On 19/07/2022 16:53, Guilherme G. Piccoli wrote: > Currently the regular CPU shutdown path for ARM disables IRQs/FIQs > in the secondary CPUs - smp_send_stop() calls ipi_cpu_stop(), which > is responsible for that. IRQs are architecturally masked when we > take an interrupt, but FIQs are high priority than IRQs, hence they > aren't masked. With that said, it makes sense to disable FIQs here, > but there's no need for (re-)disabling IRQs. > > More than that: there is an alternative path for disabling CPUs, > in the form of function crash_smp_send_stop(), which is used for > kexec/panic path. This function relies on a SMP call that also > triggers a busy-wait loop [at machine_crash_nonpanic_core()], but > without disabling FIQs. This might lead to odd scenarios, like > early interrupts in the boot of kexec'd kernel or even interrupts > in secondary "disabled" CPUs while the main one still works in the > panic path and assumes all secondary CPUs are (really!) off. > > So, let's disable FIQs in both paths and *not* disable IRQs a second > time, since they are already masked in both paths by the architecture. > This way, we keep both CPU quiesce paths consistent and safe. > > Cc: Marc Zyngier <maz@xxxxxxxxxx> > Cc: Michael Kelley <mikelley@xxxxxxxxxxxxx> > Cc: Russell King <linux@xxxxxxxxxxxxxxx> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> > > --- > > V2: > - Small wording improvement (thanks Michael Kelley); > - Only disable FIQs, since IRQs are masked by architecture > definition when we take an interrupt. Thanks a lot Russell > and Marc for the discussion [0]. > > Should we add a Fixes tag here? If so, maybe the proper target is: > b23065313297 ("ARM: 6522/1: kexec: Add call to non-crashing cores through IPI") > > [0] https://lore.kernel.org/lkml/Ymxcaqy6DwhoQrZT@xxxxxxxxxxxxxxxxxxxxx/ > > arch/arm/kernel/machine_kexec.c | 2 ++ > arch/arm/kernel/smp.c | 5 ++--- > 2 files changed, 4 insertions(+), 3 deletions(-) > [...] Hi Mark / Russell, do you think this one is good enough or is there room for improvement? Appreciate the reviews! Cheers, Guilherme