[PATCH] fix kernel oops in generic_unplug_device() for md

[Luben Tuikov]

The following patch fixes a kernel oops when doing
blk_unplug_work() (oopses in generic_unplug_device()) for md.

The oops and the original report are here:
http://MARC.10East.com/?l=linux-kernel&m=104706400705154&w=2

The problem is that the md driver provides its own unplug
function (among other things) and blk_unplug_work() assumes
that the generic one would work, but it doesn't and BOOM,
it oopses and dies.

-- 
Luben

--- linux-2.5.64bk6/drivers/block/ll_rw_blk.c.orig	2003-03-11 16:23:55.000000000 -0500
+++ linux-2.5.64bk6/drivers/block/ll_rw_blk.c	2003-03-11 18:38:40.000000000 -0500
@@ -29,6 +29,7 @@

  static void blk_unplug_work(void *data);
  static void blk_unplug_timeout(unsigned long data);
+static int __make_request(request_queue_t *, struct bio *);

  /*
   * For the allocated request tables
@@ -1040,7 +1041,13 @@

  static void blk_unplug_work(void *data)
  {
-	generic_unplug_device(data);
+	request_queue_t *q = data;
+
+	if (q->make_request_fn && q->make_request_fn != __make_request
+	    && q->unplug_fn)
+		q->unplug_fn(data);
+	else
+		generic_unplug_device(data);
  }

  static void blk_unplug_timeout(unsigned long data)
@@ -1246,8 +1253,6 @@
  	return 1;
  }

-static int __make_request(request_queue_t *, struct bio *);
-
  /**
   * blk_init_queue  - prepare a request queue for use with a block device
   * @q:    The &request_queue_t to be initialised