Re: [PATCH v2 1/1] sched/debug: fix potential deadlock when write to sched_features

[Peter Zijlstra]

On Tue, Jul 31, 2018 at 09:12:22PM +0900, jiada_w...@mentor.com wrote:
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 60caf1fb94e0..7b2997d4a349 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -87,21 +87,21 @@ struct static_key sched_feat_keys[__SCHED_FEAT_NR] = {
>  
>  #undef SCHED_FEAT
>  
> -static void sched_feat_disable(int i)
> +static void sched_feat_disable_cpuslocked(int i)
>  {
> -     static_key_disable(&sched_feat_keys[i]);
> +     static_key_disable_cpuslocked(&sched_feat_keys[i]);
>  }
>  
> -static void sched_feat_enable(int i)
> +static void sched_feat_enable_cpuslocked(int i)
>  {
> -     static_key_enable(&sched_feat_keys[i]);
> +     static_key_enable_cpuslocked(&sched_feat_keys[i]);
>  }
>  #else
> -static void sched_feat_disable(int i) { };
> -static void sched_feat_enable(int i) { };
> +static void sched_feat_disable_cpuslocked(int i) { };
> +static void sched_feat_enable_cpuslocked(int i) { };
>  #endif /* HAVE_JUMP_LABEL */
>  
> -static int sched_feat_set(char *cmp)
> +static int sched_feat_set_cpuslocked(char *cmp)
>  {
>       int i;
>       int neg = 0;
> @@ -117,10 +117,10 @@ static int sched_feat_set(char *cmp)
>  
>       if (neg) {
>               sysctl_sched_features &= ~(1UL << i);
> -             sched_feat_disable(i);
> +             sched_feat_disable_cpuslocked(i);
>       } else {
>               sysctl_sched_features |= (1UL << i);
> -             sched_feat_enable(i);
> +             sched_feat_enable_cpuslocked(i);
>       }
>  
>       return 0;
> @@ -146,9 +146,11 @@ sched_feat_write(struct file *filp, const char __user 
> *ubuf,
>  
>       /* Ensure the static_key remains in a consistent state */
>       inode = file_inode(filp);
> +     cpus_read_lock();
>       inode_lock(inode);
> -     ret = sched_feat_set(cmp);
> +     ret = sched_feat_set_cpuslocked(cmp);
>       inode_unlock(inode);
> +     cpus_read_unlock();
>       if (ret < 0)
>               return ret;
>  

I've made that..

---
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -89,12 +89,12 @@ struct static_key sched_feat_keys[__SCHE
 
 static void sched_feat_disable(int i)
 {
-       static_key_disable(&sched_feat_keys[i]);
+       static_key_disable_cpuslocked(&sched_feat_keys[i]);
 }
 
 static void sched_feat_enable(int i)
 {
-       static_key_enable(&sched_feat_keys[i]);
+       static_key_enable_cpuslocked(&sched_feat_keys[i]);
 }
 #else
 static void sched_feat_disable(int i) { };
@@ -146,9 +146,11 @@ sched_feat_write(struct file *filp, cons
 
        /* Ensure the static_key remains in a consistent state */
        inode = file_inode(filp);
+       cpus_read_lock();
        inode_lock(inode);
        ret = sched_feat_set(cmp);
        inode_unlock(inode);
+       cpus_read_unlock();
        if (ret < 0)
                return ret;