Patch "Btrfs: adjust outstanding_extents counter properly when dio write is split" has been added to the 4.4-stable tree

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

Btrfs: adjust outstanding_extents counter properly when dio write is split

to the 4.4-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-adjust-outstanding_extents-counter-properly-when-dio-write-is-split.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Liu Bo <[email protected]>
Date: Thu, 22 Dec 2016 17:13:54 -0800
Subject: Btrfs: adjust outstanding_extents counter properly when dio write is split

From: Liu Bo <[email protected]>

[ Upstream commit c2931667c83ded6504b3857e99cc45b21fa496fb ]

Currently how btrfs dio deals with split dio write is not good enough if dio write is split into several segments due to the lack of contiguous space, a large dio write like 'dd bs=1G count=1' can end up with incorrect outstanding_extents counter and endio would complain loudly with an assertion.

This fixes the problem by compensating the outstanding_extents counter in inode if a large dio write gets split.

---
 fs/btrfs/inode.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

@@ -7521,11 +7521,18 @@ static void adjust_dio_outstanding_exten
 	 * within our reservation, otherwise we need to adjust our inode
 	 * counter appropriately.
 	 */
-	if (dio_data->outstanding_extents) {
+	if (dio_data->outstanding_extents >= num_extents) {
 		dio_data->outstanding_extents -= num_extents;
 	} else {
+		/*
+		 * If dio write length has been split due to no large enough
+		 * contiguous space, we need to compensate our inode counter
+		 * appropriately.
+		 */
+		u64 num_needed = num_extents - dio_data->outstanding_extents;
+
 		spin_lock(&BTRFS_I(inode)->lock);
-		BTRFS_I(inode)->outstanding_extents += num_extents;
+		BTRFS_I(inode)->outstanding_extents += num_needed;
 		spin_unlock(&BTRFS_I(inode)->lock);
 	}
 }

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

queue-4.4/btrfs-adjust-outstanding_extents-counter-properly-when-dio-write-is-split.patch queue-4.4/btrfs-use-down_read_nested-to-make-lockdep-silent.patch