[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>
diff --git a/fs/jffs2/nodemgmt.c b/fs/jffs2/nodemgmt.c
index 747a73f..9df8f3e 100644
--- a/fs/jffs2/nodemgmt.c
+++ b/fs/jffs2/nodemgmt.c
@@ -116,7 +116,10 @@
 			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();