From d0852df543e5aa7db34c1ad26d053782bcbf48f1 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Wed, 27 May 2015 08:43:45 +1000 Subject: [PATCH] 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: Shaohua Li Signed-off-by: NeilBrown --- drivers/md/raid5.c | 25 ++++++++++++++++++++++--- drivers/md/raid5.h | 3 +++ 2 files changed, 25 insertions(+), 3 deletions(-) diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index c55a68f37c72..42d0ea6c8597 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -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); - sh->bm_seq = conf->seq_flush+1; - set_bit(STRIPE_BIT_DELAY, &sh->state); + 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); diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h index 7dc0dd86074b..01cdb9f3a0c4 100644 --- a/drivers/md/raid5.h +++ b/drivers/md/raid5.h @@ -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 \