linux-kernel - Re: [PATCH] sched/all: Change BUG_ON() instances to WARN

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Date:   Thu, 11 Aug 2022 20:22:54 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        stable@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Peter Xu <peterx@...hat.com>, Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        John Hubbard <jhubbard@...dia.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH] sched/all: Change BUG_ON() instances to WARN_ON()

On Thu, Aug 11, 2022 at 10:28:27PM +0100, Matthew Wilcox wrote:
> On Thu, Aug 11, 2022 at 01:43:09PM -0700, Linus Torvalds wrote:
> > May I suggest going one step further, and making these WARN_ON_ONCE() instead.
> > 
> > >From personal experience, once some scheduler bug (or task struct
> > corruption) happens, ti often *keeps* happening, and the logs just
> > fill up with more and more data, to the point where you lose sight of
> > the original report (and the machine can even get unusable just from
> > the logging).
> 
> I've been thinking about magically turning all the WARN_ON_ONCE() into
> (effectively) WARN_ON_RATELIMIT().  I had some patches in that direction
> a while ago but never got round to tidying them up for submission.

I often wonder if we have a justification for WARN_ON to even exist, I
see a lot of pressure to make things into WARN_ON_ONCE based on the
logic that spamming makes it useless..

Maybe a global limit of 10 warn ons per minute or something would be
interesting?

Jason