Commit 0a87b25f authored Jul 20, 2020 by Ahmed S. Darwish Committed by Peter Zijlstra Jul 29, 2020

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@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Song Liu <song@kernel.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-20-a.darwish@linutronix.de

parent 26475371

drivers/md/raid5.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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);

drivers/md/raid5.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -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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