Patch "Btrfs: fix delalloc accounting after copy_from_user faults" has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

Btrfs: fix delalloc accounting after copy_from_user faults

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
btrfs-fix-delalloc-accounting-after-copy_from_user-faults.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Chris Mason <[email protected]>
Date: Tue, 19 Jul 2016 05:52:36 -0700
Subject: Btrfs: fix delalloc accounting after copy_from_user faults

From: Chris Mason <[email protected]>

commit 8b8b08cbfb9021af4b54b4175fc4c51d655aac8c upstream.

Commit 56244ef151c3cd11 was almost but not quite enough to fix the reservation math after btrfs_copy_from_user returned partial copies.

Some users are still seeing warnings in btrfs_destroy_inode, and with a long enough test run I'm able to trigger them as well.

This patch fixes the accounting math again, bringing it much closer to the way it was before the sectorsize conversion Chandan did. The problem is accounting for the offset into the page/sector when we do a partial copy. This one just uses the dirty_sectors variable which should already be updated properly.

---
 fs/btrfs/file.c |   12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

@@ -1629,13 +1629,11 @@ again:
 		 * managed to copy.
 		 */
 		if (num_sectors > dirty_sectors) {
-			/*
-			 * we round down because we don't want to count
-			 * any partial blocks actually sent through the
-			 * IO machines
-			 */
-			release_bytes = round_down(release_bytes - copied,
-				      root->sectorsize);
+
+			/* release everything except the sectors we dirtied */
+			release_bytes -= dirty_sectors <<
+				root->fs_info->sb->s_blocksize_bits;
+
 			if (copied > 0) {
 				spin_lock(&BTRFS_I(inode)->lock);
 				BTRFS_I(inode)->outstanding_extents++;

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/btrfs-fix-delalloc-accounting-after-copy_from_user-faults.patch