From: Qu Wenruo <quwenruo@cn.fujitsu.com>
Date: Thu, 29 Oct 2015 09:28:46 +0000 (+0800)
Subject: btrfs: Fix a data space underflow warning
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=485290a734f14279fa9376b3d6021a2dc1f82356;p=linux-beck.git

btrfs: Fix a data space underflow warning

Even with quota disabled, generic/127 will trigger a kernel warning by
underflow data space info.

The bug is caused by buffered write, which in case of short copy, the
start parameter for btrfs_delalloc_release_space() is wrong, and
round_up/down() in btrfs_delalloc_release() extents the range to page
aligned, decreasing one more page than expected.

This patch will fix it by passing correct start.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
---

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 381be79f779a..e6df6f1b13dd 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1604,12 +1604,17 @@ again:
 				BTRFS_I(inode)->outstanding_extents++;
 				spin_unlock(&BTRFS_I(inode)->lock);
 			}
-			if (only_release_metadata)
+			if (only_release_metadata) {
 				btrfs_delalloc_release_metadata(inode,
 								release_bytes);
-			else
-				btrfs_delalloc_release_space(inode, pos,
+			} else {
+				u64 __pos;
+
+				__pos = round_down(pos, root->sectorsize) +
+					(dirty_pages << PAGE_CACHE_SHIFT);
+				btrfs_delalloc_release_space(inode, __pos,
 							     release_bytes);
+			}
 		}
 
 		release_bytes = dirty_pages << PAGE_CACHE_SHIFT;