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    Subject[PATCH 4.4 07/41] md/raid5: preserve STRIPE_ON_UNPLUG_LIST in break_stripe_batch_list
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Dennis Yang <dennisyang@qnap.com>

    commit 184a09eb9a2fe425e49c9538f1604b05ed33cfef upstream.

    In release_stripe_plug(), if a stripe_head has its STRIPE_ON_UNPLUG_LIST
    set, it indicates that this stripe_head is already in the raid5_plug_cb
    list and release_stripe() would be called instead to drop a reference
    count. Otherwise, the STRIPE_ON_UNPLUG_LIST bit would be set for this
    stripe_head and it will get queued into the raid5_plug_cb list.

    Since break_stripe_batch_list() did not preserve STRIPE_ON_UNPLUG_LIST,
    A stripe could be re-added to plug list while it is still on that list
    in the following situation. If stripe_head A is added to another
    stripe_head B's batch list, in this case A will have its
    batch_head != NULL and be added into the plug list. After that,
    stripe_head B gets handled and called break_stripe_batch_list() to
    reset all the batched stripe_head(including A which is still on
    the plug list)'s state and reset their batch_head to NULL.
    Before the plug list gets processed, if there is another write request
    comes in and get stripe_head A, A will have its batch_head == NULL
    (cleared by calling break_stripe_batch_list() on B) and be added to
    plug list once again.

    Signed-off-by: Dennis Yang <dennisyang@qnap.com>
    Signed-off-by: Shaohua Li <shli@fb.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/md/raid5.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/drivers/md/raid5.c
    +++ b/drivers/md/raid5.c
    @@ -4264,7 +4264,8 @@ static void break_stripe_batch_list(stru

    set_mask_bits(&sh->state, ~(STRIPE_EXPAND_SYNC_FLAGS |
    (1 << STRIPE_PREREAD_ACTIVE) |
    - (1 << STRIPE_DEGRADED)),
    + (1 << STRIPE_DEGRADED) |
    + (1 << STRIPE_ON_UNPLUG_LIST)),
    head_sh->state & (1 << STRIPE_INSYNC));

    sh->check_state = head_sh->check_state;

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