On Mon, May 23, 2022 at 03:12:28PM +0200, Jiri Olsa wrote: > On Thu, May 19, 2022 at 06:54:39AM -0700, Paul E. McKenney wrote: > > On Thu, May 19, 2022 at 01:33:16PM +0200, Jiri Olsa wrote: > > > 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 ;-) > > > > Whew!!! One piece of the problem might be solved, then. ;-) > > > > > > 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 > > > > I would be happy to queue the arch_cpu_idle() portion of your patch on > > -rcu, if that would move things forward. I suspect that additional > > x86_idle() surgery is required, but maybe I am just getting confused > > about what the x86_idle() function pointer can point to. But it looks > > to me like these need further help: > > > > o static void amd_e400_idle(void) > > Plus things it calls, like tick_broadcast_enter() and > > tick_broadcast_exit(). > > > > o static __cpuidle void mwait_idle(void) > > > > So it might not be all that much additional work, even if I have avoided > > confusion about what the x86_idle() function pointer can point to. But > > I do not trust my ability to test this accurately. > > same here ;-) you're right, there will be other places based > on x86_idle function pointer.. I'll check it, but perhaps we > could address that when someone reports that > > jirka Any thoughts on the correct approach? One extreme would be to mark all sorts of things noinstr. Another extreme would be to enclose all sorts of things in RCU_NONIDLE(). Yet another extreme would be to push the rcu_idle_enter() and rcu_idle_exit() calls still deeper into the idle loop. Or does Peter's recent series somehow cover all of this? https://lore.kernel.org/all/20220519212750.656413111@xxxxxxxxxxxxx/ Thanx, Paul
