linux-kernel - Re: [PATCH 3/4] x86,asm: Re-work smp_store

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: <CA+55aFw8d29E26o4eB8VgbZBC5Ot2y9K=T_yE5Dj0dFdyVgOUA@mail.gmail.com>
Date:	Wed, 28 Oct 2015 06:33:56 +0900
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Davidlohr Bueso <dave@...olabs.net>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 3/4] x86,asm: Re-work smp_store_mb()

On Wed, Oct 28, 2015 at 4:53 AM, Davidlohr Bueso <dave@...olabs.net> wrote:
>
> Note that this might affect callers that could/would rely on the
> atomicity semantics, but there are no guarantees of that for
> smp_store_mb() mentioned anywhere, plus most archs use this anyway.
> Thus we continue to be consistent with the memory-barriers.txt file,
> and more importantly, maintain the semantics of the smp_ nature.

So I dislike this patch, mostly because it now makes it obvious that
smp_store_mb() seems to be totally pointless. Every single
implementation is now apparently WRITE_ONCE+smp_mb(), and there are
what, five users of it, so why not then open-code it?

But more importantly, is the "WRITE_ONCE()" even necessary? If there
are no atomicity guarantees, then why bother with WRTE_ONCE() either?

So with this patch, the whole thing becomes pointless, I feel. (Ok, so
it may have been pointless before too, but at least before this patch
it generated special code, now it doesn't). So why carry it along at
all?

               Linus
--
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/