Re: [PATCH] mm,oom: Teach lockdep about oom_lock.

[Peter Zijlstra <peterz@infradead.org>]

On Sat, Mar 09, 2019 at 03:02:22PM +0900, Tetsuo Handa wrote:
> @@ -1120,8 +1122,13 @@ void pagefault_out_of_memory(void)
>  	if (mem_cgroup_oom_synchronize(true))
>  		return;
>  
> -	if (!mutex_trylock(&oom_lock))
> +	if (!mutex_trylock(&oom_lock)) {
		/*
		 * Explain why we still need this on the fail back.
		 */
> +		oom_reclaim_acquire(GFP_KERNEL, 0);
> +		oom_reclaim_release(GFP_KERNEL, 0);
>  		return;
> +	}

	/*
	 * This changes the try-lock to a regular lock; because .....
	 * text goes here.
	 */

> +	oom_reclaim_release(GFP_KERNEL, 0);
> +	oom_reclaim_acquire(GFP_KERNEL, 0);
>  	out_of_memory(&oc);
>  	mutex_unlock(&oom_lock);
>  }
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6d0fa5b..e8853a19 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3793,6 +3793,8 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
>  		schedule_timeout_uninterruptible(1);
>  		return NULL;
>  	}

idem

> +	oom_reclaim_release(gfp_mask, order);
> +	oom_reclaim_acquire(gfp_mask, order);
>  
>  	/*
>  	 * Go through the zonelist yet one more time, keep very high watermark

these things might seem 'obvious' now, but I'm sure that the next time I
see this I'll go WTF?!