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Mon, 22 May 2023 17:52:00 -0700 (PDT) Date: Mon, 22 May 2023 17:51:59 -0700 (PDT) From: David Rientjes To: Linus Torvalds cc: David Hildenbrand , Andrew Morton , Michal Hocko , Alex Shi , Johannes Weiner , Matthew Wilcox , Alexander Duyck , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch] mm, debug: allow suppressing panic on CONFIG_DEBUG_VM checks In-Reply-To: Message-ID: References: <53dd9df8-e88f-f466-89f9-3fa141a10267@google.com> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="2003089352-356300863-1684803120=:4168530" X-Rspamd-Queue-Id: 9A5304000C X-Rspam-User: X-Stat-Signature: 9676756rnzq3bnmw7hnzezyxgyxkiqae X-Rspamd-Server: rspam01 X-HE-Tag: 1684803122-131475 X-HE-Meta: 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 wf9b6wTc 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --2003089352-356300863-1684803120=:4168530 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT On Mon, 22 May 2023, Linus Torvalds wrote: > On Mon, May 22, 2023 at 11:39 AM David Rientjes wrote: > > > > I think VM_BUG_ON*() and friends are used to crash the kernel for > > debugging so that we get a crash dump and because some variants don't > > exist for VM_WARN_ON(). > > I do think that from a VM developer standpoint, I think it should be > fine to just effectively turn VM_BUG_ON() into WARN_ON_ONCE() together > with panic_on_warn. > > Maybe we could even extend 'panic_on_warn' to be a bitmap and > effectively have a "don't panic on non-VM warnings" option. > I hadn't thought of that approach, it would definitely help us achieve our goal of emitting warnings on a small set of production hosts that we don't want to crash. It's also very clean. Right now kernel.panic_on_warn can either be 0 or 1. We can keep the lowest bit to be "panic on all warnings" and then bit-1 as "panic on debug VM warnings." When CONFIG_DEBUG_VM is enabled, set the new bit by default so there's no behavior change. Then, we can keep VM_BUG_ON*() and friends around and extend them to check whether they should BUG() after the WARN_ON(1) or not. On our production hosts, we'll just set kernel.panic_on_oom to 0. I'll give it a few days to see if anybody else has any comments or concerns; if not, I'll send a v2 based on this. --2003089352-356300863-1684803120=:4168530--