linux-kernel - [tip: locking/core] raid5: Use sequence counter with associated spinlock

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Date:   Wed, 29 Jul 2020 14:33:30 -0000
From:   "tip-bot2 for Ahmed S. Darwish" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Song Liu <song@...nel.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
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
Gitweb:        https://git.kernel.org/tip/0a87b25ff2eb6169403c88b0d5f3c97bdaa3c930
Author:        Ahmed S. Darwish <a.darwish@...utronix.de>
AuthorDate:    Mon, 20 Jul 2020 17:55:25 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
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 <a.darwish@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Song Liu <song@...nel.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-20-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 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;
 	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 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