linux-kernel - Re: [RFC PATCH] fs/direct-io.c: Set bi

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Message-ID: <x496299708p.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 27 Jul 2012 10:21:58 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	majianpeng <majianpeng@...il.com>
Cc:	viro <viro@...IV.linux.org.uk>, "Neil Brown" <neilb@...e.de>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-raid <linux-raid@...r.kernel.org>
Subject: Re: [RFC PATCH] fs/direct-io.c: Set bi_rw when alloc bio.

majianpeng <majianpeng@...il.com> writes:

> When exec bio_alloc, the bi_rw is zero.But after calling bio_add_page,
> it will use bi_rw.
> Fox example, in functiion __bio_add_page,it will call merge_bvec_fn().
> The merge_bvec_fn of raid456 will use the bi_rw to judge the merge.
>>> if ((bvm->bi_rw & 1) == WRITE)
>>>		return biovec->bv_len; /* always allow writes to be mergeable */
>
> Signed-off-by: Jianpeng Ma <majianpeng@...il.com>

Good catch.  How did you find this?  Did you experience data corruption
as a result of this oversight, reduced performance due to missed merge
opportunities, or did you just notice it in reviewing the code?

Reviewed-by: Jeff Moyer <jmoyer@...hat.com>

>
> There are many place like this in kernel.If you think this patch ok, i will correct those.
> ---
>  fs/direct-io.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 1faf4cb..77f0bbf 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -349,6 +349,7 @@ dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
>  
>  	bio->bi_bdev = bdev;
>  	bio->bi_sector = first_sector;
> +	bio->bi_rw = dio->rw;
>  	if (dio->is_async)
>  		bio->bi_end_io = dio_bio_end_aio;
>  	else
--
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