[PATCH v3 09/22] btrfs: extent_io: make grab_extent_buffer_from_page() to handle subpage case

[Qu Wenruo <wqu@suse.com>]

For subpage case, grab_extent_buffer() can't really get an extent buffer
just from btrfs_subpage.

Although we have btrfs_subpage::tree_block_bitmap, which can be used to
grab the bytenr of an existing extent buffer, and can then go radix tree
search to grab that existing eb.

However we are still doing radix tree insert check in
alloc_extent_buffer(), thus we don't really need to do the extra hassle,
just let alloc_extent_buffer() to handle existing eb in radix tree.

So for grab_extent_buffer(), just always return NULL for subpage case.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 2eeff925450f..9b6b8f6b6da3 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5276,10 +5276,19 @@ struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
 }
 #endif
 
-static struct extent_buffer *grab_extent_buffer(struct page *page)
+static struct extent_buffer *grab_extent_buffer(
+		struct btrfs_fs_info *fs_info, struct page *page)
 {
 	struct extent_buffer *exists;
 
+	/*
+	 * For subpage case, we completely rely on radix tree to ensure we
+	 * don't try to insert two eb for the same bytenr.
+	 * So here we alwasy return NULL and just continue.
+	 */
+	if (fs_info->sectorsize < PAGE_SIZE)
+		return NULL;
+
 	/* Page not yet attached to an extent buffer */
 	if (!PagePrivate(page))
 		return NULL;
@@ -5357,7 +5366,7 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 		}
 
 		spin_lock(&mapping->private_lock);
-		exists = grab_extent_buffer(p);
+		exists = grab_extent_buffer(fs_info, p);
 		if (exists) {
 			spin_unlock(&mapping->private_lock);
 			unlock_page(p);
-- 
2.29.2