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 <quwenruo@xxxxxxxxxxxxxx>
---
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 b823fac..8c6f247 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
--
2.6.1
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