[PATCH v4 05/18] btrfs: make grab_extent_buffer_from_page() to handle subpage case

[Qu Wenruo]

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

Thankfully we have radix tree lock protecting us from inserting the same
eb into the tree.

Thus we don't really need to do the extra hassle, just let
alloc_extent_buffer() to handle existing eb in radix tree.

Now if two ebs are being allocated as the same time, one will fail with
-EEIXST when inserting its eb into the radix tree.

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

Signed-off-by: Qu Wenruo <w...@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 320731487ac0..b2f8ac5e9a9e 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5282,10 +5282,19 @@ 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;
@@ -5366,7 +5375,7 @@ 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);
-- 
2.30.0