linux-kernel - Re: [PATCH v6 1/5] kernel/reboot: emergency_restart: set correct system

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Date:   Thu, 15 Jun 2023 15:21:02 +0200
From:   Francesco Dolcini <francesco@...cini.it>
To:     Nishanth Menon <nm@...com>
Cc:     Benjamin Bara <bbara93@...il.com>, Wolfram Sang <wsa@...nel.org>,
        Lee Jones <lee@...nel.org>, rafael.j.wysocki@...el.com,
        dmitry.osipenko@...labora.com, peterz@...radead.org,
        jonathanh@...dia.com, richard.leitner@...ux.dev,
        treding@...dia.com, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-tegra@...r.kernel.org,
        Benjamin Bara <benjamin.bara@...data.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v6 1/5] kernel/reboot: emergency_restart: set correct
 system_state

Hello Nishanth,

On Wed, Jun 14, 2023 at 07:06:50PM -0500, Nishanth Menon wrote:
> On 21:02-20230509, Benjamin Bara wrote:
> > From: Benjamin Bara <benjamin.bara@...data.com>
> > 
> > As the emergency restart does not call kernel_restart_prepare(), the
> > system_state stays in SYSTEM_RUNNING.
> > 
> > Since bae1d3a05a8b, this hinders i2c_in_atomic_xfer_mode() from becoming
> > active, and therefore might lead to avoidable warnings in the restart
> > handlers, e.g.:
> > 
> > [   12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0
> > [   12.676926] Voluntary context switch within RCU read-side critical section!
> > ...
> > [   12.742376]  schedule_timeout from wait_for_completion_timeout+0x90/0x114
> > [   12.749179]  wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70
> > ...
> > [   12.994527]  atomic_notifier_call_chain from machine_restart+0x34/0x58
> > [   13.001050]  machine_restart from panic+0x2a8/0x32c
> > 
> > Avoid these by setting the correct system_state.
> > 
> > Fixes: bae1d3a05a8b ("i2c: core: remove use of in_atomic()")
> > Cc: stable@...r.kernel.org # v5.2+
> > Signed-off-by: Benjamin Bara <benjamin.bara@...data.com>
> > ---
> >  kernel/reboot.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/kernel/reboot.c b/kernel/reboot.c
> > index 3bba88c7ffc6..6ebef11c8876 100644
> > --- a/kernel/reboot.c
> > +++ b/kernel/reboot.c
> > @@ -74,6 +74,7 @@ void __weak (*pm_power_off)(void);
> >  void emergency_restart(void)
> >  {
> >  	kmsg_dump(KMSG_DUMP_EMERG);
> > +	system_state = SYSTEM_RESTART;
> >  	machine_emergency_restart();
> >  }
> >  EXPORT_SYMBOL_GPL(emergency_restart);
> > 
> > -- 
> > 2.34.1
> > 
> 
> Tested-by: Nishanth Menon <nm@...com>
> 
> This in addition to a deeper bug in our driver seems to have helped
> resolve a report we had been looking at. Tested on beagleplay platform
> 
> https://lore.kernel.org/all/ZGeHMjlnob2GFyHF@francesco-nb.int.toradex.com/

Is this patch going to fix the RCU warning I reported on that email or
it is just part of a more complex solution?

Francesco