[PATCH] md: Remove bi_end_io call out from under a spinlock

raid5 overloads bi_phys_segments to count the number of blocks that the
request was broken in to so that it knows when the bio is completely handled.

Accessing this must always be done under a spinlock.  In one case we also call
bi_end_io under that spinlock, which probably isn't ideal as bi_end_io could
be expensive (even though it isn't allowed to sleep).

So we reducde the range of the spinlock to just accessing bi_phys_segments.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/md/raid5.c

@@ -1743,6 +1743,7 @@ static int make_request(request_queue_t *q, struct bio * bi)
 	sector_t logical_sector, last_sector;
 	struct stripe_head *sh;
 	const int rw = bio_data_dir(bi);
+	int remaining;
 
 	if (unlikely(bio_barrier(bi))) {
 		bio_endio(bi, bi->bi_size, -EOPNOTSUPP);
@@ -1852,15 +1853,16 @@ static int make_request(request_queue_t *q, struct bio * bi)
 
 	}
 	spin_lock_irq(&conf->device_lock);
-	if (--bi->bi_phys_segments == 0) {
+	remaining = --bi->bi_phys_segments;
+	spin_unlock_irq(&conf->device_lock);
+	if (remaining == 0) {
 		int bytes = bi->bi_size;
 
 		if ( bio_data_dir(bi) == WRITE )
 			md_write_end(mddev);
 		bi->bi_size = 0;
 		bi->bi_end_io(bi, bytes, 0);
 	}
-	spin_unlock_irq(&conf->device_lock);
 	return 0;
 }