jffs2: Fix serious write stall due to erase

Drop the alloc_sem before erasing flash in
jffs2_garbage_collect_pass().
Otherwise writes are put on hold until the erase
has finised.
Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

fs/jffs2/gc.c

@@ -219,13 +219,14 @@ int jffs2_garbage_collect_pass(struct jffs2_sb_info *c)
 	if (!list_empty(&c->erase_complete_list) ||
 	    !list_empty(&c->erase_pending_list)) {
 		spin_unlock(&c->erase_completion_lock);
-		D1(printk(KERN_DEBUG "jffs2_garbage_collect_pass() erasing pending blocks\n"));
-		if (jffs2_erase_pending_blocks(c, 1)) {
 		mutex_unlock(&c->alloc_sem);
+		D1(printk(KERN_DEBUG "jffs2_garbage_collect_pass() erasing pending blocks\n"));
+		if (jffs2_erase_pending_blocks(c, 1))
 			return 0;
-		}
+
 		D1(printk(KERN_DEBUG "No progress from erasing blocks; doing GC anyway\n"));
 		spin_lock(&c->erase_completion_lock);
+		mutex_lock(&c->alloc_sem);
 	}
 
 	/* First, work out which block we're garbage-collecting */