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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Filipe Manana <fdmanana@suse.com>,
        Naohiro Aota <naohiro.aota@wdc.com>,
        David Sterba <dsterba@suse.com>
Subject: [PATCH 5.17 193/219] btrfs: mark resumed async balance as writing
Date:   Mon, 18 Apr 2022 14:12:42 +0200
Message-Id: <20220418121212.277352250@linuxfoundation.org>
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From: Naohiro Aota <naohiro.aota@wdc.com>

commit a690e5f2db4d1dca742ce734aaff9f3112d63764 upstream.

When btrfs balance is interrupted with umount, the background balance
resumes on the next mount. There is a potential deadlock with FS freezing
here like as described in commit 26559780b953 ("btrfs: zoned: mark
relocation as writing"). Mark the process as sb_writing to avoid it.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
CC: stable@vger.kernel.org # 4.9+
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/btrfs/volumes.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4467,10 +4467,12 @@ static int balance_kthread(void *data)
 	struct btrfs_fs_info *fs_info = data;
 	int ret = 0;
 
+	sb_start_write(fs_info->sb);
 	mutex_lock(&fs_info->balance_mutex);
 	if (fs_info->balance_ctl)
 		ret = btrfs_balance(fs_info, fs_info->balance_ctl, NULL);
 	mutex_unlock(&fs_info->balance_mutex);
+	sb_end_write(fs_info->sb);
 
 	return ret;
 }