Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 11 Aug 2022 20:22:54 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        stable@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Peter Xu <peterx@redhat.com>, Hugh Dickins <hughd@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        John Hubbard <jhubbard@nvidia.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH] sched/all: Change BUG_ON() instances to WARN_ON()
Message-ID: <YvWPThSv65hwuSMl@nvidia.com>
References: <20220808073232.8808-1-david@redhat.com>
 <CAHk-=wiEAH+ojSpAgx_Ep=NKPWHU8AdO3V56BXcCsU97oYJ1EA@mail.gmail.com>
 <1a48d71d-41ee-bf39-80d2-0102f4fe9ccb@redhat.com>
 <CAHk-=wg40EAZofO16Eviaj7mfqDhZ2gVEbvfsMf6gYzspRjYvw@mail.gmail.com>
 <YvSsKcAXISmshtHo@gmail.com>
 <CAHk-=wgqW6zQcAW4i-ARJ8KNZZjw6tP3nn0QimyTWO=j+ZKsLA@mail.gmail.com>
 <YvV0e7UY5yRbHNJQ@casper.infradead.org>
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <YvV0e7UY5yRbHNJQ@casper.infradead.org>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?4onB5umgFGelVRoRbCtqCEuWDhVRtHPeis8FRYEVcm/48JAEBhiSB0qKGWGB?=
 =?us-ascii?Q?YYREM9CgjtCZ7uamKDhCWE5XgerN12PQpQSd964TAZ8UWAzM5AstenkqioKB?=
 =?us-ascii?Q?tvjV/slHy9YBSLlPZfZyjVxZ9QDAosq/QYJ0cRgujSLbHof99q5Oqo62zutN?=
 =?us-ascii?Q?FlBlzID+BOe7b4sriEbfZCDyGNq5cajHO+SGGfhbNyV/qNozTeNHOnCtfsNH?=
 =?us-ascii?Q?junAsjGskDUc6mNHHLAf1zxndUyM3cKITLC+3ErXO8u31EQpwPE7zVbzMctB?=
 =?us-ascii?Q?/a2OQhSmQg54ZTno760cPZPTghQH9mLgv670s9T7SWMSjACtw9xbRiwLqf4s?=
 =?us-ascii?Q?DQMgrlGZhO7P+zStQ9sQ+LBilmyAEm3oJYKsMI4uUJOSvdvocmD9lonvbX0i?=
 =?us-ascii?Q?Ut/PvDT/2EJI1tuLHl6mEXI5gORx4tEhOc0Bz06c20lAgyxtx9cnxQ/bSvox?=
 =?us-ascii?Q?mJHOa+cQLQDj4JCggGuX3aATSturlcQO4R3JaSaBLkSckYF+IvlCfKqpiHMW?=
 =?us-ascii?Q?hL6SU2QTV2cYQk83q035Wn9GGlObb3i0pqPhiHxf+RbaHBMCizLyKXJDHfFC?=
 =?us-ascii?Q?oYH134qzCOrSm8Qp7TISHe9DdCFIsMcsy0lt2JJMw7gc5FFy1cN/C5w8mxZR?=
 =?us-ascii?Q?hlxOolicKVQcCE8nsBxnmskuXvSVW4JKPP4UDCZWC4BJV2huDMsyZizILbrP?=
 =?us-ascii?Q?3xaBk4vj/vpB77ebvrH5XmOznusP6jtSOZalmA4yeseSF5xbUSPpvpv+8uHR?=
 =?us-ascii?Q?GY8+kPYzamMkocUpRKM/YpEZqzpA7zMCWKBVrhoveVzeVIgtGMQ0jbMOTBqr?=
 =?us-ascii?Q?FRSACgvYTZsfovFhOHMLcgzvRymOrr15iVsdqTKMEpRZv9mNtj7pHn96mraQ?=
 =?us-ascii?Q?FKzRWGIDoUhDrGVYJDP9KRvWg9th7FaX1qmgEDpMm7yNlJJCWOoTtvjEwI0C?=
 =?us-ascii?Q?FnKIDD7cg/KMQd+oKusuhV265HnkhI/NzuS27N8H+mwJjfIdtu0Vl6BEKqRT?=
 =?us-ascii?Q?2wKCxnMlQhDrdjPyEu2iRxWNqO536yrkNkySIr/qavO1ICdaSczowV2ZZCOw?=
 =?us-ascii?Q?o4cD2RgdBkMq+mNFH160sMpoP+gn+aQXZYO82JkobASpSICAFZ/5h0Rq82Wv?=
 =?us-ascii?Q?dGZtNedoylwtztVuc6EOC1aJl4/Mj0t/IiUUO9F2/JLtT22cusxLX6gep5MY?=
 =?us-ascii?Q?ClrhQGw0iKnvyySEbUUmlPV6ySh7crhPwRHClSWEHgVr/EIS8faR0PV9VUVS?=
 =?us-ascii?Q?TZ0SYaghURnyQJRMYVcZacHBl13cZKpWu6F2t2YREOT85MOIRyR1OD8gBdcG?=
 =?us-ascii?Q?a//ZMZQdv2wE9GYYSaB3c6GQG2sPAcesk+9r8biXHX4OHDHKocm0RYshGDDS?=
 =?us-ascii?Q?cRZ70l7VgR9Km9r/KR0vVQ19EddTa2qJRw0PgcS1uVjvMwzxzb9iswf2a+57?=
 =?us-ascii?Q?8RQpmmBRRI7lxnBgXsIWQg8j+VJIfdR2P0M2YF/+0hE2j/XmvGnFhszkjHxV?=
 =?us-ascii?Q?nmTB3WmbC2GLEsQXgFdm2C0M6n+UMrXHERUlCQHi9+m3QII53mrOXkjSE6Ja?=
 =?us-ascii?Q?cEdAli9N2bhZq2GQKLuaOFYdELlGCHP/pZ+cOZD0?=
X-OriginatorOrg: Nvidia.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 7e64acf7-4cb4-4378-7e69-08da7bf06baa
X-MS-Exchange-CrossTenant-AuthSource: MN2PR12MB4192.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Aug 2022 23:22:55.8031
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: AlLVtU+jDaHPCirRT18ESAaexBCZB2loipi1ailyZdpLY5uF4QWsvYaoIjQgFeW4
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB6063
X-Spam-Status: No, score=-1.7 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO,
        RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,
        T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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