forked from Minki/linux
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 <shli@kernel.org> Signed-off-by: NeilBrown <neilb@suse.de>
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2b6b245742
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@ -749,6 +749,7 @@ static void unlock_two_stripes(struct stripe_head *sh1, struct stripe_head *sh2)
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static bool stripe_can_batch(struct stripe_head *sh)
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{
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return test_bit(STRIPE_BATCH_READY, &sh->state) &&
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!test_bit(STRIPE_BITMAP_PENDING, &sh->state) &&
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is_full_stripe_write(sh);
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}
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@ -2996,14 +2997,32 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx,
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pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
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(unsigned long long)(*bip)->bi_iter.bi_sector,
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(unsigned long long)sh->sector, dd_idx);
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spin_unlock_irq(&sh->stripe_lock);
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if (conf->mddev->bitmap && firstwrite) {
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/* Cannot hold spinlock over bitmap_startwrite,
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* but must ensure this isn't added to a batch until
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* we have added to the bitmap and set bm_seq.
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* So set STRIPE_BITMAP_PENDING to prevent
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* batching.
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* If multiple add_stripe_bio() calls race here they
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* much all set STRIPE_BITMAP_PENDING. So only the first one
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* to complete "bitmap_startwrite" gets to set
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* STRIPE_BIT_DELAY. This is important as once a stripe
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* is added to a batch, STRIPE_BIT_DELAY cannot be changed
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* any more.
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*/
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set_bit(STRIPE_BITMAP_PENDING, &sh->state);
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spin_unlock_irq(&sh->stripe_lock);
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bitmap_startwrite(conf->mddev->bitmap, sh->sector,
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STRIPE_SECTORS, 0);
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sh->bm_seq = conf->seq_flush+1;
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set_bit(STRIPE_BIT_DELAY, &sh->state);
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spin_lock_irq(&sh->stripe_lock);
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clear_bit(STRIPE_BITMAP_PENDING, &sh->state);
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if (!sh->batch_head) {
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sh->bm_seq = conf->seq_flush+1;
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set_bit(STRIPE_BIT_DELAY, &sh->state);
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}
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}
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spin_unlock_irq(&sh->stripe_lock);
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if (stripe_can_batch(sh))
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stripe_add_to_batch_list(conf, sh);
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@ -337,6 +337,9 @@ enum {
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STRIPE_ON_RELEASE_LIST,
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STRIPE_BATCH_READY,
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STRIPE_BATCH_ERR,
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STRIPE_BITMAP_PENDING, /* Being added to bitmap, don't add
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* to batch yet.
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*/
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};
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#define STRIPE_EXPAND_SYNC_FLAG \
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