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Fri, 11 Sep 2026 11:25:02 +0000 (GMT) Received: from [9.43.53.28] (unknown [9.43.53.28]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 11 Sep 2026 11:25:02 +0000 (GMT) Message-ID: Date: Fri, 11 Sep 2026 16:55:01 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [mainline]kdump fails to save vmcore when crash is manually triggered To: Venkat Rao Bagalkote , Madhavan Srinivasan , Ritesh Harjani , Hari Bathini Cc: LKML , linuxppc-dev , Christophe Leroy References: Content-Language: en-US From: Sourabh Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: RLqjSO-hph7nLnzv45xJkiTbXhmrQ2vT X-Proofpoint-Spam-Info: AW1haW4tMjYwOTExMDE1NSBTYWx0ZWRfX4RfSrtvIZye8 x7Yquo5CxrQphHJwwZiHpCL1mC/aIsDqd8xCW7/vPx7m3Yyj6CV0nVN5HeaoMvKLb4INJ//yYnh L1N7UE/MRAWVA8zf3OMxoxt2fRbfYpk= X-Authority-Analysis: v=2.4 cv=E/dYNqdl c=1 sm=1 tr=0 ts=6aa3e515 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=Zwj9PYTxAAAA:20 a=VnNF1IyMAAAA:8 a=X8FTyEh_R9LiEri5cKoA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=bA3UWDv6hWIuX7UZL3qL:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTExMDE1NSBTYWx0ZWRfX/i7x0NjJAaCB Y6slHIx1Ug4RVqHNgjwN0nqJN0kdSy2Ej2zfeDwBRFNgtOVAMnRNzrs4l8uQ0UPmzcWgGyaAQVw 2edIdmBjNBeGx5w/7fEwSyzjAdQk7YoodNnsStWP/fcPoqmh3yhnB4jWtTr8kftX5j93iI648I7 fSDEsLZiTKswxFH5pNu0VFbrOyFyjyfOGSYlHcVkd0/aLcpNiaL4RbiTaKmNypIDZ+bTLgnlfy8 26CVXKxKjedj9xrAfUZyvpm9HZQtgUbIyDF1kf0zmfuMnF+CfSJkoWssnoxvkh1Oi+u3sBGdR9w M5gDt0J35HlUB/bDe0BJQI6Z4q4XyUKTAVJ0+qWcgvGFlpGONxKHuodtavooMSGXWNn1jNuFjBq FQX8Y7EysWIuR5uQnj2Gev96pFLxm8tgXqR6LcH64X+Cn0rgmOlwsB8Lv5KiN29KfXnwTMSRfAp /yu7Z+1wVgOGeewwu7Q== X-Proofpoint-GUID: RLqjSO-hph7nLnzv45xJkiTbXhmrQ2vT X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-11_04,2026-09-09_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 spamscore=0 bulkscore=0 clxscore=1015 impostorscore=0 phishscore=0 adultscore=0 lowpriorityscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609110155 Hello, I root-caused the issue. The issue is with the makedumpfile virtual-to- physical address translation function when using a 4K page size. While performing the virtual-to-physical address translation for 0xc00c000018000000, makedumpfile reads only one page (4K) at the PGD level: code snippet of ppc64_vtop_level4()/makedumpfile.c https://github.com/makedumpfile/makedumpfile/blob/505d15bcc65462c49572f077a75998c6ee8ff7dc/arch/ppc64.c#L400 ```         [...]     level4 = (ulong *)inf    level4 = (ulong *)info->kernel_pgd;     pgdir = (ulong *)((ulong *)level4 + PGD_OFFSET_L4(vaddr));     if (!readmem(VADDR, PAGEBASE(level4), info->page_buf, PAGESIZE())) {         ERRMSG("Can't read PGD page: 0x%llx\n", PAGEBASE(level4));         return NOT_PADDR;     }     pgd_pte = swap64(ULONG((info->page_buf + PAGEOFFSET(pgdir))), swap);         [...] ``` Whereas the PGD table for the current kernel can be up to 64K in size: 64K = 8192 entries × 8 bytes Since makedumpfile reads only 4KB (PAGESIZE) from the PGD base address, it only gets 512 PGD entries. The correct entry for the vmemmap address `0xc00c000018000000` is 6144. The above logic is also true for the memory map address read fail reported in the original report, which is `c00c000020000000`. Note: This failure is observed only with a 4K page size because, with a 64K page size, `makedumpfile` reads all 8192 entries since the page is aligned with the table size. 64K = 8192 entries × 8 bytes. I will fix this issue in makedumpfile tool. Thanks for the report. - Sourabh Jain On 23/04/26 17:29, Venkat Rao Bagalkote wrote: > Hello!! > > IBM CI has reported vmcore save failures when kdump is tested by > triggering a kernel crash via sysrq. > > > Below are the kernel and tool details: > > Upstream kernel version: 7.0.0+ > Upstream kernel commit-id: 2e68039281932e6dc37718a1ea7cbb8e2cda42e6 > > kexec-tools 2.0.32.git > makedumpfile: version 1.7.9 (released on 20 Apr 2026) > > > Error: > > While booting to crash kernel, I see below continous prints in console > logs: > > > [    0.037177] vmcore: Warning: Zero PT_NOTE entries found > [    0.037181] vmcore: Warning: Zero PT_NOTE entries found > [    0.037184] vmcore: Warning: Zero PT_NOTE entries found > [    0.037186] vmcore: Warning: Zero PT_NOTE entries found > > > And During vmcore collection, I see below error. > > > [    9.948432] systemd[1]: Starting kdump-capture.service - Kdump > Vmcore Save Service... >          Starting kdump-capture.service - Kdump Vmcore > Save Service... > > [    9.992306] kdump[408]: [0;1;38:5:185mKdump is using the default > log level(3). > [   10.158555] kdump[526]: saving to > /sysroot/var/crash/127.0.0.1-2026-04-23-06:06:27/ > [   10.164060] kdump[531]: saving vmcore-dmesg.txt to > /sysroot/var/crash/127.0.0.1-2026-04-23-06:06:27/ > [   10.198598] kdump[537]: saving vmcore-dmesg.txt complete > [   10.200376] kdump[539]: saving vmcore > > Checking for memory holes                         : [  0.0 %] / > Checking for memory holes                         : [100.0 %] | > Excluding unnecessary pages                       : [  6.3 %] \       >       WARNING: Invalid free page order: pfn=5a45fc, order=64424509439, > max order=12 > WARNING: Invalid free page order: pfn=621a02, > order=2166518513861132288, max order=12 > WARNING: Invalid free page order: pfn=6697b3, > order=6706141453275365419, max order=12 > WARNING: Invalid free page order: pfn=669b5d, order=69335804542976, > max order=12 > WARNING: Invalid free page order: pfn=66c5a8, > order=14125543804861677568, max order=12 > WARNING: Invalid free page order: pfn=66c661, order=845524441759747, > max order=12 > WARNING: Invalid free page order: pfn=67dadc, > order=17224182427472101376, max order=12 > WARNING: Invalid free page order: pfn=682b38, > order=3103260797896228864, max order=12 > WARNING: Invalid free page order: pfn=682efa, > order=14269216714183933953, max order=12 > WARNING: Invalid free page order: pfn=682efe, order=134217728, max > order=12 > WARNING: Invalid free page order: pfn=68c0a0, > order=3031209642551148544, max order=12 > WARNING: Invalid free page order: pfn=69709d, > order=17296239995740225536, max order=12 > WARNING: Invalid free page order: pfn=6aa909, > order=2166511968028983296, max order=12 > WARNING: Invalid free page order: pfn=6ae921, > order=6273236509957029888, max order=12 > WARNING: Invalid free page order: pfn=6c1456, > order=17296239987150290944, max order=12 > WARNING: Invalid free page order: pfn=6c35a4, > order=14197601399000268800, max order=12 > WARNING: Invalid free page order: pfn=6c5de2, > order=2166511933669244928, max order=12 > WARNING: Invalid free page order: pfn=6d58da, > order=17296239987150290944, max order=12 > WARNING: Invalid free page order: pfn=6d7987, > order=14557325072076374016, max order=12 > WARNING: Invalid free page order: pfn=6dbb95, > order=17944838645085110272, max order=12 > WARNING: Invalid free page order: pfn=709d7d, > order=6273234623090655232, max order=12 > WARNING: Invalid free page order: pfn=709e11, > order=3031203148023726080, max order=12 > WARNING: Invalid free page order: pfn=70c02f, > order=6705580187335000064, max order=12 > WARNING: Invalid free page order: pfn=715384, > order=14990794317172375552, max order=12 > WARNING: Invalid free page order: pfn=715aef, > order=5048255524311662592, max order=12 > WARNING: Invalid free page order: pfn=71a51e, > order=6199767839173706752, max order=12 > WARNING: Invalid free page order: pfn=71aab5, > order=5048255524311662592, max order=12 > WARNING: Invalid free page order: pfn=732e19, order=28147502510048512, > max order=12 > WARNING: Invalid free page order: pfn=739896, > order=17296239987150290944, max order=12 > WARNING: Invalid free page order: pfn=73b956, > order=17296239991445258240, max order=12 > WARNING: Invalid free page order: pfn=73e043, > order=2166511933669244928, max order=12 > WARNING: Invalid free page order: pfn=740049, > order=6705582074453032960, max order=12 > WARNING: Invalid free page order: pfn=760109, > order=6345294104196284416, max order=12 > WARNING: Invalid free page order: pfn=760260, > order=2166511968028983296, max order=12 > WARNING: Invalid free page order: pfn=774eb8, > order=3103267236521967616, max order=12 > WARNING: Invalid free page order: pfn=77949f, > order=3103260802191196160, max order=12 > WARNING: Invalid free page order: pfn=784ac6, order=1971974104455872, > max order=12 > WARNING: Invalid free page order: pfn=785196, > order=2166518513861132288, max order=12 > WARNING: Invalid free page order: pfn=790654, > order=14557325072177037312, max order=12 > WARNING: Invalid free page order: pfn=792cbe, > order=13837309858646983424, max order=12 > WARNING: Invalid free page order: pfn=792dbe, > order=13837309859722035968, max order=12 > WARNING: Invalid free page order: pfn=793779, > order=15351363758810792960, max order=12 > WARNING: Invalid free page order: pfn=7963af, > order=2166511933669244928, max order=12 > WARNING: Invalid free page order: pfn=7bda8a, > order=13837313428760297472, max order=12 > WARNING: Invalid free page order: pfn=7bfbfa, > order=14269094696377647104, max order=12 > WARNING: Invalid free page order: pfn=7c8498, > order=18088873534452400128, max order=12 > WARNING: Invalid free page order: pfn=7d4bf7, order=1441792, max order=12 > WARNING: Invalid free page order: pfn=7db498, > order=18088873534452400128, max order=12 > WARNING: Invalid free page order: pfn=7dba0d, > order=6345292217329909760, max order=12 > WARNING: Invalid free page order: pfn=7dc618, > order=3319440018652528640, max order=12 > WARNING: Invalid free page order: pfn=7e8788, > order=1113619897082537567, max order=12 > readpage_elf: Attempt to read non-existent page at 0x20000000. > readmem: type_addr: 0, addr:c00c000020000000, size:32768 > __exclude_unnecessary_pages: Can't read the buffer of struct page. > create_2nd_bitmap: Can't exclude unnecessary pages. > > makedumpfile Failed. > [   10.687238] kdump[542]: saving vmcore failed, exitcode:1 > [   10.689073] kdump[544]: saving vmcore failed > [   10.699975] kdump[549]: saving the /run/initramfs/kexec-dmesg.log > to /sysroot/var/crash/127.0.0.1-2026-04-23-06:06:27/// > [   10.701749] systemd[1]: kdump-capture.service: Main > process exited, code=exited, status=1/FAILURE > [   10.701933] systemd[1]: [0;1;38:5:185mkdump-capture.service: > Failed with result 'exit-code'. > [FAILED] Failed to start > kdump-capture.service - Kdump Vmcore Save Service. > > [   10.702090] systemd[1]: Failed to start > kdump-capture.service - Kdump Vmcore Save Service. > See 'systemctl status kdump-capture.service' for details. > > [   10.702249] systemd[1]: Startup finished in 3.351s (kernel) + 0 > (initrd) + 7.350s (userspace) = 10.702s. > [   10.702388] systemd[1]: kdump-capture.service: Triggering > OnFailure= dependencies. > [   10.703543] systemd[1]: Stopped target timers.target - Timer Units. > > > > If you happen to fix, this please add below tag. > > > Reported-by: Venkat Rao Bagalkote > > > Regards, > > Venkat. > >