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    SubjectRe: [BUG] The kernel thread for md RAID1 could cause a md RAID1 array deadlock
    Hi,

    Thank you for the patch.
    I have applied the patch to 2.6.23.14 and it works well.

    - In case of 2.6.23.14, the problem is reproduced.
    - In case of 2.6.23.14 with this patch, raid1 works well so far.
    The fault injection script continues to run, and it doesn't deadlock.
    I will keep it running for a while.

    Also, md raid10 seems to have the same problem.
    I will test raid10 applying this patch as well.


    Neil Brown wrote:
    > On Tuesday January 15, k-tanaka@ce.jp.nec.com wrote:
    >> This message describes the details about md-RAID1 issue found by
    >> testing the md RAID1 using the SCSI fault injection framework.
    >>
    >> Abstract:
    >> Both the error handler for md RAID1 and write access request to the md RAID1
    >> use raid1d kernel thread. The nr_pending flag could cause a race condition
    >> in raid1d, results in a raid1d deadlock.
    >
    > Thanks for finding and reporting this.
    >
    > I believe the following patch should fix the deadlock.
    >
    > If you are able to repeat your test and confirm this I would
    > appreciate it.
    >
    > Thanks,
    > NeilBrown
    >
    >
    >
    > Fix deadlock in md/raid1 when handling a read error.
    >
    > When handling a read error, we freeze the array to stop any other
    > IO while attempting to over-write with correct data.
    >
    > This is done in the raid1d thread and must wait for all submitted IO
    > to complete (except for requests that failed and are sitting in the
    > retry queue - these are counted in ->nr_queue and will stay there during
    > a freeze).
    >
    > However write requests need attention from raid1d as bitmap updates
    > might be required. This can cause a deadlock as raid1 is waiting for
    > requests to finish that themselves need attention from raid1d.
    >
    > So we create a new function 'flush_pending_writes' to give that attention,
    > and call it in freeze_array to be sure that we aren't waiting on raid1d.
    >
    > Thanks to "K.Tanaka" <k-tanaka@ce.jp.nec.com> for finding and reporting
    > this problem.
    >
    > Cc: "K.Tanaka" <k-tanaka@ce.jp.nec.com>
    > Signed-off-by: Neil Brown <neilb@suse.de>
    >
    --
    ---------------------------------------------------------
    Kenichi TANAKA | Open Source Software Platform Development Division
    | Computers Software Operations Unit, NEC Corporation
    | k-tanaka@ce.jp.nec.com


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