linux-kernel - [PATCH] block: Use WRITE_ONCE for cache->nr

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Message-Id: <20241104113745.3099644-1-zilinguan811@gmail.com>
Date: Mon,  4 Nov 2024 11:37:45 +0000
From: Zilin Guan <zilinguan811@...il.com>
To: axboe@...nel.dk
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Zilin Guan <zilinguan811@...il.com>
Subject: [PATCH] block: Use WRITE_ONCE for cache->nr_irq update

In function bio_put_percpu_cache(), cache->nr_irq is read indirectly
in line 776 using READ_ONCE(). This ensures safe access in a
multi-threaded environment.

776     if (READ_ONCE(cache->nr_irq) + cache->nr > ALLOC_CACHE_MAX)
777             goto out_free;

However, the increment operation is performed directly in line 792 without
using WRITE_ONCE(), which can lead to potential inconsistencies in a
multi-threaded context.

792     cache->nr_irq++;

To ensure consistent protection against data races, this update
should utilize WRITE_ONCE.

Signed-off-by: Zilin Guan <zilinguan811@...il.com>
---
 block/bio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index ac4d77c88932..e2648ba71bac 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -789,7 +789,7 @@ static inline void bio_put_percpu_cache(struct bio *bio)
 		bio_uninit(bio);
 		bio->bi_next = cache->free_list_irq;
 		cache->free_list_irq = bio;
-		cache->nr_irq++;
+		WRITE_ONCE(cache->nr_irq, cache->nr_irq + 1);
 	} else {
 		goto out_free;
 	}
-- 
2.34.1