gfs2: Remove support for glock holder auto-demotion

Remove the support for glock holder auto-demotion (commit dc73290
and folow-ups) as we are not planning to use this feature, and the
additional code therefore only adds unnecessary complexity.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

Author: Andreas Gruenbacher

fs/gfs2/glock.c

@@ -206,12 +206,6 @@ static int demote_ok(const struct gfs2_glock *gl)
 
 	if (gl->gl_state == LM_ST_UNLOCKED)
 		return 0;
-	/*
-	 * Note that demote_ok is used for the lru process of disposing of
-	 * glocks. For this purpose, we don't care if the glock's holders
-	 * have the HIF_MAY_DEMOTE flag set or not. If someone is using
-	 * them, don't demote.
-	 */
 	if (!list_empty(&gl->gl_holders))
 		return 0;
 	if (glops->go_demote_ok)
@@ -394,7 +388,7 @@ static void do_error(struct gfs2_glock *gl, const int ret)
 	struct gfs2_holder *gh, *tmp;
 
 	list_for_each_entry_safe(gh, tmp, &gl->gl_holders, gh_list) {
-		if (!test_bit(HIF_WAIT, &gh->gh_iflags))
+		if (test_bit(HIF_HOLDER, &gh->gh_iflags))
 			continue;
 		if (ret & LM_OUT_ERROR)
 			gh->gh_error = -EIO;
@@ -408,45 +402,6 @@ static void do_error(struct gfs2_glock *gl, const int ret)
 	}
 }
 
-/**
- * demote_incompat_holders - demote incompatible demoteable holders
- * @gl: the glock we want to promote
- * @current_gh: the newly promoted holder
- *
- * We're passing the newly promoted holder in @current_gh, but actually, any of
- * the strong holders would do.
- */
-static void demote_incompat_holders(struct gfs2_glock *gl,
-				    struct gfs2_holder *current_gh)
-{
-	struct gfs2_holder *gh, *tmp;
-
-	/*
-	 * Demote incompatible holders before we make ourselves eligible.
-	 * (This holder may or may not allow auto-demoting, but we don't want
-	 * to demote the new holder before it's even granted.)
-	 */
-	list_for_each_entry_safe(gh, tmp, &gl->gl_holders, gh_list) {
-		/*
-		 * Since holders are at the front of the list, we stop when we
-		 * find the first non-holder.
-		 */
-		if (!test_bit(HIF_HOLDER, &gh->gh_iflags))
-			return;
-		if (gh == current_gh)
-			continue;
-		if (test_bit(HIF_MAY_DEMOTE, &gh->gh_iflags) &&
-		    !may_grant(gl, current_gh, gh)) {
-			/*
-			 * We should not recurse into do_promote because
-			 * __gfs2_glock_dq only calls handle_callback,
-			 * gfs2_glock_add_to_lru and __gfs2_glock_queue_work.
-			 */
-			__gfs2_glock_dq(gh);
-		}
-	}
-}
-
 /**
  * find_first_holder - find the first "holder" gh
  * @gl: the glock
@@ -465,26 +420,6 @@ static inline struct gfs2_holder *find_first_holder(const struct gfs2_glock *gl)
 	return NULL;
 }
 
-/**
- * find_first_strong_holder - find the first non-demoteable holder
- * @gl: the glock
- *
- * Find the first holder that doesn't have the HIF_MAY_DEMOTE flag set.
- */
-static inline struct gfs2_holder *
-find_first_strong_holder(struct gfs2_glock *gl)
-{
-	struct gfs2_holder *gh;
-
-	list_for_each_entry(gh, &gl->gl_holders, gh_list) {
-		if (!test_bit(HIF_HOLDER, &gh->gh_iflags))
-			return NULL;
-		if (!test_bit(HIF_MAY_DEMOTE, &gh->gh_iflags))
-			return gh;
-	}
-	return NULL;
-}
-
 /*
  * gfs2_instantiate - Call the glops instantiate function
  * @gh: The glock holder
@@ -541,9 +476,8 @@ int gfs2_instantiate(struct gfs2_holder *gh)
 static int do_promote(struct gfs2_glock *gl)
 {
 	struct gfs2_holder *gh, *current_gh;
-	bool incompat_holders_demoted = false;
 
-	current_gh = find_first_strong_holder(gl);
+	current_gh = find_first_holder(gl);
 	list_for_each_entry(gh, &gl->gl_holders, gh_list) {
 		if (test_bit(HIF_HOLDER, &gh->gh_iflags))
 			continue;
@@ -562,11 +496,8 @@ static int do_promote(struct gfs2_glock *gl)
 		set_bit(HIF_HOLDER, &gh->gh_iflags);
 		trace_gfs2_promote(gh);
 		gfs2_holder_wake(gh);
-		if (!incompat_holders_demoted) {
+		if (!current_gh)
 			current_gh = gh;
-			demote_incompat_holders(gl, current_gh);
-			incompat_holders_demoted = true;
-		}
 	}
 	return 0;
 }
@@ -1538,7 +1469,7 @@ __acquires(&gl->gl_lockref.lock)
 		if (test_bit(GLF_LOCK, &gl->gl_flags)) {
 			struct gfs2_holder *current_gh;
 
-			current_gh = find_first_strong_holder(gl);
+			current_gh = find_first_holder(gl);
 			try_futile = !may_grant(gl, current_gh, gh);
 		}
 		if (test_bit(GLF_INVALIDATE_IN_PROGRESS, &gl->gl_flags))
@@ -1550,8 +1481,6 @@ __acquires(&gl->gl_lockref.lock)
 			continue;
 		if (gh->gh_gl->gl_ops->go_type == LM_TYPE_FLOCK)
 			continue;
-		if (test_bit(HIF_MAY_DEMOTE, &gh2->gh_iflags))
-			continue;
 		if (!pid_is_meaningful(gh2))
 			continue;
 		goto trap_recursive;
@@ -1666,64 +1595,42 @@ static void __gfs2_glock_dq(struct gfs2_holder *gh)
 	int fast_path = 0;
 
 	/*
-	 * This while loop is similar to function demote_incompat_holders:
-	 * If the glock is due to be demoted (which may be from another node
-	 * or even if this holder is GL_NOCACHE), the weak holders are
-	 * demoted as well, allowing the glock to be demoted.
+	 * If we're in the process of file system withdraw, we cannot just
+	 * dequeue any glocks until our journal is recovered, lest we introduce
+	 * file system corruption. We need two exceptions to this rule: We need
+	 * to allow unlocking of nondisk glocks and the glock for our own
+	 * journal that needs recovery.
 	 */
-	while (gh) {
-		/*
-		 * If we're in the process of file system withdraw, we cannot
-		 * just dequeue any glocks until our journal is recovered, lest
-		 * we introduce file system corruption. We need two exceptions
-		 * to this rule: We need to allow unlocking of nondisk glocks
-		 * and the glock for our own journal that needs recovery.
-		 */
-		if (test_bit(SDF_WITHDRAW_RECOVERY, &sdp->sd_flags) &&
-		    glock_blocked_by_withdraw(gl) &&
-		    gh->gh_gl != sdp->sd_jinode_gl) {
-			sdp->sd_glock_dqs_held++;
-			spin_unlock(&gl->gl_lockref.lock);
-			might_sleep();
-			wait_on_bit(&sdp->sd_flags, SDF_WITHDRAW_RECOVERY,
-				    TASK_UNINTERRUPTIBLE);
-			spin_lock(&gl->gl_lockref.lock);
-		}
+	if (test_bit(SDF_WITHDRAW_RECOVERY, &sdp->sd_flags) &&
+	    glock_blocked_by_withdraw(gl) &&
+	    gh->gh_gl != sdp->sd_jinode_gl) {
+		sdp->sd_glock_dqs_held++;
+		spin_unlock(&gl->gl_lockref.lock);
+		might_sleep();
+		wait_on_bit(&sdp->sd_flags, SDF_WITHDRAW_RECOVERY,
+			    TASK_UNINTERRUPTIBLE);
+		spin_lock(&gl->gl_lockref.lock);
+	}
 
-		/*
-		 * This holder should not be cached, so mark it for demote.
-		 * Note: this should be done before the check for needs_demote
-		 * below.
-		 */
-		if (gh->gh_flags & GL_NOCACHE)
-			handle_callback(gl, LM_ST_UNLOCKED, 0, false);
+	/*
+	 * This holder should not be cached, so mark it for demote.
+	 * Note: this should be done before the check for needs_demote
+	 * below.
+	 */
+	if (gh->gh_flags & GL_NOCACHE)
+		handle_callback(gl, LM_ST_UNLOCKED, 0, false);
 
-		list_del_init(&gh->gh_list);
-		clear_bit(HIF_HOLDER, &gh->gh_iflags);
-		trace_gfs2_glock_queue(gh, 0);
+	list_del_init(&gh->gh_list);
+	clear_bit(HIF_HOLDER, &gh->gh_iflags);
+	trace_gfs2_glock_queue(gh, 0);
 
-		/*
-		 * If there hasn't been a demote request we are done.
-		 * (Let the remaining holders, if any, keep holding it.)
-		 */
-		if (!needs_demote(gl)) {
-			if (list_empty(&gl->gl_holders))
-				fast_path = 1;
-			break;
-		}
-		/*
-		 * If we have another strong holder (we cannot auto-demote)
-		 * we are done. It keeps holding it until it is done.
-		 */
-		if (find_first_strong_holder(gl))
-			break;
-
-		/*
-		 * If we have a weak holder at the head of the list, it
-		 * (and all others like it) must be auto-demoted. If there
-		 * are no more weak holders, we exit the while loop.
-		 */
-		gh = find_first_holder(gl);
+	/*
+	 * If there hasn't been a demote request we are done.
+	 * (Let the remaining holders, if any, keep holding it.)
+	 */
+	if (!needs_demote(gl)) {
+		if (list_empty(&gl->gl_holders))
+			fast_path = 1;
 	}
 
 	if (!test_bit(GLF_LFLUSH, &gl->gl_flags) && demote_ok(gl))
@@ -1938,33 +1845,6 @@ void gfs2_glock_cb(struct gfs2_glock *gl, unsigned int state)
 		if (test_bit(GLF_REPLY_PENDING, &gl->gl_flags))
 			delay = gl->gl_hold_time;
 	}
-	/*
-	 * Note 1: We cannot call demote_incompat_holders from handle_callback
-	 * or gfs2_set_demote due to recursion problems like: gfs2_glock_dq ->
-	 * handle_callback -> demote_incompat_holders -> gfs2_glock_dq
-	 * Plus, we only want to demote the holders if the request comes from
-	 * a remote cluster node because local holder conflicts are resolved
-	 * elsewhere.
-	 *
-	 * Note 2: if a remote node wants this glock in EX mode, lock_dlm will
-	 * request that we set our state to UNLOCKED. Here we mock up a holder
-	 * to make it look like someone wants the lock EX locally. Any SH
-	 * and DF requests should be able to share the lock without demoting.
-	 *
-	 * Note 3: We only want to demote the demoteable holders when there
-	 * are no more strong holders. The demoteable holders might as well
-	 * keep the glock until the last strong holder is done with it.
-	 */
-	if (!find_first_strong_holder(gl)) {
-		struct gfs2_holder mock_gh = {
-			.gh_gl = gl,
-			.gh_state = (state == LM_ST_UNLOCKED) ?
-				    LM_ST_EXCLUSIVE : state,
-			.gh_iflags = BIT(HIF_HOLDER)
-		};
-
-		demote_incompat_holders(gl, &mock_gh);
-	}
 	handle_callback(gl, state, delay, true);
 	__gfs2_glock_queue_work(gl, delay);
 	spin_unlock(&gl->gl_lockref.lock);
@@ -2356,8 +2236,6 @@ static const char *hflags2str(char *buf, u16 flags, unsigned long iflags)
 		*p++ = 'H';
 	if (test_bit(HIF_WAIT, &iflags))
 		*p++ = 'W';
-	if (test_bit(HIF_MAY_DEMOTE, &iflags))
-		*p++ = 'D';
 	if (flags & GL_SKIP)
 		*p++ = 's';
 	*p = 0;

fs/gfs2/glock.h

@@ -156,8 +156,6 @@ static inline struct gfs2_holder *gfs2_glock_is_locked_by_me(struct gfs2_glock *
 	list_for_each_entry(gh, &gl->gl_holders, gh_list) {
 		if (!test_bit(HIF_HOLDER, &gh->gh_iflags))
 			break;
-		if (test_bit(HIF_MAY_DEMOTE, &gh->gh_iflags))
-			continue;
 		if (gh->gh_owner_pid == pid)
 			goto out;
 	}
@@ -308,24 +306,6 @@ static inline bool gfs2_holder_queued(struct gfs2_holder *gh)
 	return !list_empty(&gh->gh_list);
 }
 
-static inline void gfs2_holder_allow_demote(struct gfs2_holder *gh)
-{
-	struct gfs2_glock *gl = gh->gh_gl;
-
-	spin_lock(&gl->gl_lockref.lock);
-	set_bit(HIF_MAY_DEMOTE, &gh->gh_iflags);
-	spin_unlock(&gl->gl_lockref.lock);
-}
-
-static inline void gfs2_holder_disallow_demote(struct gfs2_holder *gh)
-{
-	struct gfs2_glock *gl = gh->gh_gl;
-
-	spin_lock(&gl->gl_lockref.lock);
-	clear_bit(HIF_MAY_DEMOTE, &gh->gh_iflags);
-	spin_unlock(&gl->gl_lockref.lock);
-}
-
 extern void gfs2_inode_remember_delete(struct gfs2_glock *gl, u64 generation);
 extern bool gfs2_inode_already_deleted(struct gfs2_glock *gl, u64 generation);
 

fs/gfs2/incore.h

@@ -252,7 +252,6 @@ struct gfs2_lkstats {
 
 enum {
 	/* States */
-	HIF_MAY_DEMOTE		= 1,
 	HIF_HOLDER		= 6,  /* Set for gh that "holds" the glock */
 	HIF_WAIT		= 10,
 };