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, 30 insertions, 1 deletions

diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
index 0cfe44f0b6ab..b08d09696b3e 100644
--- a/fs/gfs2/quota.c
+++ b/fs/gfs2/quota.c
@@ -1296,6 +1296,25 @@ static void quotad_check_timeo(struct gfs2_sbd *sdp, const char *msg,
 	}
 }
 
+static void quotad_check_trunc_list(struct gfs2_sbd *sdp)
+{
+	struct gfs2_inode *ip;
+
+	while(1) {
+		ip = NULL;
+		spin_lock(&sdp->sd_trunc_lock);
+		if (!list_empty(&sdp->sd_trunc_list)) {
+			ip = list_entry(sdp->sd_trunc_list.next,
+					struct gfs2_inode, i_trunc_list);
+			list_del_init(&ip->i_trunc_list);
+		}
+		spin_unlock(&sdp->sd_trunc_lock);
+		if (ip == NULL)
+			return;
+		gfs2_glock_finish_truncate(ip);
+	}
+}
+
 /**
  * gfs2_quotad - Write cached quota changes into the quota file
  * @sdp: Pointer to GFS2 superblock
@@ -1310,6 +1329,7 @@ int gfs2_quotad(void *data)
 	unsigned long quotad_timeo = 0;
 	unsigned long t = 0;
 	DEFINE_WAIT(wait);
+	int empty;
 
 	while (!kthread_should_stop()) {
 
@@ -1324,12 +1344,21 @@ int gfs2_quotad(void *data)
 		/* FIXME: This should be turned into a shrinker */
 		gfs2_quota_scan(sdp);
 
+		/* Check for & recover partially truncated inodes */
+		quotad_check_trunc_list(sdp);
+
 		if (freezing(current))
 			refrigerator();
 		t = min(quotad_timeo, statfs_timeo);
 
 		prepare_to_wait(&sdp->sd_quota_wait, &wait, TASK_UNINTERRUPTIBLE);
-		t -= schedule_timeout(t);
+		spin_lock(&sdp->sd_trunc_lock);
+		empty = list_empty(&sdp->sd_trunc_list);
+		spin_unlock(&sdp->sd_trunc_lock);
+		if (empty)
+			t -= schedule_timeout(t);
+		else
+			t = 0;
 		finish_wait(&sdp->sd_quota_wait, &wait);
 	}