnberg

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      Last update: 2005-03-22 13:47    [W:0.023 / U:14.432 seconds]
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