GFS2: Fix "truncate in progress" hang

Following on from the recent clean up of gfs2_quotad, this patch moves
the processing of "truncate in progress" inodes from the glock workqueue
into gfs2_quotad. This fixes a hang due to the "truncate in progress"
processing requiring glocks in order to complete.

It might seem odd to use gfs2_quotad for this particular item, but
we have to use a pre-existing thread since creating a thread implies
a GFP_KERNEL memory allocation which is not allowed from the glock
workqueue context. Of the existing threads, gfs2_logd and gfs2_recoverd
may deadlock if used for this operation. gfs2_scand and gfs2_glockd are
both scheduled for removal at some (hopefully not too distant) future
point. That leaves only gfs2_quotad whose workload is generally fairly
light and is easily adapted for this extra task.

Also, as a result of this change, it opens the way for a future patch to
make the reading of the inode's information asynchronous with respect to
the glock workqueue, which is another improvement that has been on the list
for some time now.

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

1 files changed, 29 insertions, 4 deletions

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 27cb9cca9c0..4ddf3bd55dd 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -40,6 +40,7 @@
 #include "quota.h"
 #include "super.h"
 #include "util.h"
+#include "bmap.h"
 
 struct gfs2_gl_hash_bucket {
         struct hlist_head hb_list;
@@ -289,7 +290,8 @@ static void gfs2_holder_wake(struct gfs2_holder *gh)
  * do_promote - promote as many requests as possible on the current queue
  * @gl: The glock
  * 
- * Returns: true if there is a blocked holder at the head of the list
+ * Returns: 1 if there is a blocked holder at the head of the list, or 2
+ *          if a type specific operation is underway.
  */
 
 static int do_promote(struct gfs2_glock *gl)
@@ -312,6 +314,8 @@ restart:
 				ret = glops->go_lock(gh);
 				spin_lock(&gl->gl_spin);
 				if (ret) {
+					if (ret == 1)
+						return 2;
 					gh->gh_error = ret;
 					list_del_init(&gh->gh_list);
 					gfs2_holder_wake(gh);
@@ -416,6 +420,7 @@ static void finish_xmote(struct gfs2_glock *gl, unsigned int ret)
 	const struct gfs2_glock_operations *glops = gl->gl_ops;
 	struct gfs2_holder *gh;
 	unsigned state = ret & LM_OUT_ST_MASK;
+	int rv;
 
 	spin_lock(&gl->gl_spin);
 	state_change(gl, state);
@@ -470,7 +475,6 @@ retry:
 		gfs2_demote_wake(gl);
 	if (state != LM_ST_UNLOCKED) {
 		if (glops->go_xmote_bh) {
-			int rv;
 			spin_unlock(&gl->gl_spin);
 			rv = glops->go_xmote_bh(gl, gh);
 			if (rv == -EAGAIN)
@@ -481,10 +485,13 @@ retry:
 				goto out;
 			}
 		}
-		do_promote(gl);
+		rv = do_promote(gl);
+		if (rv == 2)
+			goto out_locked;
 	}
 out:
 	clear_bit(GLF_LOCK, &gl->gl_flags);
+out_locked:
 	spin_unlock(&gl->gl_spin);
 	gfs2_glock_put(gl);
 }
@@ -584,6 +591,7 @@ __releases(&gl->gl_spin)
 __acquires(&gl->gl_spin)
 {
 	struct gfs2_holder *gh = NULL;
+	int ret;
 
 	if (test_and_set_bit(GLF_LOCK, &gl->gl_flags))
 		return;
@@ -602,8 +610,11 @@ __acquires(&gl->gl_spin)
 	} else {
 		if (test_bit(GLF_DEMOTE, &gl->gl_flags))
 			gfs2_demote_wake(gl);
-		if (do_promote(gl) == 0)
+		ret = do_promote(gl);
+		if (ret == 0)
 			goto out;
+		if (ret == 2)
+			return;
 		gh = find_first_waiter(gl);
 		gl->gl_target = gh->gh_state;
 		if (!(gh->gh_flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB)))
@@ -1556,6 +1567,20 @@ void gfs2_gl_hash_clear(struct gfs2_sbd *sdp)
 	}
 }
 
+void gfs2_glock_finish_truncate(struct gfs2_inode *ip)
+{
+	struct gfs2_glock *gl = ip->i_gl;
+	int ret;
+
+	ret = gfs2_truncatei_resume(ip);
+	gfs2_assert_withdraw(gl->gl_sbd, ret == 0);
+
+	spin_lock(&gl->gl_spin);
+	clear_bit(GLF_LOCK, &gl->gl_flags);
+	run_queue(gl, 1);
+	spin_unlock(&gl->gl_spin);
+}
+
 static const char *state2str(unsigned state)
 {
 	switch(state) {