From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

blk_rq_map_kern is used for kernel internal I/Os. Some callers use
this function with stack buffers but DMA to/from the stack buffers
leads to memory corruption on a non-coherent platform.

This patch make blk_rq_map_kern uses the bounce buffers if a caller
passes a stack buffer (on the all platforms for simplicity).

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 block/blk-map.c |    5 +++++
 1 file changed, 5 insertions(+)

diff -puN block/blk-map.c~block-blk_rq_map_kern-uses-the-bounce-buffers-for-stack-buffers block/blk-map.c
--- a/block/blk-map.c~block-blk_rq_map_kern-uses-the-bounce-buffers-for-stack-buffers
+++ a/block/blk-map.c
@@ -268,6 +268,7 @@ int blk_rq_map_kern(struct request_queue
 	int reading = rq_data_dir(rq) == READ;
 	int do_copy = 0;
 	struct bio *bio;
+	unsigned long stack_mask = ~(THREAD_SIZE - 1);
 
 	if (len > (q->max_hw_sectors << 9))
 		return -EINVAL;
@@ -278,6 +279,10 @@ int blk_rq_map_kern(struct request_queue
 	alignment = queue_dma_alignment(q) | q->dma_pad_mask;
 	do_copy = ((kaddr & alignment) || (len & alignment));
 
+	if (!((kaddr & stack_mask) ^
+	      ((unsigned long)current->stack & stack_mask)))
+		do_copy = 1;
+
 	if (do_copy)
 		bio = bio_copy_kern(q, kbuf, len, gfp_mask, reading);
 	else
_