[PATCH 5.17 045/772] btrfs: fix the error handling for submit_extent_page() for btrfs_do_readpage()

Greg Kroah-Hartman
2022-06-07T20:21:51Z

From: Qu Wenruo <wqu@suse.com>

commit 10f7f6f879c28f8368d6516ab1ccf3517a1f5d3d upstream.

[BUG]
Test case generic/475 have a very high chance (almost 100%) to hit a fs
hang, where a data page will never be unlocked and hang all later
operations.

[CAUSE]
In btrfs_do_readpage(), if we hit an error from submit_extent_page() we
will try to do the cleanup for our current io range, and exit.

This works fine for PAGE_SIZE == sectorsize cases, but not for subpage.

For subpage btrfs_do_readpage() will lock the full page first, which can
contain several different sectors and extents:

btrfs_do_readpage()
|- begin_page_read()
| |- btrfs_subpage_start_reader();
| Now the page will have PAGE_SIZE / sectorsize reader pending,
| and the page is locked.
|
|- end_page_read() for different branches
| This function will reduce subpage readers, and when readers
| reach 0, it will unlock the page.

But when submit_extent_page() failed, we only cleanup the current
io range, while the remaining io range will never be cleaned up, and the
page remains locked forever.

[FIX]
Update the error handling of submit_extent_page() to cleanup all the
remaining subpage range before exiting the loop.

Please note that, now submit_extent_page() can only fail due to
sanity check in alloc_new_bio().

Thus regular IO errors are impossible to trigger the error path.

CC: stable@vger.kernel.org # 5.15+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/btrfs/extent_io.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3721,8 +3721,12 @@ int btrfs_do_readpage(struct page *page,
this_bio_flag,
force_bio_submit);
if (ret) {
- unlock_extent(tree, cur, cur + iosize - 1);
- end_page_read(page, false, cur, iosize);
+ /*
+ * We have to unlock the remaining range, or the page
+ * will never be unlocked.
+ */
+ unlock_extent(tree, cur, end);
+ end_page_read(page, false, cur, end + 1 - cur);
goto out;
}
cur = cur + iosize;