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

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Date:   Tue, 31 Jul 2018 18:51:01 +0000
From:   "Davis, George" <George_Davis@...tor.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     "Davis, George" <George_Davis@...tor.com>,
        "Wang, Jiada (ESD)" <Jiada_Wang@...tor.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "erosca@...adit-jv.com" <erosca@...adit-jv.com>
Subject: Re: [PATCH v2 1/1] sched/debug: fix potential deadlock when write to
 sched_features



> On Jul 31, 2018, at 8:36 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Tue, Jul 31, 2018 at 09:12:22PM +0900, jiada_wang@...tor.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;
> 

For the record, for both Jiada's v2 and Peter's simplified versions:

Reviewed-and-Tested-by: George G. Davis <george_davis@...tor.com>