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    Subject[RFC][PATCH v3 5/6] don't use bio-map in read() path
    Date
    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@jp.fujitsu.com>
    Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
    Cc: Jens Axboe <jens.axboe@oracle.com>
    Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
    ---
    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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