Merge tag 'xfs-4.18-fixes-2' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux

Pull xfs fixes from Darrick Wong:
 "Here are some patches for 4.18 to fix regressions, accounting
  problems, overflow problems, and to strengthen metadata validation to
  prevent corruption.

  This series has been run through a full xfstests run over the weekend
  and through a quick xfstests run against this morning's master, with
  no major failures reported.

  Changes since last update:

   - more metadata validation strengthening to prevent crashes.

   - fix extent offset overflow problem when insert_range on a 512b
     block fs

   - fix some off-by-one errors in the realtime fsmap code

   - fix some math errors in the default resblks calculation when free
     space is low

   - fix a problem where stale page contents are exposed via mmap read
     after a zero_range at eof

   - fix accounting problems with per-ag reservations causing statfs
     reports to vary incorrectly"

* tag 'xfs-4.18-fixes-2' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux:
  xfs: fix fdblocks accounting w/ RMAPBT per-AG reservation
  xfs: ensure post-EOF zeroing happens after zeroing part of a file
  xfs: fix off-by-one error in xfs_rtalloc_query_range
  xfs: fix uninitialized field in rtbitmap fsmap backend
  xfs: recheck reflink state after grabbing ILOCK_SHARED for a write
  xfs: don't allow insert-range to shift extents past the maximum offset
  xfs: don't trip over negative free space in xfs_reserve_blocks
  xfs: allow empty transactions while frozen
  xfs: xfs_iflush_abort() can be called twice on cluster writeback failure
  xfs: More robust inode extent count validation
  xfs: simplify xfs_bmap_punch_delalloc_range

12 files changed, 205 insertions, 130 deletions

diff --git a/fs/xfs/libxfs/xfs_ag_resv.c b/fs/xfs/libxfs/xfs_ag_resv.c
index 84db76e0e3e3..fecd187fcf2c 100644
--- a/fs/xfs/libxfs/xfs_ag_resv.c
+++ b/fs/xfs/libxfs/xfs_ag_resv.c
@@ -157,6 +157,7 @@ __xfs_ag_resv_free(
 	error = xfs_mod_fdblocks(pag->pag_mount, oldresv, true);
 	resv->ar_reserved = 0;
 	resv->ar_asked = 0;
+	resv->ar_orig_reserved = 0;
 
 	if (error)
 		trace_xfs_ag_resv_free_error(pag->pag_mount, pag->pag_agno,
@@ -189,13 +190,34 @@ __xfs_ag_resv_init(
 	struct xfs_mount		*mp = pag->pag_mount;
 	struct xfs_ag_resv		*resv;
 	int				error;
-	xfs_extlen_t			reserved;
+	xfs_extlen_t			hidden_space;
 
 	if (used > ask)
 		ask = used;
-	reserved = ask - used;
 
-	error = xfs_mod_fdblocks(mp, -(int64_t)reserved, true);
+	switch (type) {
+	case XFS_AG_RESV_RMAPBT:
+		/*
+		 * Space taken by the rmapbt is not subtracted from fdblocks
+		 * because the rmapbt lives in the free space.  Here we must
+		 * subtract the entire reservation from fdblocks so that we
+		 * always have blocks available for rmapbt expansion.
+		 */
+		hidden_space = ask;
+		break;
+	case XFS_AG_RESV_METADATA:
+		/*
+		 * Space taken by all other metadata btrees are accounted
+		 * on-disk as used space.  We therefore only hide the space
+		 * that is reserved but not used by the trees.
+		 */
+		hidden_space = ask - used;
+		break;
+	default:
+		ASSERT(0);
+		return -EINVAL;
+	}
+	error = xfs_mod_fdblocks(mp, -(int64_t)hidden_space, true);
 	if (error) {
 		trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agno,
 				error, _RET_IP_);
@@ -216,7 +238,8 @@ __xfs_ag_resv_init(
 
 	resv = xfs_perag_resv(pag, type);
 	resv->ar_asked = ask;
-	resv->ar_reserved = resv->ar_orig_reserved = reserved;
+	resv->ar_orig_reserved = hidden_space;
+	resv->ar_reserved = ask - used;
 
 	trace_xfs_ag_resv_init(pag, type, ask);
 	return 0;
diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 01628f0c9a0c..7205268b30bc 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -5780,6 +5780,32 @@ del_cursor:
 	return error;
 }
 
+/* Make sure we won't be right-shifting an extent past the maximum bound. */
+int
+xfs_bmap_can_insert_extents(
+	struct xfs_inode	*ip,
+	xfs_fileoff_t		off,
+	xfs_fileoff_t		shift)
+{
+	struct xfs_bmbt_irec	got;
+	int			is_empty;
+	int			error = 0;
+
+	ASSERT(xfs_isilocked(ip, XFS_IOLOCK_EXCL));
+
+	if (XFS_FORCED_SHUTDOWN(ip->i_mount))
+		return -EIO;
+
+	xfs_ilock(ip, XFS_ILOCK_EXCL);
+	error = xfs_bmap_last_extent(NULL, ip, XFS_DATA_FORK, &got, &is_empty);
+	if (!error && !is_empty && got.br_startoff >= off &&
+	    ((got.br_startoff + shift) & BMBT_STARTOFF_MASK) < got.br_startoff)
+		error = -EINVAL;
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+
+	return error;
+}
+
 int
 xfs_bmap_insert_extents(
 	struct xfs_trans	*tp,
diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
index 99dddbd0fcc6..9b49ddf99c41 100644
--- a/fs/xfs/libxfs/xfs_bmap.h
+++ b/fs/xfs/libxfs/xfs_bmap.h
@@ -227,6 +227,8 @@ int	xfs_bmap_collapse_extents(struct xfs_trans *tp, struct xfs_inode *ip,
 		xfs_fileoff_t *next_fsb, xfs_fileoff_t offset_shift_fsb,
 		bool *done, xfs_fsblock_t *firstblock,
 		struct xfs_defer_ops *dfops);
+int	xfs_bmap_can_insert_extents(struct xfs_inode *ip, xfs_fileoff_t off,
+		xfs_fileoff_t shift);
 int	xfs_bmap_insert_extents(struct xfs_trans *tp, struct xfs_inode *ip,
 		xfs_fileoff_t *next_fsb, xfs_fileoff_t offset_shift_fsb,
 		bool *done, xfs_fileoff_t stop_fsb, xfs_fsblock_t *firstblock,
diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
index 1c5a8aaf2bfc..059bc44c27e8 100644
--- a/fs/xfs/libxfs/xfs_format.h
+++ b/fs/xfs/libxfs/xfs_format.h
@@ -962,6 +962,9 @@ typedef enum xfs_dinode_fmt {
 		XFS_DFORK_DSIZE(dip, mp) : \
 		XFS_DFORK_ASIZE(dip, mp))
 
+#define XFS_DFORK_MAXEXT(dip, mp, w) \
+	(XFS_DFORK_SIZE(dip, mp, w) / sizeof(struct xfs_bmbt_rec))
+
 /*
  * Return pointers to the data or attribute forks.
  */
@@ -1526,6 +1529,8 @@ typedef struct xfs_bmdr_block {
 #define BMBT_STARTBLOCK_BITLEN	52
 #define BMBT_BLOCKCOUNT_BITLEN	21
 
+#define BMBT_STARTOFF_MASK	((1ULL << BMBT_STARTOFF_BITLEN) - 1)
+
 typedef struct xfs_bmbt_rec {
 	__be64			l0, l1;
 } xfs_bmbt_rec_t;
diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
index d38d724534c4..33dc34655ac3 100644
--- a/fs/xfs/libxfs/xfs_inode_buf.c
+++ b/fs/xfs/libxfs/xfs_inode_buf.c
@@ -374,6 +374,47 @@ xfs_log_dinode_to_disk(
 	}
 }
 
+static xfs_failaddr_t
+xfs_dinode_verify_fork(
+	struct xfs_dinode	*dip,
+	struct xfs_mount	*mp,
+	int			whichfork)
+{
+	uint32_t		di_nextents = XFS_DFORK_NEXTENTS(dip, whichfork);
+
+	switch (XFS_DFORK_FORMAT(dip, whichfork)) {
+	case XFS_DINODE_FMT_LOCAL:
+		/*
+		 * no local regular files yet
+		 */
+		if (whichfork == XFS_DATA_FORK) {
+			if (S_ISREG(be16_to_cpu(dip->di_mode)))
+				return __this_address;
+			if (be64_to_cpu(dip->di_size) >
+					XFS_DFORK_SIZE(dip, mp, whichfork))
+				return __this_address;
+		}
+		if (di_nextents)
+			return __this_address;
+		break;
+	case XFS_DINODE_FMT_EXTENTS:
+		if (di_nextents > XFS_DFORK_MAXEXT(dip, mp, whichfork))
+			return __this_address;
+		break;
+	case XFS_DINODE_FMT_BTREE:
+		if (whichfork == XFS_ATTR_FORK) {
+			if (di_nextents > MAXAEXTNUM)
+				return __this_address;
+		} else if (di_nextents > MAXEXTNUM) {
+			return __this_address;
+		}
+		break;
+	default:
+		return __this_address;
+	}
+	return NULL;
+}
+
 xfs_failaddr_t
 xfs_dinode_verify(
 	struct xfs_mount	*mp,
@@ -441,24 +482,9 @@ xfs_dinode_verify(
 	case S_IFREG:
 	case S_IFLNK:
 	case S_IFDIR:
-		switch (dip->di_format) {
-		case XFS_DINODE_FMT_LOCAL:
-			/*
-			 * no local regular files yet
-			 */
-			if (S_ISREG(mode))
-				return __this_address;
-			if (di_size > XFS_DFORK_DSIZE(dip, mp))
-				return __this_address;
-			if (dip->di_nextents)
-				return __this_address;
-			/* fall through */
-		case XFS_DINODE_FMT_EXTENTS:
-		case XFS_DINODE_FMT_BTREE:
-			break;
-		default:
-			return __this_address;
-		}
+		fa = xfs_dinode_verify_fork(dip, mp, XFS_DATA_FORK);
+		if (fa)
+			return fa;
 		break;
 	case 0:
 		/* Uninitialized inode ok. */
@@ -468,17 +494,9 @@ xfs_dinode_verify(
 	}
 
 	if (XFS_DFORK_Q(dip)) {
-		switch (dip->di_aformat) {
-		case XFS_DINODE_FMT_LOCAL:
-			if (dip->di_anextents)
-				return __this_address;
-		/* fall through */
-		case XFS_DINODE_FMT_EXTENTS:
-		case XFS_DINODE_FMT_BTREE:
-			break;
-		default:
-			return __this_address;
-		}
+		fa = xfs_dinode_verify_fork(dip, mp, XFS_ATTR_FORK);
+		if (fa)
+			return fa;
 	} else {
 		/*
 		 * If there is no fork offset, this may be a freshly-made inode
diff --git a/fs/xfs/libxfs/xfs_rtbitmap.c b/fs/xfs/libxfs/xfs_rtbitmap.c
index 65fc4ed2e9a1..b228c821bae6 100644
--- a/fs/xfs/libxfs/xfs_rtbitmap.c
+++ b/fs/xfs/libxfs/xfs_rtbitmap.c
@@ -1029,8 +1029,8 @@ xfs_rtalloc_query_range(
 	if (low_rec->ar_startext >= mp->m_sb.sb_rextents ||
 	    low_rec->ar_startext == high_rec->ar_startext)
 		return 0;
-	if (high_rec->ar_startext >= mp->m_sb.sb_rextents)
-		high_rec->ar_startext = mp->m_sb.sb_rextents - 1;
+	if (high_rec->ar_startext > mp->m_sb.sb_rextents)
+		high_rec->ar_startext = mp->m_sb.sb_rextents;
 
 	/* Iterate the bitmap, looking for discrepancies. */
 	rtstart = low_rec->ar_startext;
diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index c35009a86699..83b1e8c6c18f 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -685,12 +685,10 @@ out_unlock_iolock:
 }
 
 /*
- * dead simple method of punching delalyed allocation blocks from a range in
- * the inode. Walks a block at a time so will be slow, but is only executed in
- * rare error cases so the overhead is not critical. This will always punch out
- * both the start and end blocks, even if the ranges only partially overlap
- * them, so it is up to the caller to ensure that partial blocks are not
- * passed in.
+ * Dead simple method of punching delalyed allocation blocks from a range in
+ * the inode.  This will always punch out both the start and end blocks, even
+ * if the ranges only partially overlap them, so it is up to the caller to
+ * ensure that partial blocks are not passed in.
  */
 int
 xfs_bmap_punch_delalloc_range(
@@ -698,63 +696,44 @@ xfs_bmap_punch_delalloc_range(
 	xfs_fileoff_t		start_fsb,
 	xfs_fileoff_t		length)
 {
-	xfs_fileoff_t		remaining = length;
+	struct xfs_ifork	*ifp = &ip->i_df;
+	xfs_fileoff_t		end_fsb = start_fsb + length;
+	struct xfs_bmbt_irec	got, del;
+	struct xfs_iext_cursor	icur;
 	int			error = 0;
 
 	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
 
-	do {
-		int		done;
-		xfs_bmbt_irec_t	imap;
-		int		nimaps = 1;
-		xfs_fsblock_t	firstblock;
-		struct xfs_defer_ops dfops;
+	if (!(ifp->if_flags & XFS_IFEXTENTS)) {
+		error = xfs_iread_extents(NULL, ip, XFS_DATA_FORK);
+		if (error)
+			return error;
+	}
 
-		/*
-		 * Map the range first and check that it is a delalloc extent
-		 * before trying to unmap the range. Otherwise we will be
-		 * trying to remove a real extent (which requires a
-		 * transaction) or a hole, which is probably a bad idea...
-		 */
-		error = xfs_bmapi_read(ip, start_fsb, 1, &imap, &nimaps,
-				       XFS_BMAPI_ENTIRE);
+	if (!xfs_iext_lookup_extent_before(ip, ifp, &end_fsb, &icur, &got))
+		return 0;
 
-		if (error) {
-			/* something screwed, just bail */
-			if (!XFS_FORCED_SHUTDOWN(ip->i_mount)) {
-				xfs_alert(ip->i_mount,
-			"Failed delalloc mapping lookup ino %lld fsb %lld.",
-						ip->i_ino, start_fsb);
-			}
-			break;
-		}
-		if (!nimaps) {
-			/* nothing there */
-			goto next_block;
-		}
-		if (imap.br_startblock != DELAYSTARTBLOCK) {
-			/* been converted, ignore */
-			goto next_block;
-		}
-		WARN_ON(imap.br_blockcount == 0);
+	while (got.br_startoff + got.br_blockcount > start_fsb) {
+		del = got;
+		xfs_trim_extent(&del, start_fsb, length);
 
 		/*
-		 * Note: while we initialise the firstblock/dfops pair, they
-		 * should never be used because blocks should never be
-		 * allocated or freed for a delalloc extent and hence we need
-		 * don't cancel or finish them after the xfs_bunmapi() call.
+		 * A delete can push the cursor forward. Step back to the
+		 * previous extent on non-delalloc or extents outside the
+		 * target range.
 		 */
-		xfs_defer_init(&dfops, &firstblock);
-		error = xfs_bunmapi(NULL, ip, start_fsb, 1, 0, 1, &firstblock,
-					&dfops, &done);
-		if (error)
-			break;
+		if (!del.br_blockcount ||
+		    !isnullstartblock(del.br_startblock)) {
+			if (!xfs_iext_prev_extent(ifp, &icur, &got))
+				break;
+			continue;
+		}
 
-		ASSERT(!xfs_defer_has_unfinished_work(&dfops));
-next_block:
-		start_fsb++;
-		remaining--;
-	} while(remaining > 0);
+		error = xfs_bmap_del_extent_delay(ip, XFS_DATA_FORK, &icur,
+						  &got, &del);
+		if (error || !xfs_iext_get_extent(ifp, &icur, &got))
+			break;
+	}
 
 	return error;
 }
@@ -1208,7 +1187,22 @@ xfs_free_file_space(
 		return 0;
 	if (offset + len > XFS_ISIZE(ip))
 		len = XFS_ISIZE(ip) - offset;
-	return iomap_zero_range(VFS_I(ip), offset, len, NULL, &xfs_iomap_ops);
+	error = iomap_zero_range(VFS_I(ip), offset, len, NULL, &xfs_iomap_ops);
+	if (error)
+		return error;
+
+	/*
+	 * If we zeroed right up to EOF and EOF straddles a page boundary we
+	 * must make sure that the post-EOF area is also zeroed because the
+	 * page could be mmap'd and iomap_zero_range doesn't do that for us.
+	 * Writeback of the eof page will do this, albeit clumsily.
+	 */
+	if (offset + len >= XFS_ISIZE(ip) && ((offset + len) & PAGE_MASK)) {
+		error = filemap_write_and_wait_range(VFS_I(ip)->i_mapping,
+				(offset + len) & ~PAGE_MASK, LLONG_MAX);
+	}
+
+	return error;
 }
 
 /*
@@ -1404,6 +1398,10 @@ xfs_insert_file_space(
 
 	trace_xfs_insert_file_space(ip);
 
+	error = xfs_bmap_can_insert_extents(ip, stop_fsb, shift_fsb);
+	if (error)
+		return error;
+
 	error = xfs_prepare_shift(ip, offset);
 	if (error)
 		return error;
diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c
index c34fa9c342f2..c7157bc48bd1 100644
--- a/fs/xfs/xfs_fsmap.c
+++ b/fs/xfs/xfs_fsmap.c
@@ -513,8 +513,8 @@ xfs_getfsmap_rtdev_rtbitmap_query(
 	struct xfs_trans		*tp,
 	struct xfs_getfsmap_info	*info)
 {
-	struct xfs_rtalloc_rec		alow;
-	struct xfs_rtalloc_rec		ahigh;
+	struct xfs_rtalloc_rec		alow = { 0 };
+	struct xfs_rtalloc_rec		ahigh = { 0 };
 	int				error;
 
 	xfs_ilock(tp->t_mountp->m_rbmip, XFS_ILOCK_SHARED);
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index a7afcad6b711..3f2bd6032cf8 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -387,7 +387,7 @@ xfs_reserve_blocks(
 	do {
 		free = percpu_counter_sum(&mp->m_fdblocks) -
 						mp->m_alloc_set_aside;
-		if (!free)
+		if (free <= 0)
 			break;
 
 		delta = request - mp->m_resblks;
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 7a96c4e0ab5c..5df4de666cc1 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -3236,7 +3236,6 @@ xfs_iflush_cluster(
 	struct xfs_inode	*cip;
 	int			nr_found;
 	int			clcount = 0;
-	int			bufwasdelwri;
 	int			i;
 
 	pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ip->i_ino));
@@ -3360,37 +3359,22 @@ cluster_corrupt_out:
 	 * inode buffer and shut down the filesystem.
 	 */
 	rcu_read_unlock();
-	/*
-	 * Clean up the buffer.  If it was delwri, just release it --
-	 * brelse can handle it with no problems.  If not, shut down the
-	 * filesystem before releasing the buffer.
-	 */
-	bufwasdelwri = (bp->b_flags & _XBF_DELWRI_Q);
-	if (bufwasdelwri)
-		xfs_buf_relse(bp);
-
 	xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
 
-	if (!bufwasdelwri) {
-		/*
-		 * Just like incore_relse: if we have b_iodone functions,
-		 * mark the buffer as an error and call them.  Otherwise
-		 * mark it as stale and brelse.
-		 */
-		if (bp->b_iodone) {
-			bp->b_flags &= ~XBF_DONE;
-			xfs_buf_stale(bp);
-			xfs_buf_ioerror(bp, -EIO);
-			xfs_buf_ioend(bp);
-		} else {
-			xfs_buf_stale(bp);
-			xfs_buf_relse(bp);
-		}
-	}
-
 	/*
-	 * Unlocks the flush lock
+	 * We'll always have an inode attached to the buffer for completion
+	 * process by the time we are called from xfs_iflush(). Hence we have
+	 * always need to do IO completion processing to abort the inodes
+	 * attached to the buffer.  handle them just like the shutdown case in
+	 * xfs_buf_submit().
 	 */
+	ASSERT(bp->b_iodone);
+	bp->b_flags &= ~XBF_DONE;
+	xfs_buf_stale(bp);
+	xfs_buf_ioerror(bp, -EIO);
+	xfs_buf_ioend(bp);
+
+	/* abort the corrupt inode, as it was not attached to the buffer */
 	xfs_iflush_abort(cip, false);
 	kmem_free(cilist);
 	xfs_perag_put(pag);
@@ -3486,12 +3470,17 @@ xfs_iflush(
 		xfs_log_force(mp, 0);
 
 	/*
-	 * inode clustering:
-	 * see if other inodes can be gathered into this write
+	 * inode clustering: try to gather other inodes into this write
+	 *
+	 * Note: Any error during clustering will result in the filesystem
+	 * being shut down and completion callbacks run on the cluster buffer.
+	 * As we have already flushed and attached this inode to the buffer,
+	 * it has already been aborted and released by xfs_iflush_cluster() and
+	 * so we have no further error handling to do here.
 	 */
 	error = xfs_iflush_cluster(ip, bp);
 	if (error)
-		goto cluster_corrupt_out;
+		return error;
 
 	*bpp = bp;
 	return 0;
@@ -3500,12 +3489,8 @@ corrupt_out:
 	if (bp)
 		xfs_buf_relse(bp);
 	xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
-cluster_corrupt_out:
-	error = -EFSCORRUPTED;
 abort_out:
-	/*
-	 * Unlocks the flush lock
-	 */
+	/* abort the corrupt inode, as it was not attached to the buffer */
 	xfs_iflush_abort(ip, false);
 	return error;
 }
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 49f5492eed3b..55876dd02f0c 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -963,12 +963,13 @@ xfs_ilock_for_iomap(
 	unsigned		*lockmode)
 {
 	unsigned		mode = XFS_ILOCK_SHARED;
+	bool			is_write = flags & (IOMAP_WRITE | IOMAP_ZERO);
 
 	/*
 	 * COW writes may allocate delalloc space or convert unwritten COW
 	 * extents, so we need to make sure to take the lock exclusively here.
 	 */
-	if (xfs_is_reflink_inode(ip) && (flags & (IOMAP_WRITE | IOMAP_ZERO))) {
+	if (xfs_is_reflink_inode(ip) && is_write) {
 		/*
 		 * FIXME: It could still overwrite on unshared extents and not
 		 * need allocation.
@@ -989,6 +990,7 @@ xfs_ilock_for_iomap(
 		mode = XFS_ILOCK_EXCL;
 	}
 
+relock:
 	if (flags & IOMAP_NOWAIT) {
 		if (!xfs_ilock_nowait(ip, mode))
 			return -EAGAIN;
@@ -996,6 +998,17 @@ xfs_ilock_for_iomap(
 		xfs_ilock(ip, mode);
 	}
 
+	/*
+	 * The reflink iflag could have changed since the earlier unlocked
+	 * check, so if we got ILOCK_SHARED for a write and but we're now a
+	 * reflink inode we have to switch to ILOCK_EXCL and relock.
+	 */
+	if (mode == XFS_ILOCK_SHARED && is_write && xfs_is_reflink_inode(ip)) {
+		xfs_iunlock(ip, mode);
+		mode = XFS_ILOCK_EXCL;
+		goto relock;
+	}
+
 	*lockmode = mode;
 	return 0;
 }
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index e040af120b69..524f543c5b82 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -258,7 +258,12 @@ xfs_trans_alloc(
 	if (!(flags & XFS_TRANS_NO_WRITECOUNT))
 		sb_start_intwrite(mp->m_super);
 
-	WARN_ON(mp->m_super->s_writers.frozen == SB_FREEZE_COMPLETE);
+	/*
+	 * Zero-reservation ("empty") transactions can't modify anything, so
+	 * they're allowed to run while we're frozen.
+	 */
+	WARN_ON(resp->tr_logres > 0 &&
+		mp->m_super->s_writers.frozen == SB_FREEZE_COMPLETE);
 	atomic_inc(&mp->m_active_trans);
 
 	tp = kmem_zone_zalloc(xfs_trans_zone,