[PATCH 2/3] xfs: transaction subsystem quiesce mechanism

[Brian Foster <bfoster@redhat.com>]

The updated quotaoff logging algorithm depends on a runtime quiesce
of the transaction subsystem to guarantee all transactions after a
certain point detect quota subsystem changes. Implement this
mechanism using an internal lock, similar to the external filesystem
freeze mechanism. This is also somewhat analogous to the old percpu
transaction counter mechanism, but we don't actually need a counter.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/xfs_aops.c  |  2 ++
 fs/xfs/xfs_mount.h |  3 +++
 fs/xfs/xfs_super.c |  8 ++++++++
 fs/xfs/xfs_trans.c |  4 ++--
 fs/xfs/xfs_trans.h | 20 ++++++++++++++++++++
 5 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index b35611882ff9..214310c94de5 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -58,6 +58,7 @@ xfs_setfilesize_trans_alloc(
 	 * we released it.
 	 */
 	__sb_writers_release(ioend->io_inode->i_sb, SB_FREEZE_FS);
+	percpu_rwsem_release(&mp->m_trans_rwsem, true, _THIS_IP_);
 	/*
 	 * We hand off the transaction to the completion thread now, so
 	 * clear the flag here.
@@ -127,6 +128,7 @@ xfs_setfilesize_ioend(
 	 */
 	current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
 	__sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS);
+	percpu_rwsem_acquire(&ip->i_mount->m_trans_rwsem, true, _THIS_IP_);
 
 	/* we abort the update if there was an IO error */
 	if (error) {
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index dfa429b77ee2..f1083a9ce1f8 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -171,6 +171,9 @@ typedef struct xfs_mount {
 	 */
 	struct percpu_counter	m_delalloc_blks;
 
+	/* lock for transaction quiesce (used by quotaoff) */
+	struct percpu_rw_semaphore	m_trans_rwsem;
+
 	struct radix_tree_root	m_perag_tree;	/* per-ag accounting info */
 	spinlock_t		m_perag_lock;	/* lock for m_perag_tree */
 	uint64_t		m_resblks;	/* total reserved blocks */
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index baf5de30eebb..ff3ad5392e21 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1029,8 +1029,15 @@ xfs_init_percpu_counters(
 	if (error)
 		goto free_fdblocks;
 
+	/* not a counter, but close enough... */
+	error = percpu_init_rwsem(&mp->m_trans_rwsem);
+	if (error)
+		goto free_delalloc;
+
 	return 0;
 
+free_delalloc:
+	percpu_counter_destroy(&mp->m_delalloc_blks);
 free_fdblocks:
 	percpu_counter_destroy(&mp->m_fdblocks);
 free_ifree:
@@ -1053,6 +1060,7 @@ static void
 xfs_destroy_percpu_counters(
 	struct xfs_mount	*mp)
 {
+	percpu_free_rwsem(&mp->m_trans_rwsem);
 	percpu_counter_destroy(&mp->m_icount);
 	percpu_counter_destroy(&mp->m_ifree);
 	percpu_counter_destroy(&mp->m_fdblocks);
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index ca18a040336a..c07fa036549a 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -69,7 +69,7 @@ xfs_trans_free(
 
 	trace_xfs_trans_free(tp, _RET_IP_);
 	if (!(tp->t_flags & XFS_TRANS_NO_WRITECOUNT))
-		sb_end_intwrite(tp->t_mountp->m_super);
+		xfs_trans_end(tp->t_mountp);
 	xfs_trans_free_dqinfo(tp);
 	kmem_cache_free(xfs_trans_zone, tp);
 }
@@ -265,7 +265,7 @@ xfs_trans_alloc(
 	 */
 	tp = kmem_cache_zalloc(xfs_trans_zone, GFP_KERNEL | __GFP_NOFAIL);
 	if (!(flags & XFS_TRANS_NO_WRITECOUNT))
-		sb_start_intwrite(mp->m_super);
+		xfs_trans_start(mp);
 
 	/*
 	 * Zero-reservation ("empty") transactions can't modify anything, so
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index f46534b75236..af54c17a22c0 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -209,6 +209,26 @@ xfs_trans_read_buf(
 				      flags, bpp, ops);
 }
 
+/*
+ * Context tracking helpers for external (i.e. fs freeze) and internal
+ * transaction quiesce.
+ */
+static inline void
+xfs_trans_start(
+	struct xfs_mount	*mp)
+{
+	sb_start_intwrite(mp->m_super);
+	percpu_down_read(&mp->m_trans_rwsem);
+}
+
+static inline void
+xfs_trans_end(
+	struct xfs_mount	*mp)
+{
+	percpu_up_read(&mp->m_trans_rwsem);
+	sb_end_intwrite(mp->m_super);
+}
+
 struct xfs_buf	*xfs_trans_getsb(struct xfs_trans *);
 
 void		xfs_trans_brelse(xfs_trans_t *, struct xfs_buf *);
-- 
2.25.4