Commit 164674a7 authored Sep 27, 2021 by Qu Wenruo Committed by David Sterba Oct 26, 2021

btrfs: handle page locking in btrfs_page_end_writer_lock with no writers



There are several call sites of extent_clear_unlock_delalloc() which get
@locked_page = NULL.
So that extent_clear_unlock_delalloc() will try to call
process_one_page() to unlock every page even the first page is not
locked by btrfs_page_start_writer_lock().

This will trigger an ASSERT() in btrfs_subpage_end_and_test_writer() as
previously we require every page passed to
btrfs_subpage_end_and_test_writer() to be locked by
btrfs_page_start_writer_lock().

But compression path doesn't go that way.

Thankfully it's not hard to distinguish page locked by lock_page() and
btrfs_page_start_writer_lock().

So do the check in btrfs_subpage_end_and_test_writer() so now it can
handle both cases well.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent e55a0de1

fs/btrfs/subpage.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -292,6 +292,16 @@ bool btrfs_subpage_end_and_test_writer(const struct btrfs_fs_info *fs_info,

		btrfs_subpage_assert(fs_info, page, start, len);

		/*
		* We have call sites passing @lock_page into
		* extent_clear_unlock_delalloc() for compression path.
		*
		* This @locked_page is locked by plain lock_page(), thus its
		* subpage::writers is 0. Handle them in a special way.
		*/
		if (atomic_read(&subpage->writers) == 0)
		return true;

		ASSERT(atomic_read(&subpage->writers) >= nbits);
		return atomic_sub_and_test(nbits, &subpage->writers);
		}