[RFC][PATCH v3 5/6] don't use bio-map in read() path

[KOSAKI Motohiro]

Who know proper fixing way?

=================
Subject: [Untested][RFC][PATCH] don't use bio-map in read() path

__bio_map_user_iov() has wrong usage of get_user_pages_fast().
it doesn't have prevent fork mechanism.

then, it sould be used read-side (memory to device transfer) gup only.

This patch is obviously temporally fix. we can implement fork safe bio_map_user()
the future...


Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Cc: Jens Axboe <jens.axboe@xxxxxxxxxx>
Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
---
 block/blk-map.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: b/block/blk-map.c
===================================================================
--- a/block/blk-map.c	2009-02-21 16:53:21.000000000 +0900
+++ b/block/blk-map.c	2009-04-12 23:36:32.000000000 +0900
@@ -55,7 +55,7 @@ static int __blk_rq_map_user(struct requ
 	 * direct dma. else, set up kernel bounce buffers
 	 */
 	uaddr = (unsigned long) ubuf;
-	if (blk_rq_aligned(q, ubuf, len) && !map_data)
+	if (blk_rq_aligned(q, ubuf, len) && !map_data && !reading)
 		bio = bio_map_user(q, NULL, uaddr, len, reading, gfp_mask);
 	else
 		bio = bio_copy_user(q, map_data, uaddr, len, reading, gfp_mask);
@@ -208,7 +208,7 @@ int blk_rq_map_user_iov(struct request_q
 		}
 	}
 
-	if (unaligned || (q->dma_pad_mask & len) || map_data)
+	if (unaligned || (q->dma_pad_mask & len) || map_data || read)
 		bio = bio_copy_user_iov(q, map_data, iov, iov_count, read,
 					gfp_mask);
 	else


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