gfs2: Get rid of demote_ok checks

JIRA: https://issues.redhat.com/browse/RHEL-67675

The demote_ok glock operation is only still used to prevent the inode
glocks of the "jindex" and "rindex" directories from getting recycled
while they are still referenced by sdp->sd_jindex and sdp->sd_rindex.
However, the LRU walking code will no longer recycle glocks which are
referenced, so the demote_ok glock operation is obsolete and can be
removed.

Each of a glock's holders in the gl_holders list is holding a reference
on the glock, so when the list of holders isn't empty in demote_ok(),
the existing reference count check will already prevent the glock from
getting released.  This means that demote_ok() is obsolete as well.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
(cherry picked from commit 713f883)

Author: Andreas Gruenbacher

Documentation/filesystems/gfs2-glocks.rst

@@ -62,8 +62,6 @@ Field              Purpose
 go_sync            Called before remote state change (e.g. to sync dirty data)
 go_xmote_bh        Called after remote state change (e.g. to refill cache)
 go_inval           Called if remote state change requires invalidating the cache
-go_demote_ok       Returns boolean value of whether its ok to demote a glock
-                   (e.g. checks timeout, and that there is no cached data)
 go_instantiate     Called when a glock has been acquired
 go_held            Called every time a glock holder is acquired
 go_dump            Called to print content of object for debugfs file, or on
@@ -96,7 +94,6 @@ Operation        GLF_LOCK bit lock held    gl_lockref.lock spinlock held
 go_sync               Yes                       No
 go_xmote_bh           Yes                       No
 go_inval              Yes                       No
-go_demote_ok          Sometimes                 Yes
 go_instantiate        No                        No
 go_held               No                        No
 go_dump               Sometimes                 Yes

fs/gfs2/glock.c

@@ -217,27 +217,6 @@ struct gfs2_glock *gfs2_glock_hold(struct gfs2_glock *gl)
 	return gl;
 }
 
-/**
- * demote_ok - Check to see if it's ok to unlock a glock
- * @gl: the glock
- *
- * Returns: 1 if it's ok
- */
-
-static int demote_ok(const struct gfs2_glock *gl)
-{
-	const struct gfs2_glock_operations *glops = gl->gl_ops;
-
-	if (gl->gl_state == LM_ST_UNLOCKED)
-		return 0;
-	if (!list_empty(&gl->gl_holders))
-		return 0;
-	if (glops->go_demote_ok)
-		return glops->go_demote_ok(gl);
-	return 1;
-}
-
-
 static void gfs2_glock_add_to_lru(struct gfs2_glock *gl)
 {
 	spin_lock(&lru_lock);
@@ -2026,7 +2005,7 @@ __acquires(&lru_lock)
 		clear_bit(GLF_LRU, &gl->gl_flags);
 		freed++;
 		gl->gl_lockref.count++;
-		if (demote_ok(gl))
+		if (gl->gl_state != LM_ST_UNLOCKED)
 			request_demote(gl, LM_ST_UNLOCKED, 0, false);
 		gfs2_glock_queue_work(gl, 0);
 		spin_unlock(&gl->gl_lockref.lock);

fs/gfs2/glops.c

@@ -381,23 +381,6 @@ static void inode_go_inval(struct gfs2_glock *gl, int flags)
 	gfs2_clear_glop_pending(ip);
 }
 
-/**
- * inode_go_demote_ok - Check to see if it's ok to unlock an inode glock
- * @gl: the glock
- *
- * Returns: 1 if it's ok
- */
-
-static int inode_go_demote_ok(const struct gfs2_glock *gl)
-{
-	struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
-
-	if (sdp->sd_jindex == gl->gl_object || sdp->sd_rindex == gl->gl_object)
-		return 0;
-
-	return 1;
-}
-
 static int gfs2_dinode_in(struct gfs2_inode *ip, const void *buf)
 {
 	const struct gfs2_dinode *str = buf;
@@ -721,7 +704,6 @@ const struct gfs2_glock_operations gfs2_meta_glops = {
 const struct gfs2_glock_operations gfs2_inode_glops = {
 	.go_sync = inode_go_sync,
 	.go_inval = inode_go_inval,
-	.go_demote_ok = inode_go_demote_ok,
 	.go_instantiate = inode_go_instantiate,
 	.go_held = inode_go_held,
 	.go_dump = inode_go_dump,

fs/gfs2/incore.h

@@ -218,7 +218,6 @@ struct gfs2_glock_operations {
 	int (*go_sync) (struct gfs2_glock *gl);
 	int (*go_xmote_bh)(struct gfs2_glock *gl);
 	void (*go_inval) (struct gfs2_glock *gl, int flags);
-	int (*go_demote_ok) (const struct gfs2_glock *gl);
 	int (*go_instantiate) (struct gfs2_glock *gl);
 	int (*go_held)(struct gfs2_holder *gh);
 	void (*go_dump)(struct seq_file *seq, struct gfs2_glock *gl,