In cow_file_range(), after we have succeeded creating an inline extent,
we unlock the page with extent_clear_unlock_delalloc() by passing
locked_page == NULL.
For sectorsize == PAGE_SIZE case, this is just making the page lock and
unlock harder to grab.
But for incoming subpage case, it can be a big problem.
For incoming subpage case, page locking have two entrace:
- __process_pages_contig()
In that case, we know exactly the range we want to lock (which only
requires sector alignment).
To handle the subpage requirement, we introduce btrfs_subpage::writers
to page::private, and will update it in __process_pages_contig().
- Other directly lock/unlock_page() call sites
Those won't touch btrfs_subpage::writers at all.
This means, page locked by __process_pages_contig() can only be unlocked
by __process_pages_contig().
Thankfully we already have the existing infrastructure in the form of
@locked_page in various call sites.
Unfortunately, extent_clear_unlock_delalloc() in cow_file_range() after
creating an inline extent is the exception.
It intentionally call extent_clear_unlock_delalloc() with locked_page ==
NULL, to also unlock current page (and clear its dirty/writeback bits).
To co-operate with incoming subpage modifications, and make the page
lock/unlock pair easier to understand, this patch will still call
extent_clear_unlock_delalloc() with locked_page, and only unlock the
page in __extent_writepage().
Signed-off-by: Qu Wenruo <w...@suse.com>
---
fs/btrfs/inode.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index f366dc2fb1ff..566431d7b257 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1072,7 +1072,8 @@ static noinline int cow_file_range(struct btrfs_inode
*inode,
* our outstanding extent for clearing delalloc for this
* range.
*/
- extent_clear_unlock_delalloc(inode, start, end, NULL,
+ extent_clear_unlock_delalloc(inode, start, end,
+ locked_page,
EXTENT_LOCKED | EXTENT_DELALLOC |
EXTENT_DELALLOC_NEW | EXTENT_DEFRAG |
EXTENT_DO_ACCOUNTING, PAGE_UNLOCK |
@@ -1080,6 +1081,19 @@ static noinline int cow_file_range(struct btrfs_inode
*inode,
*nr_written = *nr_written +
(end - start + PAGE_SIZE) / PAGE_SIZE;
*page_started = 1;
+ /*
+ * locked_page is locked by the caller of
+ * writepage_delalloc(), not locked by
+ * __process_pages_contig().
+ *
+ * We can't let __process_pages_contig() to unlock it,
+ * as it doesn't have any subpage::writers recorded.
+ *
+ * Here we manually unlock the page, since the caller
+ * can't use page_started to determine if it's an
+ * inline extent or a compressed extent.
+ */
+ unlock_page(locked_page);
goto out;
} else if (ret < 0) {
goto out_unlock;
--
2.31.1
