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    SubjectRe: [PATCH] was: [RFC] removal of sync in panic
    Andrew Morton wrote:
    > I agree with the patch in principle, but I'd be interested in what
    > observed problem motivated it?

    see the first posting.

    I have seen panic failing two times lately on an SMP system. The box
    panic'ed but was running happily on the other cpus. The culprit of this
    failure is the fact, that these panics have been caused by a block device
    or a filesystem (e.g. using errors=panic). In these cases the likelihood
    of a failure/hang of sys_sync() is high. This is exactly what happened in
    both cases I have seen. Meanwhile the other cpus are happily continuing
    destroying data as the kernel has a severe problem but its not aware of
    that as smp_send_stop happens after sys_sync.

    I can imagine several changes but I am not sure if this is a problem which
    must be fixed and which fix is the best.
    Here are my alternatives:

    1. remove sys_sync completely: syslogd and klogd use fsync. No need to help
    them. Furthermore we have a severe problem which is worth a panic, so we
    better dont do any I/O.
    2. move smp_send_stop before sys_sync. This at least prevents other cpus of
    doing harm if sys_sync hangs. Here I am not sure if this is really working.
    3. Add an
    if (doing_io())
    printk(KERN_EMERG "In I/O routine - not syncing\n");
    check like in_interrupt check. Unfortunately I have no clue how this can be
    achieved and it looks quite ugly.
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