From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A15D518D62B for ; Tue, 6 Aug 2024 19:34:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722972887; cv=none; b=YQyy3h6CB8qkMd5P/duPGkk4LQCUW8CU4krzwwgkXONd1LdAcOyZGcjxHNod6QrzBmXla7JP/5YB1wn2nd0YM0dsX01P5WxgcseaIR1qFkNg6oWsc9GXHjmJSlP76s1cPUXvYWsMOViO1H/4kKx7L7YfGUmc0zfqKVSfmUXzh44= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722972887; c=relaxed/simple; bh=66+JayvYPW8DSOJhPfdvsTxf4otOJaTKWU9Q989S6+8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QfcrOkYvCPcsW4YtPhgsPtMWAd2HoY67UOh4fG9Qxly9ZDQx/14tQaDHgu32muQjikRV32hwyD1vND5nCu3L9o/sBWUtIIbtOfqQeuxAGj3s8mrxSCF7hYQ18iVoWvbsBOdzQs4IpNQOuD1try5nVSil3oWtgOl+bqq+EGz6FvU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 98C42C32786; Tue, 6 Aug 2024 19:34:44 +0000 (UTC) Date: Tue, 6 Aug 2024 20:34:42 +0100 From: Catalin Marinas To: Baoquan He Cc: Jinjie Ruan , 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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. Thanks. -- Catalin