On Wed, May 18, 2022 at 09:21:18AM -0700, Paul E. McKenney wrote: > On Tue, May 17, 2022 at 12:13:45PM +0200, Jiri Olsa wrote: > > On Mon, May 16, 2022 at 01:49:22PM +0200, Frederic Weisbecker wrote: > > > On Sun, May 15, 2022 at 09:25:35PM -0700, Paul E. McKenney wrote: > > > > On Sun, May 15, 2022 at 10:36:52PM +0200, Jiri Olsa wrote: > > > > > Making arch_cpu_idle and rcu_idle_exit noinstr. Both functions run > > > > > in rcu 'not watching' context and if there's tracer attached to > > > > > them, which uses rcu (e.g. kprobe multi interface) it will hit RCU > > > > > warning like: > > > > > > > > > > [ 3.017540] WARNING: suspicious RCU usage > > > > > ... > > > > > [ 3.018363] kprobe_multi_link_handler+0x68/0x1c0 > > > > > [ 3.018364] ? kprobe_multi_link_handler+0x3e/0x1c0 > > > > > [ 3.018366] ? arch_cpu_idle_dead+0x10/0x10 > > > > > [ 3.018367] ? arch_cpu_idle_dead+0x10/0x10 > > > > > [ 3.018371] fprobe_handler.part.0+0xab/0x150 > > > > > [ 3.018374] 0xffffffffa00080c8 > > > > > [ 3.018393] ? arch_cpu_idle+0x5/0x10 > > > > > [ 3.018398] arch_cpu_idle+0x5/0x10 > > > > > [ 3.018399] default_idle_call+0x59/0x90 > > > > > [ 3.018401] do_idle+0x1c3/0x1d0 > > > > > > > > > > The call path is following: > > > > > > > > > > default_idle_call > > > > > rcu_idle_enter > > > > > arch_cpu_idle > > > > > rcu_idle_exit > > > > > > > > > > The arch_cpu_idle and rcu_idle_exit are the only ones from above > > > > > path that are traceble and cause this problem on my setup. > > > > > > > > > > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx> > > > > > > > > From an RCU viewpoint: > > > > > > > > Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > > > > > > > [ I considered asking for an instrumentation_on() in rcu_idle_exit(), > > > > but there is no point given that local_irq_restore() isn't something > > > > you instrument anyway. ] > > > > > > So local_irq_save() in the beginning of rcu_idle_exit() is unsafe because > > > it is instrumentable by the function (graph) tracers and the irqsoff tracer. > > > > > > Also it calls into lockdep that might make use of RCU. > > > > > > That's why rcu_idle_exit() is not noinstr yet. See this patch: > > > > > > https://lore.kernel.org/lkml/20220503100051.2799723-4-frederic@xxxxxxxxxx/ > > > > I see, could we mark it at least with notrace meanwhile? > > For the RCU part, how about as follows? > > If this approach is reasonable, my guess would be that Frederic will pull > it into his context-tracking series, perhaps using a revert of this patch > to maintain sanity in the near term. > > If this approach is unreasonable, well, that is Murphy for you! I checked and it works in my test ;-) > > For the x86 idle part, my feeling is still that the rcu_idle_enter() > and rcu_idle_exit() need to be pushed deeper into the code. Perhaps > an ongoing process as the idle loop continues to be dug deeper? for arch_cpu_idle with noinstr I'm getting this W=1 warning: vmlinux.o: warning: objtool: arch_cpu_idle()+0xb: call to {dynamic}() leaves .noinstr.text section we could have it with notrace if that's a problem thanks, jirka > > Thanx, Paul > > ------------------------------------------------------------------------ > > commit cd338be719a0a692e0d50e1a8438e1f6c7165d9c > Author: Paul E. McKenney <paulmck@xxxxxxxxxx> > Date: Tue May 17 21:00:04 2022 -0700 > > rcu: Apply noinstr to rcu_idle_enter() and rcu_idle_exit() > > This commit applies the "noinstr" tag to the rcu_idle_enter() and > rcu_idle_exit() functions, which are invoked from portions of the idle > loop that cannot be instrumented. These tags require reworking the > rcu_eqs_enter() and rcu_eqs_exit() functions that these two functions > invoke in order to cause them to use normal assertions rather than > lockdep. In addition, within rcu_idle_exit(), the raw versions of > local_irq_save() and local_irq_restore() are used, again to avoid issues > with lockdep in uninstrumented code. > > This patch is based in part on an earlier patch by Jiri Olsa, discussions > with Peter Zijlstra and Frederic Weisbecker, earlier changes by Thomas > Gleixner, and off-list discussions with Yonghong Song. > > Link: https://lore.kernel.org/lkml/20220515203653.4039075-1-jolsa@xxxxxxxxxx/ > Reported-by: Jiri Olsa <jolsa@xxxxxxxxxx> > Reported-by: Alexei Starovoitov <ast@xxxxxxxxxx> > Reported-by: Andrii Nakryiko <andrii@xxxxxxxxxx> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > Reviewed-by: Yonghong Song <yhs@xxxxxx> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 222d59299a2af..02233b17cce0e 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -635,8 +635,8 @@ static noinstr void rcu_eqs_enter(bool user) > return; > } > > - lockdep_assert_irqs_disabled(); > instrumentation_begin(); > + lockdep_assert_irqs_disabled(); > trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&rdp->dynticks)); > WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current)); > rcu_preempt_deferred_qs(current); > @@ -663,9 +663,9 @@ static noinstr void rcu_eqs_enter(bool user) > * If you add or remove a call to rcu_idle_enter(), be sure to test with > * CONFIG_RCU_EQS_DEBUG=y. > */ > -void rcu_idle_enter(void) > +void noinstr rcu_idle_enter(void) > { > - lockdep_assert_irqs_disabled(); > + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled()); > rcu_eqs_enter(false); > } > EXPORT_SYMBOL_GPL(rcu_idle_enter); > @@ -865,7 +865,7 @@ static void noinstr rcu_eqs_exit(bool user) > struct rcu_data *rdp; > long oldval; > > - lockdep_assert_irqs_disabled(); > + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled()); > rdp = this_cpu_ptr(&rcu_data); > oldval = rdp->dynticks_nesting; > WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0); > @@ -900,13 +900,13 @@ static void noinstr rcu_eqs_exit(bool user) > * If you add or remove a call to rcu_idle_exit(), be sure to test with > * CONFIG_RCU_EQS_DEBUG=y. > */ > -void rcu_idle_exit(void) > +void noinstr rcu_idle_exit(void) > { > unsigned long flags; > > - local_irq_save(flags); > + raw_local_irq_save(flags); > rcu_eqs_exit(false); > - local_irq_restore(flags); > + raw_local_irq_restore(flags); > } > EXPORT_SYMBOL_GPL(rcu_idle_exit); >
