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Subject[tip: locking/core] raid5: Use sequence counter with associated spinlock
The following commit has been merged into the locking/core branch of tip:

Commit-ID: 0a87b25ff2eb6169403c88b0d5f3c97bdaa3c930
Author: Ahmed S. Darwish <>
AuthorDate: Mon, 20 Jul 2020 17:55:25 +02:00
Committer: Peter Zijlstra <>
CommitterDate: Wed, 29 Jul 2020 16:14:27 +02:00

raid5: Use sequence counter with associated spinlock

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 <>
Signed-off-by: Peter Zijlstra (Intel) <>
Acked-by: Song Liu <>
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 ab8067f..892aefe 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;
- seqcount_init(&conf->gen_lock);
+ seqcount_spinlock_init(&conf->gen_lock, &conf->device_lock);
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index f90e070..a2c9e9e 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
 \ /
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