xfs: create traced helper to get extra perag references

There are a few places in the XFS codebase where a caller has either an
active or a passive reference to a perag structure and wants to give
a passive reference to some other piece of code.  Btree cursor creation
and inode walks are good examples of this.  Replace the open-coded logic
with a helper to do this.

The new function adds a few safeguards -- it checks that there's at
least one reference to the perag structure passed in, and it records the
refcount bump in the ftrace information.  This makes it much easier to
debug perag refcounting problems.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

6 files changed, 18 insertions, 14 deletions

diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
index ae45f546ed86..2d8910046ed9 100644
--- a/fs/xfs/libxfs/xfs_ag.c
+++ b/fs/xfs/libxfs/xfs_ag.c
@@ -81,6 +81,19 @@ xfs_perag_get_tag(
 	return pag;
 }
 
+/* Get a passive reference to the given perag. */
+struct xfs_perag *
+xfs_perag_hold(
+	struct xfs_perag	*pag)
+{
+	ASSERT(atomic_read(&pag->pag_ref) > 0 ||
+	       atomic_read(&pag->pag_active_ref) > 0);
+
+	trace_xfs_perag_hold(pag, _RET_IP_);
+	atomic_inc(&pag->pag_ref);
+	return pag;
+}
+
 void
 xfs_perag_put(
 	struct xfs_perag	*pag)
diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
index 5e18536dfdce..8092eaba977d 100644
--- a/fs/xfs/libxfs/xfs_ag.h
+++ b/fs/xfs/libxfs/xfs_ag.h
@@ -134,6 +134,7 @@ void xfs_free_perag(struct xfs_mount *mp);
 struct xfs_perag *xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno);
 struct xfs_perag *xfs_perag_get_tag(struct xfs_mount *mp, xfs_agnumber_t agno,
 		unsigned int tag);
+struct xfs_perag *xfs_perag_hold(struct xfs_perag *pag);
 void xfs_perag_put(struct xfs_perag *pag);
 
 /* Active AG references */
diff --git a/fs/xfs/libxfs/xfs_alloc_btree.c b/fs/xfs/libxfs/xfs_alloc_btree.c
index 0f29c7b1b39f..8e8416c14cec 100644
--- a/fs/xfs/libxfs/xfs_alloc_btree.c
+++ b/fs/xfs/libxfs/xfs_alloc_btree.c
@@ -492,9 +492,7 @@ xfs_allocbt_init_common(
 		cur->bc_statoff = XFS_STATS_CALC_INDEX(xs_abtb_2);
 	}
 
-	/* take a reference for the cursor */
-	atomic_inc(&pag->pag_ref);
-	cur->bc_ag.pag = pag;
+	cur->bc_ag.pag = xfs_perag_hold(pag);
 
 	if (xfs_has_crc(mp))
 		cur->bc_flags |= XFS_BTREE_CRC_BLOCKS;
diff --git a/fs/xfs/libxfs/xfs_ialloc_btree.c b/fs/xfs/libxfs/xfs_ialloc_btree.c
index 1d2af50ac95b..ad6c521f05eb 100644
--- a/fs/xfs/libxfs/xfs_ialloc_btree.c
+++ b/fs/xfs/libxfs/xfs_ialloc_btree.c
@@ -450,9 +450,7 @@ xfs_inobt_init_common(
 	if (xfs_has_crc(mp))
 		cur->bc_flags |= XFS_BTREE_CRC_BLOCKS;
 
-	/* take a reference for the cursor */
-	atomic_inc(&pag->pag_ref);
-	cur->bc_ag.pag = pag;
+	cur->bc_ag.pag = xfs_perag_hold(pag);
 	return cur;
 }
 
diff --git a/fs/xfs/libxfs/xfs_refcount_btree.c b/fs/xfs/libxfs/xfs_refcount_btree.c
index 749e837de98d..03d2b01487a1 100644
--- a/fs/xfs/libxfs/xfs_refcount_btree.c
+++ b/fs/xfs/libxfs/xfs_refcount_btree.c
@@ -340,10 +340,7 @@ xfs_refcountbt_init_common(
 
 	cur->bc_flags |= XFS_BTREE_CRC_BLOCKS;
 
-	/* take a reference for the cursor */
-	atomic_inc(&pag->pag_ref);
-	cur->bc_ag.pag = pag;
-
+	cur->bc_ag.pag = xfs_perag_hold(pag);
 	cur->bc_ag.refc.nr_ops = 0;
 	cur->bc_ag.refc.shape_changes = 0;
 	cur->bc_ops = &xfs_refcountbt_ops;
diff --git a/fs/xfs/libxfs/xfs_rmap_btree.c b/fs/xfs/libxfs/xfs_rmap_btree.c
index d3285684bb5e..56d074b42660 100644
--- a/fs/xfs/libxfs/xfs_rmap_btree.c
+++ b/fs/xfs/libxfs/xfs_rmap_btree.c
@@ -460,10 +460,7 @@ xfs_rmapbt_init_common(
 	cur->bc_statoff = XFS_STATS_CALC_INDEX(xs_rmap_2);
 	cur->bc_ops = &xfs_rmapbt_ops;
 
-	/* take a reference for the cursor */
-	atomic_inc(&pag->pag_ref);
-	cur->bc_ag.pag = pag;
-
+	cur->bc_ag.pag = xfs_perag_hold(pag);
 	return cur;
 }