linux-kernel - Re: [PATCH] mm: ratelimit oversized kvmalloc warnings instead of once

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Date: Wed, 19 Jun 2024 09:19:41 +0200
From: Michal Hocko <mhocko@...e.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	kernel-team@...a.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Kyle McMartin <kyle@...radead.org>
Subject: Re: [PATCH] mm: ratelimit oversized kvmalloc warnings instead of once

On Tue 18-06-24 14:34:21, Shakeel Butt wrote:
> At the moment oversize kvmalloc warnings are triggered once using
> WARN_ON_ONCE() macro. One issue with this approach is that it only
> detects the first abuser and then ignores the remaining abusers which
> complicates detecting all such abusers in a timely manner. The situation
> becomes worse when the repro has low probability and requires production
> traffic and thus require large set of machines to find such abusers. In
> Mera production, this warn once is slowing down the detection of these
> abusers. Simply replace WARN_ON_ONCE with WARN_RATELIMIT.

Long time ago, I've had a patch to do the once_per_callsite WARN. I
cannot find reference at the moment but it used stack depot to note
stacks that have already triggered. Back then there was no reponse on
the ML. Should I try to dig deep and recover it from my archives? I
think this is exactly kind of usecase where it would fit.

> Reported-by: Kyle McMartin <kyle@...radead.org>
> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
> ---
>  mm/util.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/util.c b/mm/util.c
> index 10f215985fe5..de36344e8d53 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -649,7 +649,8 @@ void *kvmalloc_node_noprof(size_t size, gfp_t flags, int node)
>  
>  	/* Don't even allow crazy sizes */
>  	if (unlikely(size > INT_MAX)) {
> -		WARN_ON_ONCE(!(flags & __GFP_NOWARN));
> +		WARN_RATELIMIT(!(flags & __GFP_NOWARN), "size = %zu > INT_MAX",
> +			       size);
>  		return NULL;
>  	}
>  
> -- 
> 2.43.0

-- 
Michal Hocko
SUSE Labs