linux-kernel - [PATCH] vfs: fix up the assert in i_readcount

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Message-Id: <20230811194814.1612336-1-mjguzik@gmail.com>
Date:   Fri, 11 Aug 2023 21:48:14 +0200
From:   Mateusz Guzik <mjguzik@...il.com>
To:     brauner@...nel.org
Cc:     viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
        Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH] vfs: fix up the assert in i_readcount_dec

Drops a race where 2 threads could spot a positive value and both
proceed to dec to -1, without reporting anything.

Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
---
 include/linux/fs.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 562f2623c9c9..21c8f8ae014d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2613,8 +2613,7 @@ static inline bool inode_is_open_for_write(const struct inode *inode)
 #if defined(CONFIG_IMA) || defined(CONFIG_FILE_LOCKING)
 static inline void i_readcount_dec(struct inode *inode)
 {
-	BUG_ON(!atomic_read(&inode->i_readcount));
-	atomic_dec(&inode->i_readcount);
+	BUG_ON(atomic_dec_return(&inode->i_readcount) < 0);
 }
 static inline void i_readcount_inc(struct inode *inode)
 {
-- 
2.39.2