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
| ||
|
Message-ID: <20151007071948.GT2881@worktop.programming.kicks-ass.net> Date: Wed, 7 Oct 2015 09:19:48 +0200 From: Peter Zijlstra <peterz@...radead.org> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: Josh Triplett <josh@...htriplett.org>, linux-kernel@...r.kernel.org, mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, tglx@...utronix.de, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com, Boqun Feng <boqun.feng@...il.com> Subject: Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers On Tue, Oct 06, 2015 at 02:05:39PM -0700, Paul E. McKenney wrote: > On Tue, Oct 06, 2015 at 10:52:00PM +0200, Peter Zijlstra wrote: > > On Tue, Oct 06, 2015 at 01:18:01PM -0700, Paul E. McKenney wrote: > > > On Tue, Oct 06, 2015 at 10:05:38PM +0200, Peter Zijlstra wrote: > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > > > index b9d9e0249e2f..93c0f23c3e45 100644 > > > > > --- a/kernel/rcu/tree.c > > > > > +++ b/kernel/rcu/tree.c > > > > > @@ -337,12 +337,14 @@ static void rcu_momentary_dyntick_idle(void) > > > > > */ > > > > > void rcu_note_context_switch(void) > > > > > { > > > > > + barrier(); /* Avoid RCU read-side critical sections leaking down. */ > > > > > trace_rcu_utilization(TPS("Start context switch")); > > > > > rcu_sched_qs(); > > > > > rcu_preempt_note_context_switch(); > > > > > if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) > > > > > rcu_momentary_dyntick_idle(); > > > > > trace_rcu_utilization(TPS("End context switch")); > > > > > + barrier(); /* Avoid RCU read-side critical sections leaking up. */ > > > > > } > > > > > EXPORT_SYMBOL_GPL(rcu_note_context_switch); > > > > > > > > These OTOH could be fixed with a noinline, such that the compiler may > > > > never inline it, even with whole-program-optimizations, thereby > > > > guaranteeing a function call boundary or compiler barrier. > > > > > > I like the barrier() with the comment. I expect it will be a bit more > > > robust against toolchain changes. > > > > Don't you in fact already rely on the fact that schedule() is a function > > call and will not be inlined? (it doesn't have noinline and I suppose > > whole program optimizers could go funny on it). > > Probably pretty much everywhere I call schedule(). But I was thinking > that barrier() and the beginning and end of an external function didn't > need to do anything. Is that incorrect? No. My point was more that by removing barrier() from rcu_read_{un,}lock() you hard rely on schedule() being a compiler barrier, and I was thinking you need it to be a function call for that, but this is incorrect. Even without it being a function call, there's explicit compiler barriers in there that even whole program optimizers cannot make go away, so my bad for creating confusion. -- 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/
Powered by blists - more mailing lists