Re: [patch 12/18] oom: extract panic helper function

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> There are various points in the oom killer where the kernel must
> determine whether to panic or not.  It's better to extract this to a
> helper function to remove all the confusion as to its semantics.
> 
> Also fix a call to dump_header() where tasklist_lock is not read-
> locked, as required.
> 
> There's no functional change with this patch.
> 
> Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
>  include/linux/oom.h |    1 +
>  mm/oom_kill.c       |   53 +++++++++++++++++++++++++++-----------------------
>  2 files changed, 30 insertions(+), 24 deletions(-)
> 
> diff --git a/include/linux/oom.h b/include/linux/oom.h
> --- a/include/linux/oom.h
> +++ b/include/linux/oom.h
> @@ -22,6 +22,7 @@ enum oom_constraint {
>  	CONSTRAINT_NONE,
>  	CONSTRAINT_CPUSET,
>  	CONSTRAINT_MEMORY_POLICY,
> +	CONSTRAINT_MEMCG,
>  };
>  
>  extern int try_set_zone_oom(struct zonelist *zonelist, gfp_t gfp_flags);
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -505,17 +505,40 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
>  	return oom_kill_task(victim);
>  }
>  
> +/*
> + * Determines whether the kernel must panic because of the panic_on_oom sysctl.
> + */
> +static void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask,
> +				int order)
> +{
> +	if (likely(!sysctl_panic_on_oom))
> +		return;
> +	if (sysctl_panic_on_oom != 2) {
> +		/*
> +		 * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
> +		 * does not panic for cpuset, mempolicy, or memcg allocation
> +		 * failures.
> +		 */
> +		if (constraint != CONSTRAINT_NONE)
> +			return;
> +	}
> +	read_lock(&tasklist_lock);
> +	dump_header(NULL, gfp_mask, order, NULL);
> +	read_unlock(&tasklist_lock);
> +	panic("Out of memory: %s panic_on_oom is enabled\n",
> +		sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
> +}
> +
>  #ifdef CONFIG_CGROUP_MEM_RES_CTLR
>  void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
>  {
>  	unsigned long points = 0;
>  	struct task_struct *p;
>  
> -	if (sysctl_panic_on_oom == 2)
> -		panic("out of memory(memcg). panic_on_oom is selected.\n");
> +	check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, 0);
>  	read_lock(&tasklist_lock);
>  retry:
> -	p = select_bad_process(&points, mem, CONSTRAINT_NONE, NULL);
> +	p = select_bad_process(&points, mem, CONSTRAINT_MEMCG, NULL);
>  	if (!p || PTR_ERR(p) == -1UL)
>  		goto out;
>  
> @@ -616,8 +639,8 @@ retry:
>  
>  	/* Found nothing?!?! Either we hang forever, or we panic. */
>  	if (!p) {
> -		read_unlock(&tasklist_lock);
>  		dump_header(NULL, gfp_mask, order, NULL);
> +		read_unlock(&tasklist_lock);
>  		panic("Out of memory and no killable processes...\n");
>  	}
>  
> @@ -639,9 +662,7 @@ void pagefault_out_of_memory(void)
>  		/* Got some memory back in the last second. */
>  		return;
>  
> -	if (sysctl_panic_on_oom)
> -		panic("out of memory from page fault. panic_on_oom is selected.\n");
> -
> +	check_panic_on_oom(CONSTRAINT_NONE, 0, 0);
>  	read_lock(&tasklist_lock);
>  	/* unknown gfp_mask and order */
>  	__out_of_memory(0, 0, CONSTRAINT_NONE, NULL);
> @@ -688,29 +709,13 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
>  		return;
>  	}
>  
> -	if (sysctl_panic_on_oom == 2) {
> -		dump_header(NULL, gfp_mask, order, NULL);
> -		panic("out of memory. Compulsory panic_on_oom is selected.\n");
> -	}
> -
>  	/*
>  	 * Check if there were limitations on the allocation (only relevant for
>  	 * NUMA) that may require different handling.
>  	 */
>  	constraint = constrained_alloc(zonelist, gfp_mask, nodemask);
> +	check_panic_on_oom(constraint, gfp_mask, order);
>  	read_lock(&tasklist_lock);
> -	if (unlikely(sysctl_panic_on_oom)) {
> -		/*
> -		 * panic_on_oom only affects CONSTRAINT_NONE, the kernel
> -		 * should not panic for cpuset or mempolicy induced memory
> -		 * failures.
> -		 */
> -		if (constraint == CONSTRAINT_NONE) {
> -			dump_header(NULL, gfp_mask, order, NULL);
> -			read_unlock(&tasklist_lock);
> -			panic("Out of memory: panic_on_oom is enabled\n");
> -		}
> -	}
>  	__out_of_memory(gfp_mask, order, constraint, nodemask);
>  	read_unlock(&tasklist_lock);
>  

pulled.


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