From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 66D1AEB64DA for ; Thu, 15 Jun 2023 15:58:00 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=HtfzZGG4; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Qhn4k6g5cz3bWc for ; Fri, 16 Jun 2023 01:57:58 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=HtfzZGG4; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=2604:1380:4641:c500::1; helo=dfw.source.kernel.org; envelope-from=nathan@kernel.org; receiver=lists.ozlabs.org) Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4Qhmwr2S3gz3bnL for ; Fri, 16 Jun 2023 01:51:08 +1000 (AEST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3543D615C3; Thu, 15 Jun 2023 15:51:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A065C433C0; Thu, 15 Jun 2023 15:51:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686844263; bh=4vpbcLIWH8N9kUhfy14gCg44JnNZ7tmcDbTQofjr2PY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=HtfzZGG4h7OB0EE/lQpmPVeug5hEItWTKVdQh4sHq5pkRyi+IBc4bQYhPGfLUyXAE O6q85QbbLOckkkq+ZDCntMP7kzjRH0BvUgQTZTsRtxOQVhMz+kPywYdC329KKPHRCd EzHAMzGxIY08qUxBzBs5hhcSI+TdpRxjxhxRYluzPI7qsWgQhBwbTOga8HmP1oqokR Nfn1KKfQ7SfISyWUrNFe+l7vvHqttosQ0oHQWcCUmbPCzjqzV6ZQmJ6Lgxc8I7me24 3i0BNy8Yi/K34Ad5bteBhAQILk/jkgdXefVdp3M52mTzK8Ji4AXkYMW3KmuCjB1GQn 39zP25YPwdB6Q== Date: Thu, 15 Jun 2023 08:50:59 -0700 From: Nathan Chancellor To: Hugh Dickins Subject: Re: [PATCH v2 07/23] mips: update_mmu_cache() can replace __update_tlb() Message-ID: <20230615155059.GB3665766@dev-arch.thelio-3990X> References: <178970b0-1539-8aac-76fd-972c6c46ec17@google.com> <20230614231758.GA1503611@dev-arch.thelio-3990X> <344a4da-3890-45fd-607e-b5f85ca6ad48@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <344a4da-3890-45fd-607e-b5f85ca6ad48@google.com> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-ia64@vger.kernel.org, David Hildenbrand , Peter Zijlstra , Catalin Marinas , Qi Zheng , linux-kernel@vger.kernel.org, Max Filippov , sparclinux@vger.kernel.org, Alexander Gordeev , Claudio Imbrenda , Will Deacon , Greg Ungerer , linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, Helge Deller , x86@kernel.org, Russell King , Matthew Wilcox , Geert Uytterhoeven , Christian Borntraeger , Alexandre Ghiti , Heiko Carstens , linux-m68k@lists.linux-m68k.org, John Paul Adrian Glaubitz , John David Anglin , Suren Baghdasaryan , linux-arm-kernel@lists.infradead.org, Chris Zankel , Michal Simek , Thomas Bogendoerfer , linux-parisc@vger.kernel.org, linux-mm@kvack.org, linux-mips@vger.kernel.org, linux-riscv@lists.infradead.org, Palmer Dabbelt , "Kirill A. Shutemov" , "Aneesh Kumar K.V" , Andrew Morton , linuxppc-dev@lists.ozlabs.org, "David S. Miller" , Mike Rapoport , Mike Kravetz Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, Jun 14, 2023 at 10:43:30PM -0700, Hugh Dickins wrote: > On Wed, 14 Jun 2023, Hugh Dickins wrote: > > On Wed, 14 Jun 2023, Nathan Chancellor wrote: > > > > > > I just bisected a crash while powering down a MIPS machine in QEMU to > > > this change as commit 8044511d3893 ("mips: update_mmu_cache() can > > > replace __update_tlb()") in linux-next. > > > > Thank you, Nathan, that's very helpful indeed. This patch certainly knew > > that it wanted testing, and I'm glad to hear that it is now seeing some. > > > > While powering down? The messages below look like it was just coming up, > > but no doubt that's because you were bisecting (or because I'm unfamiliar > > with what messages to expect there). It's probably irrelevant information, > > but I wonder whether the (V)machine worked well enough for a while before > > you first powered down and spotted the problem, or whether it's never got > > much further than trying to run init (busybox)? I'm trying to get a feel > > for whether the problem occurs under common or uncommon conditions. Ugh sorry, I have been looking into too many bugs lately and got my wires crossed :) this is indeed a problem when running init (which is busybox, this is a simple Buildroot file system). > > > Unfortunately, I can still > > > reproduce it with the existing fix you have for this change on the > > > mailing list, which is present in next-20230614. > > > > Right, that later fix was only for a build warning, nothing functional > > (or at least I hoped that it wasn't making any functional difference). > > > > Thanks a lot for the detailed instructions below: unfortunately, those > > would draw me into a realm of testing I've never needed to enter before, > > so a lot of time spent on setup and learning. Usually, I just stare at > > the source. > > > > What this probably says is that I should revert most my cleanup there, > > and keep as close to the existing code as possible. But some change is > > needed, and I may need to understand (or have a good guess at) what was > > going wrong, to decide what kind of retreat will be successful. > > > > Back to the source for a while: I hope I'll find examples in nearby MIPS > > kernel source (and git history), which will hint at the right way forward. > > Then send you a patch against next-20230614 to try, when I'm reasonably > > confident that it's enough to satisfy my purpose, but likely not to waste > > your time. > > I'm going to take advantage of your good nature by attaching > two alternative patches, either to go on top of next-20230614. > > mips1.patch, > arch/mips/mm/tlb-r4k.c | 12 +----------- > 1 file changed, 1 insertion(+), 11 deletions(-) > > is by far my favourite. I couldn't see anything wrong with what's > already there for mips, but it seems possible that (though I didn't > find it) somewhere calls update_mmu_cache_pmd() on a page table. So > mips1.patch restores the pmd_huge() check, and cleans up further by > removing the silly pgdp, p4dp, pudp, pmdp stuff: the pointer has now > been passed in by the caller, why walk the tree again? I should have > done it this way before. > > But if that doesn't work, then I'm afraid it will have to be > mips2.patch, > arch/mips/include/asm/pgtable.h | 15 ++++++++++++--- > arch/mips/mm/tlb-r3k.c | 5 ++--- > arch/mips/mm/tlb-r4k.c | 27 ++++++++++++++++++--------- > 3 files changed, 32 insertions(+), 15 deletions(-) > > which reverts all of the original patch and its build warning fix, > and does a pte_unmap() to balance the silly pte_offset_map() there; > with an apologetic comment for this being about the only place in > the tree where I have no idea what to do if ptep were NULL. > > I do hope that you find the first fixes the breakage; but if not, then I hate to be the bearer of bad news but the first patch did not fix the breakage, I see the same issue. > I even more fervently hope that the second will, despite my hating it. > Touch wood for the first, fingers crossed for the second, thanks, Thankfully, the second one does. Thanks for the quick and thoughtful responses! Cheers, Nathan