Commit e77751aa authored Dec 27, 2013 by Miao Xie Committed by Chris Mason Jan 28, 2014

Btrfs: fix the wrong nocow range check



The following warning message was outputed when running the 274th case
of xfstests with nodatacow option:
 BUG: Bad page state in process kswapd0  pfn:1c66f
 page:ffffea0000636848 count:0 mapcount:0 mapping:(null) index:0x78000
 page flags: 0x1000000000100a(error|uptodate|private_2)

It is because the check of nocow range was wrong, we should compare the
start and end position of the extent with the write position to verify
if the write position was in the extent, but the current code just used
the start postion to do the check, so we got the wrong extent and told
the caller that it was a nocow write. And then when we write back the
dirty pages, we found we should cow the extent, but at that time, there
was no space in the fs, we had to the error flag for the page. When
someone reclaimed that page, the above warning outputed. Fix it.

Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

parent 25e293c2

fs/btrfs/inode.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -6503,6 +6503,7 @@ noinline int can_nocow_extent(struct inode inode, u64 offset, u64 len,
		int slot;
		int found_type;
		bool nocow = (BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW);

		path = btrfs_alloc_path();
		if (!path)
		return -ENOMEM;
		@@ -6546,6 +6547,10 @@ noinline int can_nocow_extent(struct inode inode, u64 offset, u64 len,
		if (!nocow && found_type == BTRFS_FILE_EXTENT_REG)
		goto out;

		extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);
		if (extent_end <= offset)
		goto out;

		disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
		if (disk_bytenr == 0)
		goto out;
		@@ -6563,8 +6568,6 @@ noinline int can_nocow_extent(struct inode inode, u64 offset, u64 len,
		*ram_bytes = btrfs_file_extent_ram_bytes(leaf, fi);
		}

		extent_end = key.offset + btrfs_file_extent_num_bytes(leaf, fi);

		if (btrfs_extent_readonly(root, disk_bytenr))
		goto out;
		btrfs_release_path(path);

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