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    Subject2.6.17-rc5-mm3 - crash in cfq_queue_empty() after iosched change
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    I've been hitting this about once every two weeks for a while now, probably
    back to a 2.6.16-rc or so. It always bites at the same time while my laptop
    was at a point very late in bootup. I finally caught one when I had pen, paper,
    *and* time to chase it a bit rather than reboot. Sorry for the very partial
    traceback, it's not a good CTS day and I didn't have a digital camera handy.

    BUG: Unable to handle kernel NULL pointer dereference at 0x0000005c
    EIP at cfq_queue_empty+0x9/0x15
    call trace:
    elv_queue_empty+0x20/0x22
    ide_do_request+0xa4/0x788
    ide_intr+0x1ec/0x236
    handle_IRQ_eent+0x27/0x52
    handle_level_IRQ+0xb6
    do_IRQ+0x5d/0x78
    common_interrupt+0x1a/0x20

    In my .config:

    CONFIG_IOSCHED_NOOP=y
    CONFIG_IOSCHED_AS=y
    CONFIG_IOSCHED_DEADLINE=y
    CONFIG_IOSCHED_CFQ=y
    CONFIG_DEFAULT_IOSCHED="anticipatory"

    This happened very soon (within a few milliseconds or two) after my /etc/rc.local did:

    echo cfq >| /sys/block/hda/queue/scheduler

    (The next executable statement in /etc/rc.local is this:
    echo noop >| /sys/block/hdb/queue/scheduler and 'last sysfs file' still
    pointed at /dev/hda).

    It *looks* like the problem is in elevator_switch() in block/elevator.c:

    while (q->rq.elvpriv) {
    blk_remove_plug(q);
    q->request_fn(q);
    spin_unlock_irq(q->queue_lock);
    msleep(10);
    spin_lock_irq(q->queue_lock);
    elv_drain_elevator(q);
    }

    this--> spin_unlock_irq(q->queue_lock);

    /*
    * unregister old elevator data
    */
    elv_unregister_queue(q);
    old_elevator = q->elevator;

    /*
    * attach and start new elevator
    */
    if (elevator_attach(q, e))
    goto fail;

    should be down here someplace, after elevator_attach(), I suspect?
    Looks like the disk popped an IRQ after we had installed the iosched_cfq.ops[]
    but q->elevator->elevator_data hadn't been initialized yet...

    (I'd attach a patch, except I'm not positive I have the diagnosis right?)

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      Last update: 2006-06-05 16:45    [W:0.108 / U:0.080 seconds]
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