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    SubjectRe: raid5 crash

    On Wed, 2004-12-22 at 23:08, Neil Brown wrote:

    > > kernel BUG at drivers/md/raid5.c:813!
    > This BUG happens when there are two outstanding read (or write)
    > requests for the same piece of storage (more accurately, two "bio"s
    > that overlap).


    > raid5 cannot currently handle this situation.
    > Most filesystems would never make requests like this.

    I don't think there's anything to stop me doing two O_DIRECT read()s
    from the same bit of a file at the same time. As far as I can see, this
    should be easily triggered by user-space.

    And if you get corruption in a filesystem such that two files share the
    same block, then this possibility arises again. That can happen due to
    corruption in an indirect block (ext2/3) or in the reiserfs tree; or
    more commonly due to a bitmap block getting corrupted, resulting in the
    same block being allocated twice.

    This is a situation we really need to handle. ext3 goes to great
    lengths to make sure that if such cases happen, the worst that results
    should be the filesystem taking itself readonly cleanly.

    It's really bad behaviour for a fault such as a bad IDE cable to be able
    to oops the entire kernel.

    > I doubt very much that this would happen with ext3.

    It certainly shouldn't do so for buffered IO if things are running fine,
    but as soon as you get corrupt data, or start using O_DIRECT, it's


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