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]
Date:   Mon, 10 Feb 2020 10:46:16 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     "Joel Fernandes, Google" <joel@...lfernandes.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Ingo Molnar <mingo@...hat.com>,
        Richard Fontana <rfontana@...hat.com>,
        rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        paulmck <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Subject: Re: [RFC 0/3] Revert SRCU from tracepoint infrastructure

On Sat, Feb 08, 2020 at 11:31:25AM -0500, Mathieu Desnoyers wrote:
> ----- On Feb 7, 2020, at 3:56 PM, Joel Fernandes, Google joel@...lfernandes.org wrote:
> 
> > Hi,
> > These patches remove SRCU usage from tracepoints. The reason for proposing the
> > reverts is because the whole point of SRCU was to avoid having to call
> > rcu_irq_enter_irqson(). However this was added back in 865e63b04e9b2 ("tracing:
> > Add back in rcu_irq_enter/exit_irqson() for rcuidle tracepoints") because perf
> > was breaking..
> 
> I think the original patch re-enabling the rcu_irq_enter/exit_irqson() is a
> tracepoint band-aid over what should actually been fixed within perf instead.
> 
> Perf should not do rcu_read_lock/unlock()/synchronize_rcu(), but rather use
> tracepoint_synchronize_unregister() to match the read-side provided by
> tracepoints.
> 
> If perf can then just rely on the underlying synchronization provided by each
> instrumentation providers (tracepoint, kprobe, ...) and not explicitly add its own
> unneeded synchronization on top (e.g. rcu_read_lock/unlock), then it should simplify
> all this.

It can't. At this point it doesn't know where the event came from. Also,
the whole perf stuff is per definition non-preemptible, as it needs to
run from NMI context.

Furthermore, using srcu would be detrimental, because of how it has
smp_mb() in the read side primitives.

The best we can do is move that rcu_irq_enter/exit_*() crud into the
perf tracepoint glue I suppose.

Powered by blists - more mailing lists