[Cluster-devel] [PATCH v3 09/20] gfs2: Get rid of sd_reserving_log

[Andreas Gruenbacher]

This counter and the associated wait queue are only used so that
gfs2_make_fs_ro can efficiently wait for all pending log space
allocations to fail after setting the filesystem to read-only.  This
comes at the cost of waking up that wait queue very frequently.

Instead, when gfs2_log_reserve fails because the filesystem has become
read-only, Wake up sd_log_waitq.  In gfs2_make_fs_ro, set the file
system read-only and then wait until all the log space has been
released.  Give up and report the problem after a while.  With that,
sd_reserving_log and sd_reserving_log_wait can be removed.

Signed-off-by: Andreas Gruenbacher <agruenba at redhat.com>
---
 fs/gfs2/incore.h     |  3 ---
 fs/gfs2/log.c        | 17 ++++++++++-------
 fs/gfs2/log.h        |  1 +
 fs/gfs2/ops_fstype.c |  2 --
 fs/gfs2/super.c      | 12 ++++++------
 fs/gfs2/trans.c      |  5 ++++-
 6 files changed, 21 insertions(+), 19 deletions(-)

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 958810e533ad..c155fd39bc98 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -848,9 +848,6 @@ struct gfs2_sbd {
 	int sd_log_error; /* First log error */
 	wait_queue_head_t sd_withdraw_wait;
 
-	atomic_t sd_reserving_log;
-	wait_queue_head_t sd_reserving_log_wait;
-
 	unsigned int sd_log_flush_head;
 
 	spinlock_t sd_ail_lock;
diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 721d2d7f0efd..2e84ba153cdf 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -397,6 +397,15 @@ static void ail2_empty(struct gfs2_sbd *sdp, unsigned int new_tail)
 	spin_unlock(&sdp->sd_ail_lock);
 }
 
+/**
+ * gfs2_log_is_empty - Check if the log is empty
+ * @sdp: The GFS2 superblock
+ */
+
+bool gfs2_log_is_empty(struct gfs2_sbd *sdp) {
+	return atomic_read(&sdp->sd_log_blks_free) == sdp->sd_jdesc->jd_blocks;
+}
+
 /**
  * gfs2_log_release - Release a given number of log blocks
  * @sdp: The GFS2 superblock
@@ -461,13 +470,9 @@ int gfs2_log_reserve(struct gfs2_sbd *sdp, unsigned int blks)
 		} while(free_blocks <= wanted);
 		finish_wait(&sdp->sd_log_waitq, &wait);
 	}
-	atomic_inc(&sdp->sd_reserving_log);
 	if (atomic_cmpxchg(&sdp->sd_log_blks_free, free_blocks,
-				free_blocks - blks) != free_blocks) {
-		if (atomic_dec_and_test(&sdp->sd_reserving_log))
-			wake_up(&sdp->sd_reserving_log_wait);
+				free_blocks - blks) != free_blocks)
 		goto retry;
-	}
 	atomic_sub(blks, &sdp->sd_log_blks_needed);
 	trace_gfs2_log_blocks(sdp, -blks);
 
@@ -483,8 +488,6 @@ int gfs2_log_reserve(struct gfs2_sbd *sdp, unsigned int blks)
 		gfs2_log_release(sdp, blks);
 		ret = -EROFS;
 	}
-	if (atomic_dec_and_test(&sdp->sd_reserving_log))
-		wake_up(&sdp->sd_reserving_log_wait);
 	return ret;
 }
 
diff --git a/fs/gfs2/log.h b/fs/gfs2/log.h
index a9cdbc990edf..16efbe614279 100644
--- a/fs/gfs2/log.h
+++ b/fs/gfs2/log.h
@@ -64,6 +64,7 @@ static inline void gfs2_ordered_add_inode(struct gfs2_inode *ip)
 extern void gfs2_ordered_del_inode(struct gfs2_inode *ip);
 extern unsigned int gfs2_struct2blk(struct gfs2_sbd *sdp, unsigned int nstruct);
 extern void gfs2_remove_from_ail(struct gfs2_bufdata *bd);
+extern bool gfs2_log_is_empty(struct gfs2_sbd *sdp);
 extern void gfs2_log_release(struct gfs2_sbd *sdp, unsigned int blks);
 extern int gfs2_log_reserve(struct gfs2_sbd *sdp, unsigned int blks);
 extern void gfs2_write_log_header(struct gfs2_sbd *sdp, struct gfs2_jdesc *jd,
diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 61fce59cb4d3..986dc2ebebf0 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -136,8 +136,6 @@ static struct gfs2_sbd *init_sbd(struct super_block *sb)
 
 	init_rwsem(&sdp->sd_log_flush_lock);
 	atomic_set(&sdp->sd_log_in_flight, 0);
-	atomic_set(&sdp->sd_reserving_log, 0);
-	init_waitqueue_head(&sdp->sd_reserving_log_wait);
 	init_waitqueue_head(&sdp->sd_log_flush_wait);
 	atomic_set(&sdp->sd_freeze_state, SFS_UNFROZEN);
 	mutex_init(&sdp->sd_freeze_mutex);
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index ed7a829e9ffe..f188277f7d48 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -645,13 +645,13 @@ int gfs2_make_fs_ro(struct gfs2_sbd *sdp)
 
 		gfs2_log_flush(sdp, NULL, GFS2_LOG_HEAD_FLUSH_SHUTDOWN |
 			       GFS2_LFC_MAKE_FS_RO);
-		wait_event(sdp->sd_reserving_log_wait,
-			   atomic_read(&sdp->sd_reserving_log) == 0);
-		gfs2_assert_warn(sdp, atomic_read(&sdp->sd_log_blks_free) ==
-				 sdp->sd_jdesc->jd_blocks);
+		wait_event_timeout(sdp->sd_log_waitq,
+				   gfs2_log_is_empty(sdp),
+				   HZ * 5);
+		gfs2_assert_warn(sdp, gfs2_log_is_empty(sdp));
 	} else {
-		wait_event_timeout(sdp->sd_reserving_log_wait,
-				   atomic_read(&sdp->sd_reserving_log) == 0,
+		wait_event_timeout(sdp->sd_log_waitq,
+				   gfs2_log_is_empty(sdp),
 				   HZ * 5);
 	}
 	if (gfs2_holder_initialized(&freeze_gh))
diff --git a/fs/gfs2/trans.c b/fs/gfs2/trans.c
index 4f461ab37ced..e33cb8da056a 100644
--- a/fs/gfs2/trans.c
+++ b/fs/gfs2/trans.c
@@ -73,8 +73,11 @@ int __gfs2_trans_begin(struct gfs2_sbd *sdp, unsigned int blocks,
 	sb_start_intwrite(sdp->sd_vfs);
 
 	error = gfs2_log_reserve(sdp, tr->tr_reserved);
-	if (error)
+	if (error) {
+		if (error == -EROFS)
+			wake_up(&sdp->sd_log_waitq);
 		goto fail;
+	}
 
 	current->journal_info = tr;
 
-- 
2.26.2