Commit d0852df5 authored by NeilBrown's avatar NeilBrown
Browse files

md/raid5: close race between STRIPE_BIT_DELAY and batching. 



When we add a write to a stripe we need to make sure the bitmap
bit is set.  While doing that the stripe is not locked so it could
be added to a batch after which further changes to STRIPE_BIT_DELAY
and ->bm_seq are ineffective.

So we need to hold off adding to a stripe until bitmap_startwrite has
completed at least once, and we need to avoid further changes to
STRIPE_BIT_DELAY once the stripe has been added to a batch.

If a bitmap_startwrite() completes after the stripe was added to a
batch, it will not have set the bit, only incremented a counter, so no
extra delay of the stripe is needed.

Reported-by: default avatarShaohua Li <shli@kernel.org>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent 2b6b2457

drivers/md/raid5.c

+22 −3
Original line number Diff line number Diff line
@@ -749,6 +749,7 @@ static void unlock_two_stripes(struct stripe_head *sh1, struct stripe_head *sh2) 
static bool stripe_can_batch(struct stripe_head *sh)

{

	return test_bit(STRIPE_BATCH_READY, &sh->state) &&

		!test_bit(STRIPE_BITMAP_PENDING, &sh->state) &&

		is_full_stripe_write(sh);

}
@@ -2996,14 +2997,32 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, 
	pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",

		(unsigned long long)(*bip)->bi_iter.bi_sector,

		(unsigned long long)sh->sector, dd_idx);

	spin_unlock_irq(&sh->stripe_lock);



	if (conf->mddev->bitmap && firstwrite) {

		/* Cannot hold spinlock over bitmap_startwrite,

		 * but must ensure this isn't added to a batch until

		 * we have added to the bitmap and set bm_seq.

		 * So set STRIPE_BITMAP_PENDING to prevent

		 * batching.

		 * If multiple add_stripe_bio() calls race here they

		 * much all set STRIPE_BITMAP_PENDING.  So only the first one

		 * to complete "bitmap_startwrite" gets to set

		 * STRIPE_BIT_DELAY.  This is important as once a stripe

		 * is added to a batch, STRIPE_BIT_DELAY cannot be changed

		 * any more.

		 */

		set_bit(STRIPE_BITMAP_PENDING, &sh->state);

		spin_unlock_irq(&sh->stripe_lock);

		bitmap_startwrite(conf->mddev->bitmap, sh->sector,

				  STRIPE_SECTORS, 0);

		spin_lock_irq(&sh->stripe_lock);

		clear_bit(STRIPE_BITMAP_PENDING, &sh->state);

		if (!sh->batch_head) {

			sh->bm_seq = conf->seq_flush+1;

			set_bit(STRIPE_BIT_DELAY, &sh->state);

		}

	}

	spin_unlock_irq(&sh->stripe_lock);



	if (stripe_can_batch(sh))

		stripe_add_to_batch_list(conf, sh);

drivers/md/raid5.h

+3 −0
Original line number Diff line number Diff line
@@ -337,6 +337,9 @@ enum { 
	STRIPE_ON_RELEASE_LIST,

	STRIPE_BATCH_READY,

	STRIPE_BATCH_ERR,

	STRIPE_BITMAP_PENDING,	/* Being added to bitmap, don't add

				 * to batch yet.

				 */

};



#define STRIPE_EXPAND_SYNC_FLAG \

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