Btrfs: adjust outstanding_extents counter properly when dio write is split

[ 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.

Reported-by: Anand Jain <anand.jain@oracle.com>
Tested-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a2a014b..8a05fa7 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7648,11 +7648,18 @@ static void adjust_dio_outstanding_extents(struct inode *inode,
         * 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);
        }
 }