linux-kernel - Re: [patches] seqlock: add barrier-less special cases for seqcounts

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] [day] [month] [year] [list]

Date:	Mon, 15 Nov 2010 14:49:46 +1100
From:	Nick Piggin <npiggin@...nel.dk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Nick Piggin <npiggin@...nel.dk>, linux-kernel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patches] seqlock: add barrier-less special cases for seqcounts

On Fri, Nov 12, 2010 at 03:52:55PM -0800, Linus Torvalds wrote:
> On Fri, Nov 12, 2010 at 3:06 PM, Nick Piggin <npiggin@...nel.dk> wrote:
> . ...
> > seq2 = read_seqlock_begin(&child->d_seq);
> > if (read_seqcount_retry(&dentry->d_seq, seq))
> >  /* bail out */
> 
> So the only issue is that this particular back-to-back sequence with
> these kinds of "take one seqlock and release the previous one" where
> you currently end up having basically one smp_rmb() at the end of
> "read_seqlock_begin()", only to be followed immediately by another one
> starting out the "read_seqcount_retry()"?

I think basically yes, I'll have to take another look at the code.


> If so, I think we should make _that_ operation ("move from one seqlock
> to another") be the special one, because it smells like in general,
> using the special non-locking versions is going to be a very subtle
> interface.

OK, that sounds like a good idea. I'll see if that's applicable.

--
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/