From 4750af3bbe5d975951b09afc61f18c7b29db7d44 Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Mon, 31 May 2021 16:50:48 +0800 Subject: [PATCH] btrfs: prevent extent_clear_unlock_delalloc() to unlock page not locked by __process_pages_contig() 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 entry points: - __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(). Tested-by: Ritesh Harjani # [ppc64] Tested-by: Anand Jain # [aarch64] Signed-off-by: Qu Wenruo Signed-off-by: David Sterba --- 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 52f31d59..9f7b711 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -1091,7 +1091,8 @@ 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 | @@ -1099,6 +1100,19 @@ 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; -- 2.7.4