Re: [PATCH 1/3] RISC-V: Do not wait indefinitely in __cpu_up

[Anup Patel]

On Thu, Dec 27, 2018 at 4:39 AM Atish Patra  wrote:
>
> In SMP path, __cpu_up waits for other CPU to come online
> indefinitely. This is wrong as other CPU might be disabled
> in machine mode and possible CPU is set to the cpus present
> in DT.
>
> Introduce a completion variable and waits only for a second.
>
> Signed-off-by: Atish Patra 
> ---
>  arch/riscv/kernel/smpboot.c | 14 +++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index 18cda0e8..bb8cd242 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -39,6 +39,7 @@
>
>  void *__cpu_up_stack_pointer[NR_CPUS];
>  void *__cpu_up_task_pointer[NR_CPUS];
> +static DECLARE_COMPLETION(cpu_running);
>
>  void __init smp_prepare_boot_cpu(void)
>  {
> @@ -77,6 +78,7 @@ void __init setup_smp(void)
>
>  int __cpu_up(unsigned int cpu, struct task_struct *tidle)
>  {
> +   int ret = 0;
> int hartid = cpuid_to_hartid_map(cpu);
> tidle->thread_info.cpu = cpu;
>
> @@ -92,10 +94,15 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
>   task_stack_page(tidle) + THREAD_SIZE);
> WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);
>
> -   while (!cpu_online(cpu))
> -   cpu_relax();
> +   wait_for_completion_timeout(_running,
> +   msecs_to_jiffies(1000));
>
> -   return 0;
> +   if (!cpu_online(cpu)) {
> +   pr_crit("CPU%u: failed to come online\n", cpu);
> +   ret = -EIO;
> +   }
> +
> +   return ret;
>  }
>
>  void __init smp_cpus_done(unsigned int max_cpus)
> @@ -121,6 +128,7 @@ asmlinkage void __init smp_callin(void)
>  * a local TLB flush right now just in case.
>  */
> local_flush_tlb_all();
> +   complete(_running);
> /*
>  * Disable preemption before enabling interrupts, so we don't try to
>  * schedule a CPU that hasn't actually started yet.
> --
> 2.7.4
>

Looks good to me.

Reviewed-by: Anup Patel 

[PATCH 1/3] RISC-V: Do not wait indefinitely in __cpu_up

[Atish Patra]

In SMP path, __cpu_up waits for other CPU to come online
indefinitely. This is wrong as other CPU might be disabled
in machine mode and possible CPU is set to the cpus present
in DT.

Introduce a completion variable and waits only for a second.

Signed-off-by: Atish Patra 
---
 arch/riscv/kernel/smpboot.c | 14 +++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index 18cda0e8..bb8cd242 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -39,6 +39,7 @@
 
 void *__cpu_up_stack_pointer[NR_CPUS];
 void *__cpu_up_task_pointer[NR_CPUS];
+static DECLARE_COMPLETION(cpu_running);
 
 void __init smp_prepare_boot_cpu(void)
 {
@@ -77,6 +78,7 @@ void __init setup_smp(void)
 
 int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 {
+   int ret = 0;
int hartid = cpuid_to_hartid_map(cpu);
tidle->thread_info.cpu = cpu;
 
@@ -92,10 +94,15 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
  task_stack_page(tidle) + THREAD_SIZE);
WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);
 
-   while (!cpu_online(cpu))
-   cpu_relax();
+   wait_for_completion_timeout(_running,
+   msecs_to_jiffies(1000));
 
-   return 0;
+   if (!cpu_online(cpu)) {
+   pr_crit("CPU%u: failed to come online\n", cpu);
+   ret = -EIO;
+   }
+
+   return ret;
 }
 
 void __init smp_cpus_done(unsigned int max_cpus)
@@ -121,6 +128,7 @@ asmlinkage void __init smp_callin(void)
 * a local TLB flush right now just in case.
 */
local_flush_tlb_all();
+   complete(_running);
/*
 * Disable preemption before enabling interrupts, so we don't try to
 * schedule a CPU that hasn't actually started yet.
-- 
2.7.4