[PATCH 01/14] btrfs: extent_io: Use detach_page_private() for alloc_extent_buffer()

From: Qu Wenruo <wqu@suse.com>
To: linux-btrfs@vger.kernel.org
Subject: [PATCH 01/14] btrfs: extent_io: Use detach_page_private() for alloc_extent_buffer()
Date: Wed, 18 Nov 2020 16:53:06 +0800	[thread overview]
Message-ID: <20201118085319.56668-2-wqu@suse.com> (raw)
In-Reply-To: <20201118085319.56668-1-wqu@suse.com>

In alloc_extent_buffer(), after we got a page from btree inode, we check
if that page has private pointer attached.

If attached, we check if the existing extent buffer has a proper refs.
If not (the eb is being freed), we will detach that private eb pointer.

The point here is, we are detaching that eb pointer by calling:
- ClearPagePrivate()
- put_page()

The put_page() here is especially confusing, as it's decreaing the ref
caused by attach_page_private().
Without knowing that, it looks like the put_page() is for the
find_or_create_page() call, confusing the read.

Since we're always modifing page private with attach_page_private() and
detach_page_private(), the only open-coded detach_page_private() here is
really confusing.

Fix it by calling detach_page_private().

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index f305777ee1a3..55115f485d09 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5310,14 +5310,13 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 				goto free_eb;
 			}
 			exists = NULL;
+			WARN_ON(PageDirty(p));
 
 			/*
 			 * Do this so attach doesn't complain and we need to
 			 * drop the ref the old guy had.
 			 */
-			ClearPagePrivate(p);
-			WARN_ON(PageDirty(p));
-			put_page(p);
+			detach_page_private(page);
 		}
 		attach_extent_buffer_page(eb, p);
 		spin_unlock(&mapping->private_lock);
-- 
2.29.2

