[MTD] [NAND] fix race in nand_base.c

When we mark block bad we have to get chip because this involves
writing to the page's OOB. We hit this bug in UBI - we observed
random obscure crashes when it marks block bad from the background
thread and there is some parallel task which utilizes flash.

This patch also adds a TODO note about BBT table protection which
it seems does not exist.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

drivers/mtd/nand/nand_base.c

@@ -24,6 +24,7 @@
  *	if we have HW ecc support.
  *	The AG-AND chips have nice features for speed improvement,
  *	which are not supported yet. Read / program 4 pages in one go.
+ *	BBT table is not serialized, has to be fixed
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -360,16 +361,19 @@ static int nand_default_block_markbad(struct mtd_info *mtd, loff_t ofs)
 		/* We write two bytes, so we dont have to mess with 16 bit
 		 * access
 		 */
+		nand_get_device(chip, mtd, FL_WRITING);
 		ofs += mtd->oobsize;
 		chip->ops.len = chip->ops.ooblen = 2;
 		chip->ops.datbuf = NULL;
 		chip->ops.oobbuf = buf;
 		chip->ops.ooboffs = chip->badblockpos & ~0x01;
 
 		ret = nand_do_write_oob(mtd, ofs, &chip->ops);
+		nand_release_device(mtd);
 	}
 	if (!ret)
 		mtd->ecc_stats.badblocks++;
+
 	return ret;
 }