[RFC PATCH] xfs: Properly retry failed dquot items in case of error during buffer writeback

[Carlos Maiolino <cmaiolino@redhat.com>]

Hi,

Once the fix for inode item writeback errors is already queued
(d3a304b62), I believe it's time to fix the same problem in dquot code.

Although there were no reports of users hitting this bug in dquot code
(at least none I've seen), the bug is there and I was already planning
to fix it when the correct approach to fix the inodes part was decided.

So, this is an RFC patch to fix the same problem in dquot code,
regarding failed buffers being unable to be resubmitted once they are
flush locked.

The semantics are quite similar to inode items path, although during
xfs_qm_dqflush_done(), I'm not sure if the changes I made are correct.

Comments much appreciated :)


BTW, This patch should be applied only over branch xfs-4.14-merge, it requires
my previous patches, which are not in the master branch yet.

Cheers.

Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
---
 fs/xfs/xfs_dquot.c      | 11 ++++++++---
 fs/xfs/xfs_dquot_item.c | 37 +++++++++++++++++++++++++++++++++++--
 2 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c
index fd2ef8c2c9a7..8198c20212a2 100644
--- a/fs/xfs/xfs_dquot.c
+++ b/fs/xfs/xfs_dquot.c
@@ -987,14 +987,19 @@ xfs_qm_dqflush_done(
 	 * holding the lock before removing the dquot from the AIL.
 	 */
 	if ((lip->li_flags & XFS_LI_IN_AIL) &&
-	    lip->li_lsn == qip->qli_flush_lsn) {
+	   (lip->li_lsn == qip->qli_flush_lsn) ||
+	    lip->li_flags & XFS_LI_FAILED) {
 
 		/* xfs_trans_ail_delete() drops the AIL lock. */
 		spin_lock(&ailp->xa_lock);
-		if (lip->li_lsn == qip->qli_flush_lsn)
+		if (lip->li_lsn == qip->qli_flush_lsn) {
 			xfs_trans_ail_delete(ailp, lip, SHUTDOWN_CORRUPT_INCORE);
-		else
+		} else if (lip->li_flags & XFS_LI_FAILED) {
+			xfs_clear_li_failed(lip);
 			spin_unlock(&ailp->xa_lock);
+		} else {
+			spin_unlock(&ailp->xa_lock);
+		}
 	}
 
 	/*
diff --git a/fs/xfs/xfs_dquot_item.c b/fs/xfs/xfs_dquot_item.c
index 2c7a1629e064..35fd6d71bc42 100644
--- a/fs/xfs/xfs_dquot_item.c
+++ b/fs/xfs/xfs_dquot_item.c
@@ -137,6 +137,23 @@ xfs_qm_dqunpin_wait(
 	wait_event(dqp->q_pinwait, (atomic_read(&dqp->q_pincount) == 0));
 }
 
+/*
+ * Callback used to mark a buffer with XFS_LI_FAILED when items in the buffer
+ * have been failed during writeback
+ *
+ * this informs the AIL that the dquot is already flush locked on the next push,
+ * and acquires a hold on the buffer to ensure that it isn't reclaimed before
+ * dirty data makes it to disk.
+ */
+STATIC void
+xfs_dquot_item_error(
+	struct xfs_log_item	*lip,
+	struct xfs_buf		*bp)
+{
+	ASSERT(XFS_DQ_IS_LOCKED(DQUOT_ITEM(lip)->qli_item));
+	xfs_set_li_failed(lip, bp);
+}
+
 STATIC uint
 xfs_qm_dquot_logitem_push(
 	struct xfs_log_item	*lip,
@@ -144,13 +161,28 @@ xfs_qm_dquot_logitem_push(
 					      __acquires(&lip->li_ailp->xa_lock)
 {
 	struct xfs_dquot	*dqp = DQUOT_ITEM(lip)->qli_dquot;
-	struct xfs_buf		*bp = NULL;
+	struct xfs_buf		*bp = lip->li_buf;
 	uint			rval = XFS_ITEM_SUCCESS;
 	int			error;
 
 	if (atomic_read(&dqp->q_pincount) > 0)
 		return XFS_ITEM_PINNED;
 
+	/*
+	 * The buffer containing this item failed to be written back
+	 * previously. Resubmit the buffer for IO
+	 */
+	if (lip->li_flags & XFS_LI_FAILED) {
+		if (!xfs_buf_trylock(bp))
+			return XFS_ITEM_LOCKED;
+
+		if (!xfs_buf_resubmit_failed_buffers(bp, lip, buffer_list))
+			rval = XFS_ITEM_FLUSHING;
+
+		xfs_buf_unlock(bp);
+		return rval;
+	}
+
 	if (!xfs_dqlock_nowait(dqp))
 		return XFS_ITEM_LOCKED;
 
@@ -242,7 +274,8 @@ static const struct xfs_item_ops xfs_dquot_item_ops = {
 	.iop_unlock	= xfs_qm_dquot_logitem_unlock,
 	.iop_committed	= xfs_qm_dquot_logitem_committed,
 	.iop_push	= xfs_qm_dquot_logitem_push,
-	.iop_committing = xfs_qm_dquot_logitem_committing
+	.iop_committing = xfs_qm_dquot_logitem_committing,
+	.iop_error	= xfs_dquot_item_error
 };
 
 /*
-- 
2.13.5