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From: Mikhail Ukhin <mish.uxin2012@yandex.ru>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: Mikhail Ukhin <mish.uxin2012@yandex.ru>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	linux-ext4@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Michail Ivanov <iwanov-23@bk.ru>,
	Pavel Koshutin <koshutin.pavel@yandex.ru>,
	Artem Sadovnikov <ancowi69@gmail.com>
Subject: [PATCH] ext4: fix semaphore unlocking order
Date: Thu, 28 Mar 2024 17:33:01 +0300
Message-Id: <20240328143301.6432-1-mish.uxin2012@yandex.ru>
Precedence: bulk
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Fuzzing reports a possible deadlock in jbd2_log_wait_commit.

The problem occurs in ext4_ind_migrate due to an incorrect order of
unlocking of the journal and write semaphores - the order of unlocking
must be the reverse of the order of locking.

Found by Linux Verification Center (linuxtesting.org) with syzkaller.

Signed-off-by: Artem Sadovnikov <ancowi69@gmail.com>
---
 fs/ext4/migrate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c
index d98ac2af8199..a5e1492bbaaa 100644
--- a/fs/ext4/migrate.c
+++ b/fs/ext4/migrate.c
@@ -663,8 +663,8 @@ int ext4_ind_migrate(struct inode *inode)
 	if (unlikely(ret2 && !ret))
 		ret = ret2;
 errout:
-	ext4_journal_stop(handle);
 	up_write(&EXT4_I(inode)->i_data_sem);
+	ext4_journal_stop(handle);
 out_unlock:
 	ext4_writepages_up_write(inode->i_sb, alloc_ctx);
 	return ret;
-- 
2.25.1