Re: [PATCH 11/11] xfs: create a polled function to force inode inactivation

From: Darrick J. Wong <djwong@kernel.org>

Create a polled version of xfs_inactive_force so that we can force
inactivation while holding a lock (usually the umount lock) without
tripping over the softlockup timer.  This is for callers that hold vfs
locks while calling inactivation, which is currently unmount, iunlink
processing during mount, and rw->ro remount.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/xfs/xfs_icache.c |   38 +++++++++++++++++++++++++++++++++++++-
 fs/xfs/xfs_icache.h |    1 +
 fs/xfs/xfs_mount.c  |    2 +-
 fs/xfs/xfs_mount.h  |    5 +++++
 fs/xfs/xfs_super.c  |    3 ++-
 5 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index d5f580b92e48..9db2beb4e732 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c

@@ -25,6 +25,7 @@
 #include "xfs_ialloc.h"
 
 #include <linux/iversion.h>
+#include <linux/nmi.h>

 
 /*
  * Allocate and initialise an xfs_inode.

@@ -2067,8 +2068,12 @@ xfs_inodegc_free_space(
 	struct xfs_mount	*mp,
 	struct xfs_eofblocks	*eofb)
 {
-	return xfs_inode_walk(mp, XFS_INODE_WALK_INACTIVE,
+	int			error;
+
+	error = xfs_inode_walk(mp, XFS_INODE_WALK_INACTIVE,
 			xfs_inactive_inode, eofb, XFS_ICI_INACTIVE_TAG);
+	wake_up(&mp->m_inactive_wait);
+	return error;
 }
 
 /* Try to get inode inactivation moving. */

@@ -2138,6 +2143,37 @@ xfs_inodegc_force(
 	flush_workqueue(mp->m_gc_workqueue);
 }
 
+/*
+ * Force all inode inactivation work to run immediately, and poll until the
+ * work is complete.  Callers should only use this function if they must
+ * inactivate inodes while holding VFS locks, and must be prepared to prevent
+ * or to wait for inodes that are queued for inactivation while this runs.
+ */
+void
+xfs_inodegc_force_poll(
+	struct xfs_mount	*mp)
+{
+	struct xfs_perag	*pag;
+	xfs_agnumber_t		agno;
+	bool			queued = false;
+
+	for_each_perag_tag(mp, agno, pag, XFS_ICI_INACTIVE_TAG)
+		queued |= xfs_inodegc_force_pag(pag);
+	if (!queued)
+		return;
+
+	/*
+	 * Touch the softlockup watchdog every 1/10th of a second while there
+	 * are still inactivation-tagged inodes in the filesystem.
+	 */
+	while (!wait_event_timeout(mp->m_inactive_wait,
+				   !radix_tree_tagged(&mp->m_perag_tree,
+						      XFS_ICI_INACTIVE_TAG),
+				   HZ / 10)) {
+		touch_softlockup_watchdog();
+	}
+}