From 0f6925fa2907df58496cabc33fa4677c635e2223 Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Wed, 14 Oct 2015 15:26:13 +0800 Subject: [PATCH] btrfs: Avoid truncate tailing page if fallocate range doesn't exceed inode size Current code will always truncate tailing page if its alloc_start is smaller than inode size. For example, the file extent layout is like: 0 4K 8K 16K 32K |<-----Extent A---------------->| |<--Inode size: 18K---------->| But if calling fallocate even for range [0,4K), it will cause btrfs to re-truncate the range [16,32K), causing COW and a new extent. 0 4K 8K 16K 32K |///////| <- Fallocate call range |<-----Extent A-------->|<--B-->| The cause is quite easy, just a careless btrfs_truncate_inode() in a else branch without extra judgment. Fix it by add judgment on whether the fallocate range is beyond isize. Signed-off-by: Qu Wenruo Signed-off-by: Chris Mason --- fs/btrfs/file.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index b823fac91c92..8c6f247ba81d 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -2584,7 +2584,7 @@ static long btrfs_fallocate(struct file *file, int mode, alloc_start); if (ret) goto out; - } else { + } else if (offset + len > inode->i_size) { /* * If we are fallocating from the end of the file onward we * need to zero out the end of the page if i_size lands in the -- 2.20.1