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Date: Tue, 24 Mar 2020 06:00:00 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Qais Yousef <qais.yousef@....com>
Cc: Davidlohr Bueso <dave@...olabs.net>,
Josh Triplett <josh@...htriplett.org>,
linux-kernel@...r.kernel.org
Subject: Re: Hit WARN_ON() in rcutorture.c:1055
On Tue, Mar 24, 2020 at 11:39:19AM +0000, Qais Yousef wrote:
> On 03/23/20 11:44, Paul E. McKenney wrote:
> > > > > {register, unregister}_pm_notifier() don't seem to be too hard to use.
> > > >
> > > > That part is easy. It would also be necessary to find all the affected
> > > > warnings in rcutorture and suppress them, not only during this time,
> > > > but also for some period of time afterwards. Maybe this is the only one,
> > > > but that would be surprising. ;-)
> > >
> > > Wouldn't be easier to just deinit/init()? ie: treat it like unload/load module.
> > >
> > > But you'll lose some info then that maybe you'd like to keep across
> > > suspend/resume cycles.
> >
> > Hmmm... Are you running rcutorture as a loadable module or built into
> > your kernel? In the latter case, it starts up automatically shortly
> > after boot.
>
> Built-in. Sorry maybe I wasn't clear. I meant something like the attached.
> Which still generates this warning, so yeah I get your point about suppressing
> some warnings in the right places now.
What my approach will be is to think through how to deal with this.
It might be that I can come up with a simple strategy, and if so, I will
make the changes.
But yes, I never had considered this in any of my rcutorture design or
implementation, so there is likely to be 15 years worth of bugs that
would need to be fixed.
Unless I can come up with something a bit more targeted. Which might
happen. It sometimes has in past encounters with this sort of thing. ;-)
Thanx, Paul
> [ 48.898066] rcu-torture: Stopping rcu_torture_fwd_prog task
> [ 48.908998] rcu-torture: Stopping rcu_torture_reader
> [ 48.917052] rcu-torture: Stopping rcu_torture_fakewriter
> [ 48.926987] ------------[ cut here ]------------
> [ 48.927025] WARNING: CPU: 4 PID: 261 at kernel/rcu/rcutorture.c:1085 rcu_torture_writer+0x49c/0xa90
> [ 48.927038] rcu-torture: Stopping rcu_torture_fakewriter
> [ 48.927041] Modules linked in:
> [ 48.927070] CPU: 4 PID: 261 Comm: rcu_torture_wri Not tainted 5.6.0-rc6-00002-g533440e608d2-dirty #540
> [ 48.927085] Hardware name: ARM Juno development board (r2) (DT)
> [ 48.927103] pstate: 00000005 (nzcv daif -PAN -UAO)
> [ 48.927124] pc : rcu_torture_writer+0x49c/0xa90
> [ 48.927144] lr : rcu_torture_writer+0x494/0xa90
> [ 48.927157] sp : ffff800018bfbde0
> [ 48.927172] x29: ffff800018bfbde0 x28: ffff80001426da58
> [ 48.927198] x27: ffff80001426cf08 x26: ffff80001426cf08
> [ 48.927224] x25: ffff8000121b5000 x24: 0000000000000001
> [ 48.927250] x23: ffff80001426d650 x22: ffff80001426b000
> [ 48.927275] x21: ffff800013439000 x20: 0000000000000001
> [ 48.927301] x19: ffff80001426c000 x18: 0000000000000000
> [ 48.927326] x17: 0000000000000000 x16: 0000000000000000
> [ 48.927351] x15: 0000000000000000 x14: 0000000000000000
> [ 48.927376] x13: 0000000000000000 x12: 0000000000000000
> [ 48.927401] x11: 00000000000001fa x10: 0000000000000000
> [ 48.927426] x9 : ffff800013a130a0 x8 : ffff0009757f0850
> [ 48.927450] x7 : 0000000000000000 x6 : ffff800018bfbcc0
> [ 48.927475] x5 : 0000000000000001 x4 : 0000000000000000
> [ 48.927499] x3 : 0000000000000080 x2 : 0000000000000000
> [ 48.927524] x1 : 0000000000000000 x0 : 0000000000000001
> [ 48.927548] Call trace:
> [ 48.927569] rcu_torture_writer+0x49c/0xa90
> [ 48.927590] kthread+0x13c/0x140
> [ 48.927611] ret_from_fork+0x10/0x18
> [ 48.927627] irq event stamp: 34170
> [ 48.927654] hardirqs last enabled at (34169): [<ffff800010114300>] __local_bh_enable_ip+0x98/0x148
> [ 48.927680] hardirqs last disabled at (34170): [<ffff8000100a95d0>] do_debug_exception+0x1a8/0x258
> [ 48.927702] softirqs last enabled at (34168): [<ffff8000101b949c>] rcu_torture_free+0x84/0x98
> [ 48.927725] softirqs last disabled at (34166): [<ffff8000101b9478>] rcu_torture_free+0x60/0x98
> [ 48.927740] ---[ end trace 57f88d092825f447 ]---
>
> Thanks
>
> --
> Qais Yousef
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 1aeecc165b21..defad882b236 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -45,6 +45,7 @@
> #include <linux/sched/sysctl.h>
> #include <linux/oom.h>
> #include <linux/tick.h>
> +#include <linux/suspend.h>
>
> #include "rcu.h"
>
> @@ -1628,7 +1629,7 @@ static int rcu_torture_stall(void *args)
> }
>
> /* Spawn CPU-stall kthread, if stall_cpu specified. */
> -static int __init rcu_torture_stall_init(void)
> +static int rcu_torture_stall_init(void)
> {
> if (stall_cpu <= 0)
> return 0;
> @@ -2008,7 +2009,7 @@ static int rcu_torture_fwd_prog(void *args)
> }
>
> /* If forward-progress checking is requested and feasible, spawn the thread. */
> -static int __init rcu_torture_fwd_prog_init(void)
> +static int rcu_torture_fwd_prog_init(void)
> {
> struct rcu_fwd *rfp;
>
> @@ -2359,7 +2360,7 @@ static void rcutorture_sync(void)
> cur_ops->sync();
> }
>
> -static int __init
> +static int
> rcu_torture_init(void)
> {
> long i;
> @@ -2549,5 +2550,47 @@ rcu_torture_init(void)
> return firsterr;
> }
>
> -module_init(rcu_torture_init);
> -module_exit(rcu_torture_cleanup);
> +static int rcu_torture_notify(struct notifier_block *nb,
> + unsigned long mode, void *_unused)
> +{
> + switch (mode) {
> + case PM_HIBERNATION_PREPARE:
> + case PM_SUSPEND_PREPARE:
> + pr_info("Shutdodwn rcu torture..");
> + rcu_torture_cleanup();
> + break;
> +
> + case PM_POST_RESTORE:
> + pr_info("Restart rcu torture..");
> + rcu_torture_init();
> + break;
> + }
> +
> + return 0;
> +}
> +
> +static struct notifier_block rcu_nb = {
> + .notifier_call = rcu_torture_notify
> +};
> +
> +static int nb_failed;
> +
> +int rcu_torture_module_init(void)
> +{
> + nb_failed = register_pm_notifier(&rcu_nb);
> + if (nb_failed)
> + pr_warn("Failed to register PM notifier");
> +
> + return rcu_torture_init();
> +}
> +
> +void rcu_torture_module_exit(void)
> +{
> + if (!nb_failed)
> + unregister_pm_notifier(&rcu_nb);
> +
> + rcu_torture_cleanup();
> +}
> +
> +module_init(rcu_torture_module_init);
> +module_exit(rcu_torture_module_exit);
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