From mboxrd@z Thu Jan  1 00:00:00 1970
From: NeilBrown <neilb@suse.de>
Subject: Re: [RAID0] Possible bug in raid0_make_request() function
Date: Thu, 17 May 2012 17:09:58 +1000
Message-ID: <20120517170958.5ea15635@notabene.brown>
References: <CANSbrrqyj6wL=VBHdgDP7mpjRc+tjZnCQ6rP3_4vHYtPQPqcEA@mail.gmail.com>
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To: Anuj Goel <agoel@cs.stonybrook.edu>
Cc: Linux RAID <linux-raid@vger.kernel.org>
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On Thu, 17 May 2012 02:50:28 -0400 Anuj Goel <agoel@cs.stonybrook.edu> wrot=
e:

> Hi Guys,
> I was going through the RAID0 code and found that there could be a
> possible bug in the=A0raid0_make_request() function.

Thanks.  I love it when people read the md/raid code and report what they
find!!

>=20
> Consider the below snippet of this function.
>=20
> /* This is a one page bio that upper layers
> * refuse to split for us, so we need to split it.
> */
> if (likely(is_power_of_2(chunk_sects)))
> bp =3D bio_split(bio, chunk_sects - (sector &
> =A0 (chunk_sects-1)));
> else
> bp =3D bio_split(bio, chunk_sects -
> =A0 =A0 =A0 sector_div(sector, chunk_sects));
> raid0_make_request(mddev, &bp->bio1);
> raid0_make_request(mddev, &bp->bio2);
> bio_pair_release(bp);
> return;
>=20
> In function bio_split(..), if mempool_alloc() fails, we return NULL into =
bp.
> Now the call raid0_make_request(mddev, &bp->bio1) does not check for
> bp to be not NULL before de-referencing it.
>=20
> Could this be a problem ?

No.  mempool_alloc can only fail if __GFP_WAIT it not passed in,
and bio_split calls it with GFP_NOIO which contains __GFP_WAIT.

So the=20
   if (!bp)
      return bp;

at the top of bio_split is completely pointless - bp will never be NULL.

NeilBrown


>=20
> --
> Best Regards,
> Anuj Goel
> --
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