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blk-mq: fix potential io hang by wrong 'wake_batch'
In __blk_mq_tag_busy/idle(), updating 'active_queues' and calculating
'wake_batch' is not atomic:
t1: t2:
_blk_mq_tag_busy blk_mq_tag_busy
inc active_queues
// assume 1->2
inc active_queues
// 2 -> 3
blk_mq_update_wake_batch
// calculate based on 3
blk_mq_update_wake_batch
/* calculate based on 2, while active_queues is actually 3. */
Fix this problem by protecting them wih 'tags->lock', this is not a hot
path, so performance should not be concerned. And now that all writers
are inside the lock, switch 'actives_queues' from atomic to unsigned
int.
Fixes: 180dccb0db
("blk-mq: fix tag_get wait task can't be awakened")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230610023043.2559121-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
parent
0733ad8002
commit
4f1731df60
@ -401,7 +401,7 @@ static void blk_mq_debugfs_tags_show(struct seq_file *m,
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seq_printf(m, "nr_tags=%u\n", tags->nr_tags);
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seq_printf(m, "nr_reserved_tags=%u\n", tags->nr_reserved_tags);
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seq_printf(m, "active_queues=%d\n",
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atomic_read(&tags->active_queues));
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READ_ONCE(tags->active_queues));
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seq_puts(m, "\nbitmap_tags:\n");
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sbitmap_queue_show(&tags->bitmap_tags, m);
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@ -38,6 +38,7 @@ static void blk_mq_update_wake_batch(struct blk_mq_tags *tags,
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void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
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{
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unsigned int users;
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struct blk_mq_tags *tags = hctx->tags;
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if (blk_mq_is_shared_tags(hctx->flags)) {
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struct request_queue *q = hctx->queue;
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@ -51,9 +52,11 @@ void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
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set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state);
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}
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users = atomic_inc_return(&hctx->tags->active_queues);
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blk_mq_update_wake_batch(hctx->tags, users);
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spin_lock_irq(&tags->lock);
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users = tags->active_queues + 1;
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WRITE_ONCE(tags->active_queues, users);
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blk_mq_update_wake_batch(tags, users);
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spin_unlock_irq(&tags->lock);
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}
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/*
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@ -86,9 +89,11 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
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return;
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}
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users = atomic_dec_return(&tags->active_queues);
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spin_lock_irq(&tags->lock);
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users = tags->active_queues - 1;
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WRITE_ONCE(tags->active_queues, users);
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blk_mq_update_wake_batch(tags, users);
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spin_unlock_irq(&tags->lock);
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blk_mq_tag_wakeup_all(tags, false);
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}
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@ -412,8 +412,7 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
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return true;
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}
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users = atomic_read(&hctx->tags->active_queues);
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users = READ_ONCE(hctx->tags->active_queues);
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if (!users)
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return true;
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@ -739,8 +739,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
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struct blk_mq_tags {
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unsigned int nr_tags;
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unsigned int nr_reserved_tags;
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atomic_t active_queues;
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unsigned int active_queues;
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struct sbitmap_queue bitmap_tags;
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struct sbitmap_queue breserved_tags;
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