On 18/09/2022 10:58, Guilherme G. Piccoli wrote: > On 19/08/2022 19:17, 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> >> Monthly ping - let me know if there's something I should improve in order this fix is considered! Thanks, Guilherme
