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    Subject[PATCH v4 19/24] raid5: Use sequence counter with associated spinlock
    Date
    A sequence counter write side critical section must be protected by some
    form of locking to serialize writers. A plain seqcount_t does not
    contain the information of which lock must be held when entering a write
    side critical section.

    Use the new seqcount_spinlock_t data type, which allows to associate a
    spinlock with the sequence counter. This enables lockdep to verify that
    the spinlock used for writer serialization is held when the write side
    critical section is entered.

    If lockdep is disabled this lock association is compiled out and has
    neither storage size nor runtime overhead.

    Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
    ---
    drivers/md/raid5.c | 2 +-
    drivers/md/raid5.h | 2 +-
    2 files changed, 2 insertions(+), 2 deletions(-)

    diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
    index ab8067f9ce8c..892aefe88fa7 100644
    --- a/drivers/md/raid5.c
    +++ b/drivers/md/raid5.c
    @@ -6935,7 +6935,7 @@ static struct r5conf *setup_conf(struct mddev *mddev)
    } else
    goto abort;
    spin_lock_init(&conf->device_lock);
    - seqcount_init(&conf->gen_lock);
    + seqcount_spinlock_init(&conf->gen_lock, &conf->device_lock);
    mutex_init(&conf->cache_size_mutex);
    init_waitqueue_head(&conf->wait_for_quiescent);
    init_waitqueue_head(&conf->wait_for_stripe);
    diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
    index f90e0704bed9..a2c9e9e9f5ac 100644
    --- a/drivers/md/raid5.h
    +++ b/drivers/md/raid5.h
    @@ -589,7 +589,7 @@ struct r5conf {
    int prev_chunk_sectors;
    int prev_algo;
    short generation; /* increments with every reshape */
    - seqcount_t gen_lock; /* lock against generation changes */
    + seqcount_spinlock_t gen_lock; /* lock against generation changes */
    unsigned long reshape_checkpoint; /* Time we last updated
    * metadata */
    long long min_offset_diff; /* minimum difference between
    --
    2.20.1
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