[PATCH 1/4] xfs: make inode inactivation state changes atomic

[Dave Chinner <david@fromorbit.com>]

From: Dave Chinner <dchinner@redhat.com>

We need the XFS_NEED_INACTIVE flag to correspond to whether the
inode is on the inodegc queues so that we can then use this state
for lazy removal.

To do this, move the addition of the inode to the inodegc queue
under the ip->i_flags_lock so that it is atomic w.r.t. setting
the XFS_NEED_INACTIVE flag.

Then, when we remove the inode from the inodegc list to actually run
inactivation, clear the XFS_NEED_INACTIVE at the same time we are
setting XFS_INACTIVATING to indicate that inactivation is in
progress.

These changes result in all the state changes and inodegc queuing
being atomic w.r.t. each other and inode lookups via the use of the
ip->i_flags lock.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/xfs/xfs_icache.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index 06046827b5fe..425b55526386 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -1875,7 +1875,12 @@ xfs_inodegc_worker(
 	llist_for_each_entry_safe(ip, n, node, i_gclist) {
 		int	error;
 
-		xfs_iflags_set(ip, XFS_INACTIVATING);
+		/* Switch state to inactivating. */
+		spin_lock(&ip->i_flags_lock);
+		ip->i_flags |= XFS_INACTIVATING;
+		ip->i_flags &= ~XFS_NEED_INACTIVE;
+		spin_unlock(&ip->i_flags_lock);
+
 		error = xfs_inodegc_inactivate(ip);
 		if (error && !gc->error)
 			gc->error = error;
@@ -2068,9 +2073,13 @@ xfs_inodegc_queue(
 	unsigned long		queue_delay = 1;
 
 	trace_xfs_inode_set_need_inactive(ip);
+
+	/*
+	 * Put the addition of the inode to the gc list under the
+	 * ip->i_flags_lock so that the state change and list addition are
+	 * atomic w.r.t. lookup operations under the ip->i_flags_lock.
+	 */
 	spin_lock(&ip->i_flags_lock);
-	ip->i_flags |= XFS_NEED_INACTIVE;
-	spin_unlock(&ip->i_flags_lock);
 
 	cpu_nr = get_cpu();
 	gc = this_cpu_ptr(mp->m_inodegc);
@@ -2079,6 +2088,9 @@ xfs_inodegc_queue(
 	WRITE_ONCE(gc->items, items + 1);
 	shrinker_hits = READ_ONCE(gc->shrinker_hits);
 
+	ip->i_flags |= XFS_NEED_INACTIVE;
+	spin_unlock(&ip->i_flags_lock);
+
 	/*
 	 * Ensure the list add is always seen by anyone who finds the cpumask
 	 * bit set. This effectively gives the cpumask bit set operation
-- 
2.43.0