[JFFS2] Fix jffs2_reserve_space() when all blocks are pending erasure.

When _all_ the blocks were on the erase_pending_list, we could't find a
block to GC from but there was no _actually_ free space, and
jffs2_reserve_space() would get a little unhappy.

Handle this case by returning -EAGAIN from jffs2_garbage_collect_pass().
There are two callers of that function -- jffs2_flush_wbuf_gc(), which
will interpret it as an error and flush the writebuffer by other means,
and jffs2_reserve_space(), which we modify to respond to -EAGAIN with an
immediate call to jffs2_erase_pending_blocks() and another run round the
loop.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

fs/jffs2/gc.c

@@ -221,7 +221,13 @@ int jffs2_garbage_collect_pass(struct jffs2_sb_info *c)
 		jeb = jffs2_find_gc_block(c);
 
 	if (!jeb) {
-		D1 (printk(KERN_NOTICE "jffs2: Couldn't find erase block to garbage collect!\n"));
+		/* Couldn't find a free block. But maybe we can just erase one and make 'progress'? */
+		if (!list_empty(&c->erase_pending_list)) {
+			spin_unlock(&c->erase_completion_lock);
+			mutex_unlock(&c->alloc_sem);
+			return -EAGAIN;
+		}
+		D1(printk(KERN_NOTICE "jffs2: Couldn't find erase block to garbage collect!\n"));
 		spin_unlock(&c->erase_completion_lock);
 		mutex_unlock(&c->alloc_sem);
 		return -EIO;

fs/jffs2/nodemgmt.c

@@ -116,7 +116,10 @@ int jffs2_reserve_space(struct jffs2_sb_info *c, uint32_t minsize,
 			spin_unlock(&c->erase_completion_lock);
 
 			ret = jffs2_garbage_collect_pass(c);
-			if (ret)
+
+			if (ret == -EAGAIN)
+				jffs2_erase_pending_blocks(c, 1);
+			else if (ret)
 				return ret;
 
 			cond_resched();