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    Subject[PATCH 3.16.y-ckt 79/94] md/raid5: fix locking in handle_stripe_clean_event()
    Date
    3.16.7-ckt20 -stable review patch.  If anyone has any objections, please let me know.

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

    From: Roman Gushchin <klamm@yandex-team.ru>

    commit b8a9d66d043ffac116100775a469f05f5158c16f upstream.

    After commit 566c09c53455 ("raid5: relieve lock contention in get_active_stripe()")
    __find_stripe() is called under conf->hash_locks + hash.
    But handle_stripe_clean_event() calls remove_hash() under
    conf->device_lock.

    Under some cirscumstances the hash chain can be circuited,
    and we get an infinite loop with disabled interrupts and locked hash
    lock in __find_stripe(). This leads to hard lockup on multiple CPUs
    and following system crash.

    I was able to reproduce this behavior on raid6 over 6 ssd disks.
    The devices_handle_discard_safely option should be set to enable trim
    support. The following script was used:

    for i in `seq 1 32`; do
    dd if=/dev/zero of=large$i bs=10M count=100 &
    done

    Signed-off-by: Roman Gushchin <klamm@yandex-team.ru>
    Fixes: 566c09c53455 ("raid5: relieve lock contention in get_active_stripe()")
    Signed-off-by: NeilBrown <neilb@suse.com>
    Cc: Shaohua Li <shli@kernel.org>
    [ luis: backported to 3.16: used Roman's backport to 3.14 ]
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    drivers/md/raid5.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
    index 6d7d2f3059a7..f90752ce95dc 100644
    --- a/drivers/md/raid5.c
    +++ b/drivers/md/raid5.c
    @@ -3069,6 +3069,8 @@ static void handle_stripe_clean_event(struct r5conf *conf,
    }
    if (!discard_pending &&
    test_bit(R5_Discard, &sh->dev[sh->pd_idx].flags)) {
    + int hash = sh->hash_lock_index;
    +
    clear_bit(R5_Discard, &sh->dev[sh->pd_idx].flags);
    clear_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags);
    if (sh->qd_idx >= 0) {
    @@ -3082,9 +3084,9 @@ static void handle_stripe_clean_event(struct r5conf *conf,
    * no updated data, so remove it from hash list and the stripe
    * will be reinitialized
    */
    - spin_lock_irq(&conf->device_lock);
    + spin_lock_irq(conf->hash_locks + hash);
    remove_hash(sh);
    - spin_unlock_irq(&conf->device_lock);
    + spin_unlock_irq(conf->hash_locks + hash);
    if (test_bit(STRIPE_SYNC_REQUESTED, &sh->state))
    set_bit(STRIPE_HANDLE, &sh->state);


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