Messages in this thread | | | Date | Mon, 2 Mar 2020 14:06:40 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH] arm64/kernel: Simplify __cpu_up() by bailing out early |
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On Tue, Mar 03, 2020 at 12:38:48AM +1100, Gavin Shan wrote: > On 3/2/20 11:21 PM, 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> > > > > 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. > > > > Thanks, Mark. Yeah, it should be fine as you said. There are something else, > which might be not relevant. @secondary_data could be accessed by multiple CPUs > in parallel. For example, the master CPU boots CPU#1 and timeouts to wait it > to be online in 5 seconds. CPU#1 isn't necessarily stuck in somewhere. After > that, CPU#2 is brought up and might be accessing @secondary_data. At this point, > CPU#1 can come back to access it either. However, @secondary_data isn't valid > for CPU#1 anymore.
Sure; I'm aware of improvements that could be made here, but I don't think they need to block this patch.
> I was thinking of something to improve the situation, but not sure if it makes > any sense to do so. There are several options: (1) Make @secondary_data per-cpu > variable, which looks a nature way to go. (2) To shutdown the CPU on timeout. > The shutdown request can be failed to be served in theory, but it seems still > an improvement.
I think #2 is a bad idea, since if the CPU gets into the kernel at all, it may have done stuff (e.g. acquiring locks), and ripping it out is liable to cause more problems.
I think doing #1 might be nice, but some caveats apply.
I'd like to clean up the secondary stack/task hand-over to use an atomic cmpxchg pair, so that we can detect when the secondary has possibly tried to use the stack/task. That requires splitting that from the MMU-off bits from the MMU-on bits, and I'm not sure how well that interacts with #1. It might mean that the per-cpu part isn't that worthwhile.
Thanks, Mark.
> > Thanks, > Gavin > > > > --- > > > 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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