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Thu, 08 Aug 2024 21:56:36 -0400 X-MC-Unique: lLrDmAUfPZKPUWNQa4x6NQ-1 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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 mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A01801944CCC; Fri, 9 Aug 2024 01:56:33 +0000 (UTC) Received: from localhost (unknown [10.72.112.129]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E10BC300018D; Fri, 9 Aug 2024 01:56:30 +0000 (UTC) Date: Fri, 9 Aug 2024 09:56:25 +0800 From: Baoquan He To: Jinjie Ruan , Catalin Marinas Cc: vgoyal@redhat.com, dyoung@redhat.com, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, chenjiahao16@huawei.com, akpm@linux-foundation.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arm-kernel@lists.infradead.org, Will Deacon Subject: Re: [PATCH -next] crash: Fix riscv64 crash memory reserve dead loop Message-ID: References: <20240802090105.3871929-1-ruanjinjie@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240808_185640_717034_FD829BAB X-CRM114-Status: GOOD ( 30.12 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 08/08/24 at 03:56pm, Jinjie Ruan wrote: > > > On 2024/8/7 3:34, Catalin Marinas wrote: > > On Tue, Aug 06, 2024 at 08:10:30PM +0100, Catalin Marinas wrote: > >> On Fri, Aug 02, 2024 at 06:11:01PM +0800, Baoquan He wrote: > >>> On 08/02/24 at 05:01pm, Jinjie Ruan wrote: > >>>> On RISCV64 Qemu machine with 512MB memory, cmdline "crashkernel=500M,high" > >>>> will cause system stall as below: > >>>> > >>>> Zone ranges: > >>>> DMA32 [mem 0x0000000080000000-0x000000009fffffff] > >>>> Normal empty > >>>> Movable zone start for each node > >>>> Early memory node ranges > >>>> node 0: [mem 0x0000000080000000-0x000000008005ffff] > >>>> node 0: [mem 0x0000000080060000-0x000000009fffffff] > >>>> Initmem setup node 0 [mem 0x0000000080000000-0x000000009fffffff] > >>>> (stall here) > >>>> > >>>> commit 5d99cadf1568 ("crash: fix x86_32 crash memory reserve dead loop > >>>> bug") fix this on 32-bit architecture. However, the problem is not > >>>> completely solved. If `CRASH_ADDR_LOW_MAX = CRASH_ADDR_HIGH_MAX` on 64-bit > >>>> architecture, for example, when system memory is equal to > >>>> CRASH_ADDR_LOW_MAX on RISCV64, the following infinite loop will also occur: > >>> > >>> Interesting, I didn't expect risc-v defining them like these. > >>> > >>> #define CRASH_ADDR_LOW_MAX dma32_phys_limit > >>> #define CRASH_ADDR_HIGH_MAX memblock_end_of_DRAM() > >> > >> arm64 defines the high limit as PHYS_MASK+1, it doesn't need to be > >> dynamic and x86 does something similar (SZ_64T). Not sure why the > >> generic code and riscv define it like this. > >> > >>>> -> reserve_crashkernel_generic() and high is true > >>>> -> alloc at [CRASH_ADDR_LOW_MAX, CRASH_ADDR_HIGH_MAX] fail > >>>> -> alloc at [0, CRASH_ADDR_LOW_MAX] fail and repeatedly > >>>> (because CRASH_ADDR_LOW_MAX = CRASH_ADDR_HIGH_MAX). > >>>> > >>>> Before refactor in commit 9c08a2a139fe ("x86: kdump: use generic interface > >>>> to simplify crashkernel reservation code"), x86 do not try to reserve crash > >>>> memory at low if it fails to alloc above high 4G. However before refator in > >>>> commit fdc268232dbba ("arm64: kdump: use generic interface to simplify > >>>> crashkernel reservation"), arm64 try to reserve crash memory at low if it > >>>> fails above high 4G. For 64-bit systems, this attempt is less beneficial > >>>> than the opposite, remove it to fix this bug and align with native x86 > >>>> implementation. > >>> > >>> And I don't like the idea crashkernel=,high failure will fallback to > >>> attempt in low area, so this looks good to me. > >> > >> Well, I kind of liked this behaviour. One can specify ,high as a > >> preference rather than forcing a range. The arm64 land has different > >> platforms with some constrained memory layouts. Such fallback works well > >> as a default command line option shipped with distros without having to > >> guess the SoC memory layout. > > > > I haven't tried but it's possible that this patch also breaks those > > arm64 platforms with all RAM above 4GB when CRASH_ADDR_LOW_MAX is > > memblock_end_of_DRAM(). Here all memory would be low and in the absence > > of no fallback, it fails to allocate. > > > > So, my strong preference would be to re-instate the current behaviour > > and work around the infinite loop in a different way. > > Hi, baoquan, What's your opinion? > > Only this patch should be re-instate or all the 3 dead loop fix patch? I am not sure which way Catalin suggested to take. Hi Catalin, Could you say more words about your preference so that Jinjie can proceed accordingly? Thanks Baoquan