linux-kernel - Re: [PATCH v2 alt 2] fs/direct-io.c: don't try to allocate more than BIO_MAX

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Date:	Mon, 17 Jan 2011 13:28:52 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	David Dillow <dillowda@...l.gov>
Cc:	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel\@vger.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2 alt 2]  fs/direct-io.c: don't try to allocate more than BIO_MAX_PAGES in a bio

David Dillow <dillowda@...l.gov> writes:

> When using devices that support max_segments > BIO_MAX_PAGES (256),
> direct IO tries to allocate a bio with more pages than allowed, which
> leads to an oops in dio_bio_alloc(). Clamp the request to the supported
> maximum, and change dio_bio_alloc() to reflect that bio_alloc() will
> always return a bio when called with __GFP_WAIT and a valid number of
> vectors.

I like this version better than the first, just clean up the comment to
conform to CodingStyle and you can add my

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

Be sure to CC akpm on the next posting, as DIO changes usually go in
through his tree.

Cheers,
Jeff

> Signed-off-by: David Dillow <dillowda@...l.gov>
> --
> Second alternate, my preferred that reflects that bio_alloc() cannot
> fail when properly called. I can take or leave the comment.
>
>
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 85882f6..96a01d8 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -325,13 +325,17 @@ void dio_end_io(struct bio *bio, int error)
>  }
>  EXPORT_SYMBOL_GPL(dio_end_io);
>  
> -static int
> +static void
>  dio_bio_alloc(struct dio *dio, struct block_device *bdev,
>  		sector_t first_sector, int nr_vecs)
>  {
>  	struct bio *bio;
>  
> +	/* bio_alloc() is guaranteed to return a bio when called with
> +	 * __GFP_WAIT and we request a valid number of vectors.
> +	 */
>  	bio = bio_alloc(GFP_KERNEL, nr_vecs);
> +	BUG_ON(!bio);
>  
>  	bio->bi_bdev = bdev;
>  	bio->bi_sector = first_sector;
> @@ -342,7 +346,6 @@ dio_bio_alloc(struct dio *dio, struct block_device *bdev,
>  
>  	dio->bio = bio;
>  	dio->logical_offset_in_bio = dio->cur_page_fs_offset;
> -	return 0;
>  }
>  
>  /*
> @@ -583,8 +586,9 @@ static int dio_new_bio(struct dio *dio, sector_t start_sector)
>  		goto out;
>  	sector = start_sector << (dio->blkbits - 9);
>  	nr_pages = min(dio->pages_in_io, bio_get_nr_vecs(dio->map_bh.b_bdev));
> +	nr_pages = min(nr_pages, BIO_MAX_PAGES);
>  	BUG_ON(nr_pages <= 0);
> -	ret = dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages);
> +	dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages);
>  	dio->boundary = 0;
>  out:
>  	return ret;
--
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