On Sat, Feb 17, 2024 at 1:52 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > On Fri, Feb 16 2024 at 22:41, Anup Patel wrote: > > On Fri, Feb 16, 2024 at 9:03 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > >> I don't think that removing the setup protection is correct. > >> > >> Assume you have maxcpus=N on the kernel command line, then the above > >> for_each_online_cpu() loop would result in cpuhp_setup == true when the > >> instances for the not onlined CPUs are set up, no? > > > > A platform can have multiple PLIC instances where each PLIC > > instance targets a subset of HARTs (or CPUs). > > > > Previously (before this patch), we were probing PLIC very early so on > > a platform with multiple PLIC instances, we need to ensure that cpuhp > > setup is done only after PLIC context associated with boot CPU is > > initialized hence the plic_cpuhp_setup_done check. > > > > This patch converts PLIC driver into a platform driver so now PLIC > > instances are probed after all available CPUs are brought-up. In this > > case, the cpuhp setup must be done only after PLIC context of all > > available CPUs are initialized otherwise some of the CPUs crash > > in plic_starting_cpu() due to lack of PLIC context initialization. > > You're missing the point. > > Assume you have 8 CPUs and 2 PLIC instances one for CPU0-3 and one for > CPU4-7. > > Add "maxcpus=4" on the kernel command line, then only the first 4 CPUs > are brought up. > > So at probe time cpu_online_mask has bit 0,1,2,3 set. > > When the first PLIC it probed the loop which checks the context for each > online CPU will not clear cpuhp_setup and the hotplug state is installed. > > Now the second PLIC is probed (the one for the offline CPUs 4-7) and the > loop will again not clear cpuhp_setup and it tries to install the state > again, no? Ahh, yes. Good catch. For the "maxcpus" in kernel command-line, we can't rely on the cpu_online_mask. I will preserve the plic_cpuhp_setup_done check in the next revision. Regards, Anup
