linux-kernel - Re: [PATCH v5 03/12] block: Add bio

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20120809060019.GA2845@dhcp-172-17-108-109.mtv.corp.google.com>
Date:	Wed, 8 Aug 2012 23:00:19 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, axboe@...nel.dk, agk@...hat.com,
	neilb@...e.de, drbd-dev@...ts.linbit.com, vgoyal@...hat.com,
	mpatocka@...hat.com, sage@...dream.net, yehuda@...newdream.net
Subject: Re: [PATCH v5 03/12] block: Add bio_reset()

Hello,

On Wed, Aug 08, 2012 at 05:07:11PM -0700, Kent Overstreet wrote:
> > > +void bio_reset(struct bio *bio)
> > > +{
> > > +	unsigned long flags = bio->bi_flags & (~0UL << BIO_RESET_BITS);
> > 
> > How many flags are we talking about?  If there aren't too many, I'd
> > prefer explicit BIO_FLAGS_PRESERVED or whatever.
> 
> It mostly isn't actual flags that are preserved - the high bits of the
> flags are used for indicating what slab the bvec was allocated from, and
> that's the main thing that has to be preserved.
> 
> So that's why I went with defining the things that are reset instead of
> the things that are preserved.
> 
> I would prefer if bitfields were used for at least BIO_POOL_IDX, but the
> problem is flags is used as an atomic bit vector for BIO_UPTODATE.
> 
> But flags isn't treated as an atomic bit vector elsewhere -
> bio_flagged() doesn't use test_bit(), and flags are set/cleared with

Not using test_bit() may not be necessarily wrong.

> atomic bit operations in some places but not in others (probably _most_
> of them are technically safe, but... ick).

Mixing atomic and non-atomic modifications is almost always wrong tho.

Anyways, understood.  Can you *please* put some comment what bits are
being preserved across reset then?  Things like this aren't obvious at
all and need ample explanation.

Thanks.

-- 
tejun
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/