[PATCH 6/6] [XFS] Reference count per-ag structures

[Dave Chinner <david@fromorbit.com>]

Reference count the per-ag structures to ensure that we keep get/put
pairs balanced. Assert that the reference counts are zero at unmount
time to catch leaks. In future, reference counts will enable us to
safely remove perag structures by allowing us to detect when they
are no longer in use.

Signed-off-by: Dave Chinner <david@fromorbit.com>
---
 fs/xfs/xfs_ag.h    |    4 ++--
 fs/xfs/xfs_alloc.c |    2 +-
 fs/xfs/xfs_inode.c |    5 ++++-
 fs/xfs/xfs_mount.c |    1 +
 fs/xfs/xfs_mount.h |   11 +++++++++--
 5 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/xfs_ag.h b/fs/xfs/xfs_ag.h
index a5d54bf..b384a3c 100644
--- a/fs/xfs/xfs_ag.h
+++ b/fs/xfs/xfs_ag.h
@@ -182,8 +182,8 @@ typedef struct xfs_perag_busy {
 #define XFS_PAGB_NUM_SLOTS	128
 #endif
 
-typedef struct xfs_perag
-{
+typedef struct xfs_perag {
+	atomic_t	pag_ref;	/* perag reference count */
 	char		pagf_init;	/* this agf's entry is initialized */
 	char		pagi_init;	/* this agi's entry is initialized */
 	char		pagf_metadata;	/* the agf is preferred to be metadata */
diff --git a/fs/xfs/xfs_alloc.c b/fs/xfs/xfs_alloc.c
index 2d076e2..d1349b1 100644
--- a/fs/xfs/xfs_alloc.c
+++ b/fs/xfs/xfs_alloc.c
@@ -2545,7 +2545,6 @@ xfs_alloc_vextent(
 			}
 			xfs_perag_put(args->pag);
 		}
-		xfs_perag_put(args->pag);
 		if (bump_rotor || (type == XFS_ALLOCTYPE_ANY_AG)) {
 			if (args->agno == sagno)
 				mp->m_agfrotor = (mp->m_agfrotor + 1) %
@@ -2571,6 +2570,7 @@ xfs_alloc_vextent(
 			args->len);
 #endif
 	}
+	xfs_perag_put(args->pag);
 	return 0;
 error0:
 	xfs_perag_put(args->pag);
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 44a1168..e6c178e 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -2729,7 +2729,7 @@ xfs_iflush_cluster(
 	ilist_size = inodes_per_cluster * sizeof(xfs_inode_t *);
 	ilist = kmem_alloc(ilist_size, KM_MAYFAIL|KM_NOFS);
 	if (!ilist)
-		return 0;
+		goto out_put;
 
 	mask = ~(((XFS_INODE_CLUSTER_SIZE(mp) >> mp->m_sb.sb_inodelog)) - 1);
 	first_index = XFS_INO_TO_AGINO(mp, ip->i_ino) & mask;
@@ -2798,6 +2798,8 @@ xfs_iflush_cluster(
 out_free:
 	read_unlock(&pag->pag_ici_lock);
 	kmem_free(ilist);
+out_put:
+	xfs_perag_put(pag);
 	return 0;
 
 
@@ -2841,6 +2843,7 @@ cluster_corrupt_out:
 	 */
 	xfs_iflush_abort(iq);
 	kmem_free(ilist);
+	xfs_perag_put(pag);
 	return XFS_ERROR(EFSCORRUPTED);
 }
 
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index d6de63d..21f1b29 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -213,6 +213,7 @@ xfs_free_perag(
 	for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
 		spin_lock(&mp->m_perag_lock);
 		pag = radix_tree_delete(&mp->m_perag_tree, agno);
+		ASSERT(atomic_read(&pag->pag_ref) == 0);
 		spin_unlock(&mp->m_perag_lock);
 		if (!pag)
 			continue;
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index b2aa726..225eb29 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -384,7 +384,7 @@ xfs_daddr_to_agbno(struct xfs_mount *mp, xfs_daddr_t d)
 }
 
 /*
- * perag get/put wrappers for eventual ref counting
+ * perag get/put wrappers for ref counting
  */
 static inline xfs_perag_t *
 xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno)
@@ -393,6 +393,12 @@ xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno)
 
 	spin_lock(&mp->m_perag_lock);
 	pag = radix_tree_lookup(&mp->m_perag_tree, agno);
+	if (pag) {
+		ASSERT(atomic_read(&pag->pag_ref) >= 0);
+		/* catch leaks in the positive direction during testing */
+		ASSERT(atomic_read(&pag->pag_ref) < 1000);
+		atomic_inc(&pag->pag_ref);
+	}
 	spin_unlock(&mp->m_perag_lock);
 	return pag;
 }
@@ -400,7 +406,8 @@ xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno)
 static inline void
 xfs_perag_put(xfs_perag_t *pag)
 {
-	/* nothing to see here, move along */
+	ASSERT(atomic_read(&pag->pag_ref) > 0);
+	atomic_dec(&pag->pag_ref);
 }
 
 /*
-- 
1.6.5

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