linux-kernel - Re: local_add

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20081219033514.GA7162@Krystal>
Date:	Thu, 18 Dec 2008 22:35:14 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	David Miller <davem@...emloft.net>, rostedt@...dmis.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	paulus@...ba.org, benh@...nel.crashing.org,
	linux-ia64@...r.kernel.org, linux-s390@...r.kernel.org,
	Christoph Lameter <christoph@...eter.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Martin Bligh <mbligh@...gle.com>
Subject: Re: local_add_return

* Rusty Russell (rusty@...tcorp.com.au) wrote:
> On Wednesday 17 December 2008 10:31:55 Mathieu Desnoyers wrote:
> > I think we have two different use-cases here :
> > 
> > - local_t is useful as-is for things such as a tracer, which need to
> >   modify an element of data atomically wrt local interrupts. The
> >   atomic_long_t, in this case, is the correct fallback.
> > - local_count_t could be used for fast counters.
> 
> Hi Mathieu,
> 
>    Complete agreement.
> 
>    I guess I'm biassed towards local_t == counter version, something else
> == nmi-safe version because that's what it was originally.  Looking through
> the tree, there are only 5 users: module, dmaengine and percpu_counter want
> a counter, and tracing and x86 nmi.c want nmi-safe.  There are several other
> places I know of which want local_t-the-counter.
> 
>    I'll prepare a patch which adds nmi_safe_t, and see how it looks.  There's
> no amazing hurry on this, so I won't race to hit the merge window.
> 

OK,

But can we turn what you call "nmi_safe_t" into "local_atomic_t" then ?
Because we have to specify that this type must only be used as part of
per-cpu data with preemption disabled, and we also specify that it is
atomic.

Plus, nmi_safe_t does not make much sense on architectures without NMIs,
where we sometimes disable interrupts to make the modification "atomic"
wrt all other interrupts that can happen.

Mathieu

> Thanks!
> Rusty.

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
--
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/