Re: [LKP] [mm, oom] c1e4c54f9c: BUG:KASAN:null-ptr-deref_in_d

[Michal Hocko <mhocko@kernel.org>]

On Mon 30-07-18 19:05:50, David Rientjes wrote:
> On Mon, 30 Jul 2018, Michal Hocko wrote:
> 
> > On Mon 30-07-18 17:03:20, kernel test robot wrote:
> > [...]
> > > [    9.034310] BUG: KASAN: null-ptr-deref in dump_header+0x10c/0x448
> > 
> > Could you faddr2line on the offset please?
> > 
> 
> It's possible that p is NULL when calling dump_header().  In this case we 
> do not want to print any line concerning a victim because no oom kill has 
> occurred.

You are right. I have missed those.

> This code shouldn't be part of dump_header(), which is called from 
> multiple contexts even when an oom kill has not occurred, and is 
> ratelimited.  The single line output should be the canonical way that 
> userspace parses the log for oom victims, we can't ratelimit it.
> 
> The following would be a fix patch, but it will be broken if the cgroup 
> aware oom killer is removed from -mm so that the oom_group stuff can be 
> merged.

cgroup aware oom killer is going to be replaced by a new implementation
IIUC so the fix should be based on the yuzhoujian patch. Ideally to be
resubmitted.

I would just suggest adding it into a function
dump_oom_summary(struct oom_control *oc, struct task_struct *p)

yuzhoujian could you take care of that please?

> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -438,14 +438,6 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
>  
>  	dump_stack();
>  
> -	/* one line summary of the oom killer context. */
> -	pr_info("oom-kill:constraint=%s,nodemask=%*pbl",
> -			oom_constraint_text[oc->constraint],
> -			nodemask_pr_args(oc->nodemask));
> -	cpuset_print_current_mems_allowed();
> -	mem_cgroup_print_oom_context(oc->memcg, p);
> -	pr_cont(",task=%s,pid=%d,uid=%d\n", p->comm, p->pid,
> -		from_kuid(&init_user_ns, task_uid(p)));
>  	if (is_memcg_oom(oc))
>  		mem_cgroup_print_oom_meminfo(oc->memcg);
>  	else {
> @@ -836,7 +828,8 @@ static bool task_will_free_mem(struct task_struct *task)
>  	return ret;
>  }
>  
> -static void __oom_kill_process(struct task_struct *victim)
> +static void __oom_kill_process(struct task_struct *victim,
> +			       struct oom_control *oc)
>  {
>  	struct task_struct *p;
>  	struct mm_struct *mm;
> @@ -883,6 +876,18 @@ static void __oom_kill_process(struct task_struct *victim)
>  		K(get_mm_counter(victim->mm, MM_ANONPAGES)),
>  		K(get_mm_counter(victim->mm, MM_FILEPAGES)),
>  		K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
> +
> +	if (oc) {
> +		/* One line summary for non-group oom kills */
> +		pr_info("oom-kill: constraint=%s, nodemask=%*pbl",
> +			oom_constraint_text[oc->constraint],
> +			nodemask_pr_args(oc->nodemask));
> +		cpuset_print_current_mems_allowed();
> +		mem_cgroup_print_oom_context(oc->memcg, victim);
> +		pr_cont(", task=%s, pid=%d, uid=%d\n",
> +			victim->comm, victim->pid,
> +			from_kuid(&init_user_ns, task_uid(victim)));
> +	}
>  	task_unlock(victim);
>  
>  	/*
> @@ -986,13 +991,13 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
>  	}
>  	read_unlock(&tasklist_lock);
>  
> -	__oom_kill_process(victim);
> +	__oom_kill_process(victim, oc);
>  }
>  
>  static int oom_kill_memcg_member(struct task_struct *task, void *unused)
>  {
>  	get_task_struct(task);
> -	__oom_kill_process(task);
> +	__oom_kill_process(task, NULL);
>  	return 0;
>  }
>  
> @@ -1020,7 +1025,7 @@ static bool oom_kill_memcg_victim(struct oom_control *oc)
>  		    oc->chosen_task == INFLIGHT_VICTIM)
>  			goto out;
>  
> -		__oom_kill_process(oc->chosen_task);
> +		__oom_kill_process(oc->chosen_task, oc);
>  	}
>  
>  out:

-- 
Michal Hocko
SUSE Labs