GFS2: update freeze code to use freeze/thaw_super on all nodes

The current gfs2 freezing code is considerably more complicated than it
should be because it doesn't use the vfs freezing code on any node except
the one that begins the freeze.  This is because it needs to acquire a
cluster glock before calling the vfs code to prevent a deadlock, and
without the new freeze_super and thaw_super hooks, that was impossible. To
deal with the issue, gfs2 had to do some hacky locking tricks to make sure
that a frozen node couldn't be holding on a lock it needed to do the
unfreeze ioctl.

This patch makes use of the new hooks to simply the gfs2 locking code. Now,
all the nodes in the cluster freeze and thaw in exactly the same way. Every
node in the cluster caches the freeze glock in the shared state.  The new
freeze_super hook allows the freezing node to grab this freeze glock in
the exclusive state without first calling the vfs freeze_super function.
All the nodes in the cluster see this lock change, and call the vfs
freeze_super function. The vfs locking code guarantees that the nodes can't
get stuck holding the glocks necessary to unfreeze the system.  To
unfreeze, the freezing node uses the new thaw_super hook to drop the freeze
glock. Again, all the nodes notice this, reacquire the glock in shared mode
and call the vfs thaw_super function.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 12 insertions, 14 deletions

diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
index 1cc0bba6313f..fe91951c3361 100644
--- a/fs/gfs2/glops.c
+++ b/fs/gfs2/glops.c
@@ -28,6 +28,8 @@
 #include "trans.h"
 #include "dir.h"
 
+struct workqueue_struct *gfs2_freeze_wq;
+
 static void gfs2_ail_error(struct gfs2_glock *gl, const struct buffer_head *bh)
 {
 	fs_err(gl->gl_sbd, "AIL buffer %p: blocknr %llu state 0x%08lx mapping %p page state 0x%lx\n",
@@ -94,11 +96,8 @@ static void gfs2_ail_empty_gl(struct gfs2_glock *gl)
          * on the stack */
 	tr.tr_reserved = 1 + gfs2_struct2blk(sdp, tr.tr_revokes, sizeof(u64));
 	tr.tr_ip = _RET_IP_;
-	sb_start_intwrite(sdp->sd_vfs);
-	if (gfs2_log_reserve(sdp, tr.tr_reserved) < 0) {
-		sb_end_intwrite(sdp->sd_vfs);
+	if (gfs2_log_reserve(sdp, tr.tr_reserved) < 0)
 		return;
-	}
 	WARN_ON_ONCE(current->journal_info);
 	current->journal_info = &tr;
 
@@ -469,20 +468,19 @@ static void inode_go_dump(struct seq_file *seq, const struct gfs2_glock *gl)
 
 static void freeze_go_sync(struct gfs2_glock *gl)
 {
+	int error = 0;
 	struct gfs2_sbd *sdp = gl->gl_sbd;
-	DEFINE_WAIT(wait);
 
 	if (gl->gl_state == LM_ST_SHARED &&
 	    test_bit(SDF_JOURNAL_LIVE, &sdp->sd_flags)) {
-		atomic_set(&sdp->sd_log_freeze, 1);
-		wake_up(&sdp->sd_logd_waitq);
-		do {
-			prepare_to_wait(&sdp->sd_log_frozen_wait, &wait,
-					TASK_UNINTERRUPTIBLE);
-			if (atomic_read(&sdp->sd_log_freeze))
-				io_schedule();
-		} while(atomic_read(&sdp->sd_log_freeze));
-		finish_wait(&sdp->sd_log_frozen_wait, &wait);
+		atomic_set(&sdp->sd_freeze_state, SFS_STARTING_FREEZE);
+		error = freeze_super(sdp->sd_vfs);
+		if (error) {
+			printk(KERN_INFO "GFS2: couldn't freeze filesystem: %d\n", error);
+			gfs2_assert_withdraw(sdp, 0);
+		}
+		queue_work(gfs2_freeze_wq, &sdp->sd_freeze_work);
+		gfs2_log_flush(sdp, NULL, FREEZE_FLUSH);
 	}
 }