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    SubjectRe: Kernel panics on raw I/O stress test

    > Could you try again with 2.4.4pre4 plus the below patch?

    I suppose that 2.4.4-pre4 + rawio-3 patch still has SMP-unsafe
    raw i/o code and can cause the same panic I reported.

    I think the following scenario is possible if there are 3 or more CPUs.

    (1) CPU0 enter rw_raw_dev()
    (2) CPU0 execute alloc_kiovec(1, &iobuf) // drivers/char/raw.c line 309
    (3) CPU0 enter brw_kiovec(rw, 1, &iobuf,..) // drivers/char/raw.c line 362
    (4) CPU0 enter __wait_on_buffer()
    (5) CPU0 execute run_task_queue() and wait
    while buffer_locked(bh) is true. // fs/buffer.c line 152-158
    (6) CPU1 enter end_buffer_io_kiobuf() with
    iobuf allocated at (2)
    (7) CPU1 execute unlock_buffer() // fs/buffer.c line 1994
    (8) CPU0 exit __wait_on_buffer()
    (9) CPU0 exit brw_kiovec(rw, 1, &iobuf,..)
    (10) CPU0 execute free_kiovec(1, &iobuf) // drivers/char/raw.c line 388
    (11) The task on CPU2 reused the area freed
    at (10).
    (12) CPU1 enter end_kio_request() and touch
    the corrupted iobuf, then panic.

    Takanori Kawano
    Hitachi Ltd,
    Internet Systems Platform Division

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