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: <20180620163011.GV3593@linux.vnet.ibm.com>
Date:   Wed, 20 Jun 2018 09:30:11 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Byungchul Park <byungchul.park@....com>, jiangshanlai@...il.com,
        josh@...htriplett.org, mathieu.desnoyers@...icios.com,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        joel@...lfernandes.org
Subject: Re: [RFC 1/2] rcu: Do prepare and cleanup idle depending on in_nmi()

On Wed, Jun 20, 2018 at 12:11:56PM -0400, Steven Rostedt wrote:
> On Wed, 20 Jun 2018 08:56:58 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > OK, so in theory this change is safe from a tracing perspective.  But
> > it does add conditionals to a fastpath.
> 
> Does it?
> 
> I see it replacing two conditions from both rcu_irq_enter/exit() with a
> single one in rcu_nmi_enter/exit(). Sure it adds one to rcu_nmi_enter()
> but that's a far less fast path than rcu_irq_enter(), which this patch
> removes a conditional from.

Fair point.  But I am still a bit nervous about the in_nmi().  That
could be avoided by an argument to rcu_nmi_enter() and rcu_nmi_exit()
(or common-code functions derived from these), and the usual inlining
should eliminate both the argument and the check from generated code.

However, it is also the case that the original invokes
rcu_dynticks_task_exit() before the rcu_dynticks_eqs_exit() and
rcu_cleanup_after_idle() afterwards, and the new code executes them
both afterwards.  Why is this transformation safe?

							Thanx, Paul

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ