releases/6.3.13/blk-mq-fix-potential-io-hang-by-wrong-wake_batch.patch

From d74e29b02e06af5636acb504e0771b64f38b2a4d Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Sat, 10 Jun 2023 10:30:43 +0800
Subject: blk-mq: fix potential io hang by wrong 'wake_batch'

From: Yu Kuai <yukuai3@huawei.com>

[ Upstream commit 4f1731df60f9033669f024d06ae26a6301260b55 ]

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: 180dccb0dba4 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 block/blk-mq-debugfs.c |  2 +-
 block/blk-mq-tag.c     | 15 ++++++++++-----
 block/blk-mq.h         |  3 +--
 include/linux/blk-mq.h |  3 +--
 4 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index b01818f8e216e..c152276736832 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -427,7 +427,7 @@ static void blk_mq_debugfs_tags_show(struct seq_file *m,
 	seq_printf(m, "nr_tags=%u\n", tags->nr_tags);
 	seq_printf(m, "nr_reserved_tags=%u\n", tags->nr_reserved_tags);
 	seq_printf(m, "active_queues=%d\n",
-		   atomic_read(&tags->active_queues));
+		   READ_ONCE(tags->active_queues));
 
 	seq_puts(m, "\nbitmap_tags:\n");
 	sbitmap_queue_show(&tags->bitmap_tags, m);
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index a80d7c62bdfe6..100889c276c3f 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -40,6 +40,7 @@ static void blk_mq_update_wake_batch(struct blk_mq_tags *tags,
 void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
 {
 	unsigned int users;
+	struct blk_mq_tags *tags = hctx->tags;
 
 	/*
 	 * calling test_bit() prior to test_and_set_bit() is intentional,
@@ -57,9 +58,11 @@ void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
 			return;
 	}
 
-	users = atomic_inc_return(&hctx->tags->active_queues);
-
-	blk_mq_update_wake_batch(hctx->tags, users);
+	spin_lock_irq(&tags->lock);
+	users = tags->active_queues + 1;
+	WRITE_ONCE(tags->active_queues, users);
+	blk_mq_update_wake_batch(tags, users);
+	spin_unlock_irq(&tags->lock);
 }
 
 /*
@@ -92,9 +95,11 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 			return;
 	}
 
-	users = atomic_dec_return(&tags->active_queues);
-
+	spin_lock_irq(&tags->lock);
+	users = tags->active_queues - 1;
+	WRITE_ONCE(tags->active_queues, users);
 	blk_mq_update_wake_batch(tags, users);
+	spin_unlock_irq(&tags->lock);
 
 	blk_mq_tag_wakeup_all(tags, false);
 }
diff --git a/block/blk-mq.h b/block/blk-mq.h
index a7482d2cc82e7..4542308c8e62f 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -362,8 +362,7 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
 			return true;
 	}
 
-	users = atomic_read(&hctx->tags->active_queues);
-
+	users = READ_ONCE(hctx->tags->active_queues);
 	if (!users)
 		return true;
 
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index de0b0c3e7395a..4110d6e99b2b9 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -748,8 +748,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
 struct blk_mq_tags {
 	unsigned int nr_tags;
 	unsigned int nr_reserved_tags;
-
-	atomic_t active_queues;
+	unsigned int active_queues;
 
 	struct sbitmap_queue bitmap_tags;
 	struct sbitmap_queue breserved_tags;
-- 
2.39.2