[PATCH] arm64/kernel: Simplify __cpu_up() by bailing out early

[Mark Rutland]

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

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) {
- pr_err("CPU%u: failed in unknown state : 0x%lx\n",
- cpu, status);
- cpus_stuck_in_kernel++;
- break;
- 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 */
- 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) {
+ pr_err("CPU%u: failed in unknown state : 0x%lx\n",
+ cpu, status);
+ cpus_stuck_in_kernel++;
+ break;
+ if (!op_cpu_kill(cpu)) {
+ pr_crit("CPU%u: died during early boot\n", cpu);
break;
- panic("CPU%u detected unsupported configuration\n", cpu);
}
+ pr_crit("CPU%u: may not have shut down cleanly\n", cpu);
+ /* Fall through */
+ 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;
+ panic("CPU%u detected unsupported configuration\n", cpu);
}
return ret;
--
2.23.0

[Catalin Marinas]

Post by Mark Rutland

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

Catalin, are you happy to pick this up?

Yes, it was on my list to pick up already, just haven't got around to it
yet.

[Catalin Marinas]

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

Queued for 5.7. Thanks.