btrfs: don't clear uptodate on write errors

We have been consistently seeing hangs with generic/648 in our subpage
GitHub CI setup.  This is a classic deadlock, we are calling
btrfs_read_folio() on a folio, which requires holding the folio lock on
the folio, and then finding a ordered extent that overlaps that range
and calling btrfs_start_ordered_extent(), which then tries to write out
the dirty page, which requires taking the folio lock and then we
deadlock.

The hang happens because we're writing to range [1271750656, 1271767040),
page index [77621, 77622], and page 77621 is !Uptodate.  It is also Dirty,
so we call btrfs_read_folio() for 77621 and which does
btrfs_lock_and_flush_ordered_range() for that range, and we find an ordered
extent which is [1271644160, 1271746560), page index [77615, 77621].
The page indexes overlap, but the actual bytes don't overlap.  We're
holding the page lock for 77621, then call
btrfs_lock_and_flush_ordered_range() which tries to flush the dirty
page, and tries to lock 77621 again and then we deadlock.

The byte ranges do not overlap, but with subpage support if we clear
uptodate on any portion of the page we mark the entire thing as not
uptodate.

We have been clearing page uptodate on write errors, but no other file
system does this, and is in fact incorrect.  This doesn't hurt us in the
!subpage case because we can't end up with overlapped ranges that don't
also overlap on the page.

Fix this by not clearing uptodate when we have a write error.  The only
thing we should be doing in this case is setting the mapping error and
carrying on.  This makes it so we would no longer call
btrfs_read_folio() on the page as it's uptodate and eliminates the
deadlock.

With this patch we're now able to make it through a full fstests run on
our subpage blocksize VMs.

Note for stable backports: this probably goes beyond 6.1 but the code
has been cleaned up and clearing the uptodate bit must be verified on
each version independently.

CC: stable@vger.kernel.org # 6.1+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 1 insertions, 8 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index ac3fca5a5e41..6954ae763b86 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -484,10 +484,8 @@ static void end_bio_extent_writepage(struct btrfs_bio *bbio)
 				   bvec->bv_offset, bvec->bv_len);
 
 		btrfs_finish_ordered_extent(bbio->ordered, page, start, len, !error);
-		if (error) {
-			btrfs_page_clear_uptodate(fs_info, page, start, len);
+		if (error)
 			mapping_set_error(page->mapping, error);
-		}
 		btrfs_page_clear_writeback(fs_info, page, start, len);
 	}
 
@@ -1456,8 +1454,6 @@ done:
 	if (ret) {
 		btrfs_mark_ordered_io_finished(BTRFS_I(inode), page, page_start,
 					       PAGE_SIZE, !ret);
-		btrfs_page_clear_uptodate(btrfs_sb(inode->i_sb), page,
-					  page_start, PAGE_SIZE);
 		mapping_set_error(page->mapping, ret);
 	}
 	unlock_page(page);
@@ -1624,8 +1620,6 @@ static void extent_buffer_write_end_io(struct btrfs_bio *bbio)
 		struct page *page = bvec->bv_page;
 		u32 len = bvec->bv_len;
 
-		if (!uptodate)
-			btrfs_page_clear_uptodate(fs_info, page, start, len);
 		btrfs_page_clear_writeback(fs_info, page, start, len);
 		bio_offset += len;
 	}
@@ -2201,7 +2195,6 @@ void extent_write_locked_range(struct inode *inode, struct page *locked_page,
 		if (ret) {
 			btrfs_mark_ordered_io_finished(BTRFS_I(inode), page,
 						       cur, cur_len, !ret);
-			btrfs_page_clear_uptodate(fs_info, page, cur, cur_len);
 			mapping_set_error(page->mapping, ret);
 		}
 		btrfs_page_unlock_writer(fs_info, page, cur, cur_len);