linux-kernel - Re: [PATCH next] bio: zero inlined bio

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Message-ID: <20081223080747.GE32491@kernel.dk>
Date:	Tue, 23 Dec 2008 09:07:49 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH next] bio: zero inlined bio_vec

On Tue, Dec 23 2008, Hugh Dickins wrote:
> bvec_alloc_bs() zeroes its bio_vec, and at least __blk_queue_bounce()
> relies upon that: therefore bio_alloc_bioset() must zero the inlined
> bio_vec - without that, lots of nastiness occurs in bounce_end_io and
> blk_rq_map_sg and other places when booting up my PAE box.
> 
> Signed-off-by: Hugh Dickins <hugh@...itas.com>
> ---
> 
>  fs/bio.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> --- linux-next/fs/bio.c	2008-12-21 20:49:25.000000000 +0000
> +++ fixed/fs/bio.c	2008-12-22 21:10:06.000000000 +0000
> @@ -324,6 +324,8 @@ struct bio *bio_alloc_bioset(gfp_t gfp_m
>  			if (nr_iovecs <= BIO_INLINE_VECS) {
>  				idx = 0;
>  				bvl = bio->bi_inline_vecs;
> +				memset(bvl, 0, BIO_INLINE_VECS *
> +							sizeof(struct bio_vec));
>  				nr_iovecs = BIO_INLINE_VECS;
>  			} else {
>  				bvl = bvec_alloc_bs(gfp_mask, nr_iovecs, &idx,

Hmm, where does it die? Nobody should look at the bio_vec index beyond
bio->bi_vcnt, and 0...bio->bi_vcnt-1 should always be initialized due to
the way we fill the entries.

-- 
Jens Axboe

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