On Sun, Nov 24, 2024 at 07:38:45AM -0500, Sasha Levin wrote:
From: Qu Wenruo wqu@suse.com
[ Upstream commit a4ef54dbb576032ba31a646a5ffc8a26a83cb92c ]
For btrfs with sector size < page size (e.g. 4K sector size, 64K page size), and enable the sector perfect compression support, then the following dirty range can lead to problems:
0 32K 64K 96K 128K | |///////||//////| |/| 124K
In above case, if we start writeback for that inode, the last dirty range [124K, 128K) will not be submitted and cause reserved space leakage:
Start writeback for page 0 We find the range [32K, 96K) is suitable for compression, and queue it into a workqueue to do the delayed compression and submission.
Compression happens for range [32K, 96K) Function extent_range_clear_dirty_for_io() is called, however it is only doing full page handling, not considering any the extra bitmaps for subpage cases.
That function will clear page dirty for both page 0 and page 64K.
Writeback for the inode is done Because page 64K has its dirty flag cleared, it will not be considered as a writeback target.
This means the range [124K, 128K) will not be submitted, and reserved space for it will be leaked.
Fix this problem by using the subpage helper to clear the dirty flag.
Signed-off-by: Qu Wenruo wqu@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org
Please drop this patch from stable, it's preparatory work and has otherwise no effect.