[PATCH] md: define and use safe_put_page for md

md sometimes call put_page on NULL pointers (treating it like kfree).  This is
not safe, so define and use a 'safe_put_page' which checks for NULL.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 39c10a6..feea4ee 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -136,7 +136,7 @@
 out_free_pages:
 	for (i=0; i < RESYNC_PAGES ; i++)
 		for (j=0 ; j < pi->raid_disks; j++)
-			put_page(r1_bio->bios[j]->bi_io_vec[i].bv_page);
+			safe_put_page(r1_bio->bios[j]->bi_io_vec[i].bv_page);
 	j = -1;
 out_free_bio:
 	while ( ++j < pi->raid_disks )
@@ -156,7 +156,7 @@
 			if (j == 0 ||
 			    r1bio->bios[j]->bi_io_vec[i].bv_page !=
 			    r1bio->bios[0]->bi_io_vec[i].bv_page)
-				put_page(r1bio->bios[j]->bi_io_vec[i].bv_page);
+				safe_put_page(r1bio->bios[j]->bi_io_vec[i].bv_page);
 		}
 	for (i=0 ; i < pi->raid_disks; i++)
 		bio_put(r1bio->bios[i]);
@@ -381,7 +381,7 @@
 			/* free extra copy of the data pages */
 			int i = bio->bi_vcnt;
 			while (i--)
-				put_page(bio->bi_io_vec[i].bv_page);
+				safe_put_page(bio->bi_io_vec[i].bv_page);
 		}
 		/* clear the bitmap if all writes complete successfully */
 		bitmap_endwrite(r1_bio->mddev->bitmap, r1_bio->sector,
@@ -1907,7 +1907,7 @@
 		if (conf->r1bio_pool)
 			mempool_destroy(conf->r1bio_pool);
 		kfree(conf->mirrors);
-		put_page(conf->tmppage);
+		safe_put_page(conf->tmppage);
 		kfree(conf->poolinfo);
 		kfree(conf);
 		mddev->private = NULL;