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    Fix race with shared tag queue maps · f3da54ba
    Jens Axboe 提交于
    There's a race condition in blk_queue_end_tag() for shared tag maps,
    users include stex (promise supertrak thingy) and qla2xxx.  The former
    at least has reported bugs in this area, not sure why we haven't seen
    any for the latter.  It could be because the window is narrow and that
    other conditions in the qla2xxx code hide this.  It's a real bug,
    though, as the stex smp users can attest.
    
    We need to ensure two things - the tag bit clearing needs to happen
    AFTER we cleared the tag pointer, as the tag bit clearing/setting is
    what protects this map.  Secondly, we need to ensure that the visibility
    of the tag pointer and tag bit clear are ordered properly.
    
    [ I removed the SMP barriers - "test_and_clear_bit()" already implies
      all the required barriers.  -- Linus ]
    
    Also see http://bugzilla.kernel.org/show_bug.cgi?id=7842Signed-off-by: NJens Axboe <jens.axboe@oracle.com>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    f3da54ba
ll_rw_blk.c 105.3 KB