From 04a6a536bc3fd1436fc78c546c6b3ecdccbfaf6d Mon Sep 17 00:00:00 2001 From: Satya Tangirala Date: Thu, 24 Dec 2020 04:49:54 +0000 Subject: [PATCH] fs: Fix freeze_bdev()/thaw_bdev() accounting of bd_fsfreeze_sb freeze/thaw_bdev() currently use bdev->bd_fsfreeze_count to infer whether or not bdev->bd_fsfreeze_sb is valid (it's valid iff bd_fsfreeze_count is non-zero). thaw_bdev() doesn't nullify bd_fsfreeze_sb. But this means a freeze_bdev() call followed by a thaw_bdev() call can leave bd_fsfreeze_sb with a non-null value, while bd_fsfreeze_count is zero. If freeze_bdev() is called again, and this time get_active_super() returns NULL (e.g. because the FS is unmounted), we'll end up with bd_fsfreeze_count > 0, but bd_fsfreeze_sb is *untouched* - it stays the same (now garbage) value. A subsequent thaw_bdev() will decide that the bd_fsfreeze_sb value is legitimate (since bd_fsfreeze_count > 0), and attempt to use it. Fix this by always setting bd_fsfreeze_sb to NULL when bd_fsfreeze_count is successfully decremented to 0 in thaw_sb(). Alternatively, we could set bd_fsfreeze_sb to whatever get_active_super() returns in freeze_bdev() whenever bd_fsfreeze_count is successfully incremented to 1 from 0 (which can be achieved cleanly by moving the line currently setting bd_fsfreeze_sb to immediately after the "sync:" label, but it might be a little too subtle/easily overlooked in future). This fixes the currently panicking xfstests generic/085. Fixes: 040f04bd2e82 ("fs: simplify freeze_bdev/thaw_bdev") Signed-off-by: Satya Tangirala Reviewed-by: Christoph Hellwig Reviewed-by: Darrick J. Wong Signed-off-by: Jens Axboe --- fs/block_dev.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/block_dev.c b/fs/block_dev.c index 3e5b02f6606c..e454c5a81043 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -605,6 +605,8 @@ int thaw_bdev(struct block_device *bdev) error = thaw_super(sb); if (error) bdev->bd_fsfreeze_count++; + else + bdev->bd_fsfreeze_sb = NULL; out: mutex_unlock(&bdev->bd_fsfreeze_mutex); return error;