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Tue, 24 Mar 2026 14:08:54 +0800 (CST) Received: from dggpemf500011.china.huawei.com (unknown [7.185.36.131]) by mail.maildlp.com (Postfix) with ESMTPS id B7AF22012A; Tue, 24 Mar 2026 14:14:23 +0800 (CST) Received: from [10.67.109.254] (10.67.109.254) by dggpemf500011.china.huawei.com (7.185.36.131) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 24 Mar 2026 14:14:20 +0800 Message-ID: Date: Tue, 24 Mar 2026 14:14:18 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.2.0 Subject: Re: [PATCH v9 0/5] arm64/riscv: Add support for crashkernel CMA reservation Content-Language: en-US To: Sourabh Jain , Andrew Morton CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , References: <20260323072745.2481719-1-ruanjinjie@huawei.com> <20260323095548.fa4e13d6e8ae5005ae585e13@linux-foundation.org> <4cfde40c-673a-12b0-dfc5-703d582d6ea9@huawei.com> <595e793d-adc3-4acb-af18-f0a3cf2d5e73@linux.ibm.com> From: Jinjie Ruan In-Reply-To: <595e793d-adc3-4acb-af18-f0a3cf2d5e73@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: kwepems200001.china.huawei.com (7.221.188.67) To dggpemf500011.china.huawei.com (7.185.36.131) On 2026/3/24 12:29, Sourabh Jain wrote: > > > On 24/03/26 09:32, Jinjie Ruan wrote: >> >> On 2026/3/24 0:55, Andrew Morton wrote: >>> On Mon, 23 Mar 2026 15:27:40 +0800 Jinjie Ruan >>> wrote: >>> >>>> The crash memory allocation, and the exclude of crashk_res, >>>> crashk_low_res >>>> and crashk_cma memory are almost identical across different >>>> architectures, >>>> This patch set handle them in crash core in a general way, which >>>> eliminate >>>> a lot of duplication code. >>>> >>>> And add support for crashkernel CMA reservation for arm64 and riscv. >>> Thanks.  AI review has completed and it asks questions: >>>     https://sashiko.dev/#/patchset/20260323072745.2481719-1-ruanjinjie@huawei.com >> I believe it identified 4 valid issues: >> >> - The already discovered crashk_low_res not excluded bug in the existing >> RISC-V code. >> >> - An existing memory leak issue in the existing PowerPC code. > > Yes and suggested approach to fix the issue looks good. > Which is basically replace return with goto out. > > diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c > index 898742a5205c..1426d2099bad 100644 > --- a/arch/powerpc/kexec/crash.c > +++ b/arch/powerpc/kexec/crash.c > @@ -440,7 +440,7 @@ static void update_crash_elfcorehdr(struct kimage > *image, struct memory_notify * >         ret = get_crash_memory_ranges(&cmem); >         if (ret) { >                 pr_err("Failed to get crash mem range\n"); > -               return; > +               goto out; >         } > >         /* > > Are you planning to handle this in this patch series? Or do you want me > to send a separate fix patch? Yes, will fix it in v10, thanks for the clarification. Best regards, Jinjie > > >> >> - The ordering issue of adding CMA ranges to "linux,usable-memory-range". >> >> - An existing concurrency issue. A Concurrent memory hotplug may occur >> between reading memblock and attempting to fill cmem during kexec_load() >> for almost all existing architectures，I'm not sure if this is a >> practical issue in reality.. What are your thoughts on this concurrency issue? >> >>   Race Condition Scenario >> >>    Timeline: >>    --------------------------------------------------------------------- >>    T1: kexec_load() syscall starts >>    T2: kexec_trylock() acquires kexec_lock >>    T3: crash_prepare_headers() is called >>    T4: arch_get_system_nr_ranges() queries memblock → finds 100 memory >> ranges >>    T5: cmem = alloc_cmem(100) allocates buffer for 100 ranges >>    T6: [RACE WINDOW] Another process triggers memory hotplug >>    T7: add_memory() → lock_device_hotplug() → memblock_add_node() >>    T8: New memory region added to memblock >>    T9: arch_crash_populate_cmem() iterates: now finds 102 ranges >>    T10: cmem->ranges[100] → OUT OF BOUNDS WRITE! >>    T11: cmem->ranges[101] → OUT OF BOUNDS WRITE! >>    T12: Kernel crash or memory corruption >> >>    Why This Happens >> >>    1. Different locks used: >>      - kexec_load() uses kexec_trylock (atomic_t) >>      - Memory hotplug uses device_hotplug_lock (mutex) >>    2. No synchronization between these two operations >>    3. Time-of-check to time-of-use (TOCTOU) issue: >>      - Step T4-T5: We query the number of ranges and allocate buffer >>      - Step T6-T9: Memory hotplug adds new ranges between query and >> population >> >> >> >> Any comments or suggestions on the following approach? >> >> >> int crash_prepare_headers(...) >>    { >>        unsigned int max_nr_ranges; >>        struct crash_mem *cmem; >>        int ret; >> >>        lock_device_hotplug(); >> >>        max_nr_ranges = arch_get_system_nr_ranges(); >>        // ... >>        ret = arch_crash_populate_cmem(cmem); >>        // ... >> >>        unlock_device_hotplug(); >>        return ret; >>    } >> >> >