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@xxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxxx # v5.2+
> > Signed-off-by: Benjamin Bara <benjamin.bara@xxxxxxxxxxx>
> > ---
> > 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@xxxxxx>
>
> 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@xxxxxxxxxxxxxxxxxxxxxxxxxxxx/
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
