Merge tag 'xfs-5.13-merge-5' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux

Pull more xfs updates from Darrick Wong:
 "Except for the timestamp struct renaming patches, everything else in
  here are bug fixes:

   - Rename the log timestamp struct.

   - Remove broken transaction counter debugging that wasn't working
     correctly on very old filesystems.

   - Various fixes to make pre-lazysbcount filesystems work properly
     again.

   - Fix a free space accounting problem where we neglected to consider
     free space btree blocks that track metadata reservation space when
     deciding whether or not to allow caller to reserve space for a
     metadata update.

   - Fix incorrect pagecache clearing behavior during FUNSHARE ops.

   - Don't allow log writes if the data device is readonly"

* tag 'xfs-5.13-merge-5' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux:
  xfs: don't allow log writes if the data device is readonly
  xfs: fix xfs_reflink_unshare usage of filemap_write_and_wait_range
  xfs: set aside allocation btree blocks from block reservation
  xfs: introduce in-core global counter of allocbt blocks
  xfs: unconditionally read all AGFs on mounts with perag reservation
  xfs: count free space btree blocks when scrubbing pre-lazysbcount fses
  xfs: update superblock counters correctly for !lazysbcount
  xfs: don't check agf_btreeblks on pre-lazysbcount filesystems
  xfs: remove obsolete AGF counter debugging
  xfs: rename struct xfs_legacy_ictimestamp
  xfs: rename xfs_ictimestamp_t

1 files changed, 14 insertions, 1 deletions

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index cb1e2c4702c3..bdfee1943796 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1188,6 +1188,7 @@ xfs_mod_fdblocks(
 	int64_t			lcounter;
 	long long		res_used;
 	s32			batch;
+	uint64_t		set_aside;
 
 	if (delta > 0) {
 		/*
@@ -1227,8 +1228,20 @@ xfs_mod_fdblocks(
 	else
 		batch = XFS_FDBLOCKS_BATCH;
 
+	/*
+	 * Set aside allocbt blocks because these blocks are tracked as free
+	 * space but not available for allocation. Technically this means that a
+	 * single reservation cannot consume all remaining free space, but the
+	 * ratio of allocbt blocks to usable free blocks should be rather small.
+	 * The tradeoff without this is that filesystems that maintain high
+	 * perag block reservations can over reserve physical block availability
+	 * and fail physical allocation, which leads to much more serious
+	 * problems (i.e. transaction abort, pagecache discards, etc.) than
+	 * slightly premature -ENOSPC.
+	 */
+	set_aside = mp->m_alloc_set_aside + atomic64_read(&mp->m_allocbt_blks);
 	percpu_counter_add_batch(&mp->m_fdblocks, delta, batch);
-	if (__percpu_counter_compare(&mp->m_fdblocks, mp->m_alloc_set_aside,
+	if (__percpu_counter_compare(&mp->m_fdblocks, set_aside,
 				     XFS_FDBLOCKS_BATCH) >= 0) {
 		/* we had space! */
 		return 0;