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SubjectRe: [PATCH] arm64/kernel: Simplify __cpu_up() by bailing out early
On Mon, Mar 02, 2020 at 12:21:35PM +0000, Mark Rutland wrote:
> On Mon, Mar 02, 2020 at 01:03:40PM +1100, Gavin Shan wrote:
> > The function __cpu_up() is invoked to bring up the target CPU through
> > the backend, PSCI for example. The nested if statements won't be needed
> > if we bail out early on the following two conditions where the status
> > won't be checked. The code looks simplified in that case.
> >
> > * Error returned from the backend (e.g. PSCI)
> > * The target CPU has been marked as onlined
> >
> > Signed-off-by: Gavin Shan <gshan@redhat.com>
>
> FWIW, this looks like a nice cleanup to me:
>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Catalin, are you happy to pick this up?

Thanks,
Mark.

> While this patch leaves secondary_data.{task,stack} stale on a
> successful onlining, that was already the case for a timeout, and should
> be fine (since the next attempt at onlining will configure those before
> poking the CPU).
>
> Thanks,
> Mark.
>
> > ---
> > arch/arm64/kernel/smp.c | 79 +++++++++++++++++++----------------------
> > 1 file changed, 37 insertions(+), 42 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> > index d4ed9a19d8fe..2a9d8f39dc58 100644
> > --- a/arch/arm64/kernel/smp.c
> > +++ b/arch/arm64/kernel/smp.c
> > @@ -115,60 +115,55 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
> > update_cpu_boot_status(CPU_MMU_OFF);
> > __flush_dcache_area(&secondary_data, sizeof(secondary_data));
> >
> > - /*
> > - * Now bring the CPU into our world.
> > - */
> > + /* Now bring the CPU into our world */
> > ret = boot_secondary(cpu, idle);
> > - if (ret == 0) {
> > - /*
> > - * CPU was successfully started, wait for it to come online or
> > - * time out.
> > - */
> > - wait_for_completion_timeout(&cpu_running,
> > - msecs_to_jiffies(5000));
> > -
> > - if (!cpu_online(cpu)) {
> > - pr_crit("CPU%u: failed to come online\n", cpu);
> > - ret = -EIO;
> > - }
> > - } else {
> > + if (ret) {
> > pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
> > return ret;
> > }
> >
> > + /*
> > + * CPU was successfully started, wait for it to come online or
> > + * time out.
> > + */
> > + wait_for_completion_timeout(&cpu_running,
> > + msecs_to_jiffies(5000));
> > + if (cpu_online(cpu))
> > + return 0;
> > +
> > + pr_crit("CPU%u: failed to come online\n", cpu);
> > secondary_data.task = NULL;
> > secondary_data.stack = NULL;
> > __flush_dcache_area(&secondary_data, sizeof(secondary_data));
> > status = READ_ONCE(secondary_data.status);
> > - if (ret && status) {
> > -
> > - if (status == CPU_MMU_OFF)
> > - status = READ_ONCE(__early_cpu_boot_status);
> > + if (status == CPU_MMU_OFF)
> > + status = READ_ONCE(__early_cpu_boot_status);
> >
> > - switch (status & CPU_BOOT_STATUS_MASK) {
> > - default:
> > - pr_err("CPU%u: failed in unknown state : 0x%lx\n",
> > - cpu, status);
> > - cpus_stuck_in_kernel++;
> > - break;
> > - case CPU_KILL_ME:
> > - if (!op_cpu_kill(cpu)) {
> > - pr_crit("CPU%u: died during early boot\n", cpu);
> > - break;
> > - }
> > - pr_crit("CPU%u: may not have shut down cleanly\n", cpu);
> > - /* Fall through */
> > - case CPU_STUCK_IN_KERNEL:
> > - pr_crit("CPU%u: is stuck in kernel\n", cpu);
> > - if (status & CPU_STUCK_REASON_52_BIT_VA)
> > - pr_crit("CPU%u: does not support 52-bit VAs\n", cpu);
> > - if (status & CPU_STUCK_REASON_NO_GRAN)
> > - pr_crit("CPU%u: does not support %luK granule \n", cpu, PAGE_SIZE / SZ_1K);
> > - cpus_stuck_in_kernel++;
> > + switch (status & CPU_BOOT_STATUS_MASK) {
> > + default:
> > + pr_err("CPU%u: failed in unknown state : 0x%lx\n",
> > + cpu, status);
> > + cpus_stuck_in_kernel++;
> > + break;
> > + case CPU_KILL_ME:
> > + if (!op_cpu_kill(cpu)) {
> > + pr_crit("CPU%u: died during early boot\n", cpu);
> > break;
> > - case CPU_PANIC_KERNEL:
> > - panic("CPU%u detected unsupported configuration\n", cpu);
> > }
> > + pr_crit("CPU%u: may not have shut down cleanly\n", cpu);
> > + /* Fall through */
> > + case CPU_STUCK_IN_KERNEL:
> > + pr_crit("CPU%u: is stuck in kernel\n", cpu);
> > + if (status & CPU_STUCK_REASON_52_BIT_VA)
> > + pr_crit("CPU%u: does not support 52-bit VAs\n", cpu);
> > + if (status & CPU_STUCK_REASON_NO_GRAN) {
> > + pr_crit("CPU%u: does not support %luK granule\n",
> > + cpu, PAGE_SIZE / SZ_1K);
> > + }
> > + cpus_stuck_in_kernel++;
> > + break;
> > + case CPU_PANIC_KERNEL:
> > + panic("CPU%u detected unsupported configuration\n", cpu);
> > }
> >
> > return ret;
> > --
> > 2.23.0
> >

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