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[PATCH 3.18 30/33] xfs: fix up quotacheck buffer list error handling

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3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Brian Foster <bfoster@redhat.com>

commit 20e8a063786050083fe05b4f45be338c60b49126 upstream.

The quotacheck error handling of the delwri buffer list assumes the
resident buffers are locked and doesn't clear the _XBF_DELWRI_Q flag
on the buffers that are dequeued. This can lead to assert failures
on buffer release and possibly other locking problems.

Move this code to a delwri queue cancel helper function to
encapsulate the logic required to properly release buffers from a
delwri queue. Update the helper to clear the delwri queue flag and
call it from quotacheck.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/xfs/xfs_buf.c |   24 ++++++++++++++++++++++++
 fs/xfs/xfs_buf.h |    1 +
 fs/xfs/xfs_qm.c  |    7 +------
 3 files changed, 26 insertions(+), 6 deletions(-)

--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -982,6 +982,8 @@ void
 xfs_buf_unlock(
 	struct xfs_buf		*bp)
 {
+	ASSERT(xfs_buf_islocked(bp));
+
 	XB_CLEAR_OWNER(bp);
 	up(&bp->b_sema);
 
@@ -1698,6 +1700,28 @@ error:
 }
 
 /*
+ * Cancel a delayed write list.
+ *
+ * Remove each buffer from the list, clear the delwri queue flag and drop the
+ * associated buffer reference.
+ */
+void
+xfs_buf_delwri_cancel(
+	struct list_head	*list)
+{
+	struct xfs_buf		*bp;
+
+	while (!list_empty(list)) {
+		bp = list_first_entry(list, struct xfs_buf, b_list);
+
+		xfs_buf_lock(bp);
+		bp->b_flags &= ~_XBF_DELWRI_Q;
+		list_del_init(&bp->b_list);
+		xfs_buf_relse(bp);
+	}
+}
+
+/*
  * Add a buffer to the delayed write list.
  *
  * This queues a buffer for writeout if it hasn't already been.  Note that
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -302,6 +302,7 @@ extern void xfs_buf_iomove(xfs_buf_t *,
 extern xfs_caddr_t xfs_buf_offset(xfs_buf_t *, size_t);
 
 /* Delayed Write Buffer Routines */
+extern void xfs_buf_delwri_cancel(struct list_head *);
 extern bool xfs_buf_delwri_queue(struct xfs_buf *, struct list_head *);
 extern int xfs_buf_delwri_submit(struct list_head *);
 extern int xfs_buf_delwri_submit_nowait(struct list_head *);
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -1359,12 +1359,7 @@ xfs_qm_quotacheck(
 	mp->m_qflags |= flags;
 
  error_return:
-	while (!list_empty(&buffer_list)) {
-		struct xfs_buf *bp =
-			list_first_entry(&buffer_list, struct xfs_buf, b_list);
-		list_del_init(&bp->b_list);
-		xfs_buf_relse(bp);
-	}
+	xfs_buf_delwri_cancel(&buffer_list);
 
 	if (error) {
 		xfs_warn(mp,

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[PATCH 3.18 00/33] 3.18.56-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 18:20 +0200
  [PATCH 3.18 06/33] s390/qeth: avoid null pointer dereference on OSN Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 18:20 +0200
  [PATCH 3.18 23/33] mm/migrate: fix refcount handling when !hugepage_migration_supported() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 18:20 +0200
  [PATCH 3.18 20/33] ALSA: hda - apply STAC_9200_DELL_M22 quirk for Dell Latitude D430 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 18:20 +0200
  [PATCH 3.18 12/33] ipv6: Check ip6_find_1stfragopt() return value properly. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 18:20 +0200
  [PATCH 3.18 16/33] sctp: fix ICMP processing if skb is non-linear Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 18:20 +0200
  [PATCH 3.18 30/33] xfs: fix up quotacheck buffer list error handling Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 18:20 +0200
  [PATCH 3.18 22/33] drm/gma500/psb: Actually use VBT mode when it is found Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 18:30 +0200
  [PATCH 3.18 33/33] xfs: fix unaligned access in xfs_btree_visit_blocks Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 19:40 +0200
  [PATCH 3.18 08/33] sctp: fix src address selection if using secondary addresses for ipv6 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 19:40 +0200
  [PATCH 3.18 14/33] ipv6: fix out of bound writes in __ip6_append_data() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 19:40 +0200
  [PATCH 3.18 29/33] xfs: prevent multi-fsb dir readahead from reading random blocks Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 19:40 +0200
  [PATCH 3.18 32/33] xfs: bad assertion for delalloc an extent that start at i_size Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 19:40 +0200
  [PATCH 3.18 27/33] xfs: fix over-copying of getbmap parameters from userspace Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 19:40 +0200
  [PATCH 3.18 21/33] slub/memcg: cure the brainless abuse of sysfs attributes Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 19:40 +0200
  [PATCH 3.18 31/33] xfs: fix indlen accounting error on partial delalloc conversion Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-05 19:40 +0200
  Re: [PATCH 3.18 01/33] Revert "stackprotector: Increase the per-task  stack canarys random range from 32 bits to 64 bits on 64-bit platforms" Kees Cook <keescook@chromium.org> - 2017-06-05 21:20 +0200
    Re: [kernel-hardening] Re: [PATCH 3.18 01/33] Revert  "stackprotector: Increase the per-task stack canarys random range from 32  bits to 64 bits on 64-bit platforms" Eric Biggers <ebiggers3@gmail.com> - 2017-06-05 22:10 +0200
      Re: [kernel-hardening] Re: [PATCH 3.18 01/33] Revert  "stackprotector: Increase the per-task stack canarys random range from 32  bits to 64 bits on 64-bit platforms" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-06 09:30 +0200
  Re: [PATCH 3.18 00/33] 3.18.56-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-06-05 22:40 +0200
  Re: [PATCH 3.18 00/33] 3.18.56-stable review Guenter Roeck <linux@roeck-us.net> - 2017-06-06 00:10 +0200
  Re: [PATCH 3.18 00/33] 3.18.56-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-06-06 09:30 +0200
    Re: [PATCH 3.18 00/33] 3.18.56-stable review Kevin Hilman <khilman@baylibre.com> - 2017-06-06 23:00 +0200

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