From: Qu Wenruo wqu@suse.com
[ Upstream commit bcd77455d590eaa0422a5e84ae852007cfce574a ]
[BUG] With current btrfs subpage rw support, the following script can lead to fs hang:
$ mkfs.btrfs -f -s 4k $dev $ mount $dev -o nospace_cache $mnt $ fsstress -w -n 100 -p 1 -s 1608140256 -v -d $mnt
The fs will hang at btrfs_start_ordered_extent().
[CAUSE] In above test case, btrfs_invalidate() will be called with the following parameters:
offset = 0 length = 53248 page dirty = 1 subpage dirty bitmap = 0x2000
Since @offset is 0, btrfs_invalidate() will try to invalidate the full page, and finally call clear_page_extent_mapped() which will detach subpage structure from the page.
And since the page no longer has subpage structure, the subpage dirty bitmap will be cleared, preventing the dirty range from being written back, thus no way to wake up the ordered extent.
[FIX] Just follow other filesystems, only to invalidate the page if the range covers the full page.
There are cases like truncate_setsize() which can call btrfs_invalidatepage() with offset == 0 and length != 0 for the last page of an inode.
Although the old code will still try to invalidate the full page, we are still safe to just wait for ordered extent to finish. So it shouldn't cause extra problems.
Tested-by: Ritesh Harjani riteshh@linux.ibm.com # [ppc64] Tested-by: Anand Jain anand.jain@oracle.com # [aarch64] Signed-off-by: Qu Wenruo wqu@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/inode.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index d29451b839fb..454573a61132 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -8386,7 +8386,19 @@ static void btrfs_invalidatepage(struct page *page, unsigned int offset, */ wait_on_page_writeback(page);
- if (offset) { + /* + * For subpage case, we have call sites like + * btrfs_punch_hole_lock_range() which passes range not aligned to + * sectorsize. + * If the range doesn't cover the full page, we don't need to and + * shouldn't clear page extent mapped, as page->private can still + * record subpage dirty bits for other part of the range. + * + * For cases that can invalidate the full even the range doesn't + * cover the full page, like invalidating the last page, we're + * still safe to wait for ordered extent to finish. + */ + if (!(offset == 0 && length == PAGE_SIZE)) { btrfs_releasepage(page, GFP_NOFS); return; }