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Mon, 6 Feb 2023 05:52:02 GMT Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B75D420043; Mon, 6 Feb 2023 05:52:02 +0000 (GMT) Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 106CB20040; Mon, 6 Feb 2023 05:52:01 +0000 (GMT) Received: from [9.43.108.31] (unknown [9.43.108.31]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 6 Feb 2023 05:52:00 +0000 (GMT) Message-ID: <39fbad5f-9341-395d-de43-fb0a25c30f0b@linux.ibm.com> Date: Mon, 6 Feb 2023 11:22:00 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH v8 4/8] crash: add phdr for possible CPUs in elfcorehdr To: Eric DeVolder , linuxppc-dev@ozlabs.org, mpe@ellerman.id.au References: <20230201063841.965316-1-sourabhjain@linux.ibm.com> <20230201063841.965316-5-sourabhjain@linux.ibm.com> <401813b1-9834-f8bc-e035-2fef309d3fa6@oracle.com> Content-Language: en-US From: Sourabh Jain In-Reply-To: <401813b1-9834-f8bc-e035-2fef309d3fa6@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: jWhynz-cvW5nBUHxoMhJDnKgJMkkBqRn X-Proofpoint-ORIG-GUID: NbLuFEt3V94A3M1_pb0kU3AY_HHkBh2l X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.930,Hydra:6.0.562,FMLib:17.11.122.1 definitions=2023-02-06_02,2023-02-03_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 priorityscore=1501 malwarescore=0 suspectscore=0 lowpriorityscore=0 bulkscore=0 adultscore=0 phishscore=0 impostorscore=0 mlxscore=0 spamscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2302060047 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: mahesh@linux.vnet.ibm.com, ldufour@linux.ibm.com, kexec@lists.infradead.org, bhe@redhat.com, hbathini@linux.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 02/02/23 21:07, Eric DeVolder wrote: > > > On 2/1/23 00:38, Sourabh Jain wrote: >> On architectures like PowerPC the crash notes are available for all >> possible CPUs. So let's populate the elfcorehdr for all possible >> CPUs having crash notes to avoid updating elfcorehdr during in-kernel >> crash update on CPU hotplug events. >> >> The similar technique is used in kexec-tool for kexec_load case. >> >> Signed-off-by: Sourabh Jain >> --- >> kernel/crash_core.c | 9 ++++++--- >> 1 file changed, 6 insertions(+), 3 deletions(-) >> >> diff --git a/kernel/crash_core.c b/kernel/crash_core.c >> index 37c594858fd51..898d8d2fe2e2e 100644 >> --- a/kernel/crash_core.c >> +++ b/kernel/crash_core.c >> @@ -364,8 +364,8 @@ int crash_prepare_elf64_headers(struct kimage >> *image, struct crash_mem *mem, >> ehdr->e_ehsize = sizeof(Elf64_Ehdr); >> ehdr->e_phentsize = sizeof(Elf64_Phdr); >> - /* Prepare one phdr of type PT_NOTE for each present CPU */ >> - for_each_present_cpu(cpu) { >> + /* Prepare one phdr of type PT_NOTE for possible CPU with crash >> note. */ >> + for_each_possible_cpu(cpu) { > > Sourabh, > Thomas Gleixner is suggesting moving away from for_each_present_cpu() > to for_each_online_cpu(). Using for_each_online_cpu() is going to the > minimum number of needed, whereas your approach of > for_each_possible_cpu() would be to the maximum number needed. > > What would be the ramifications to ppc for moving towards > for_each_online_cpu()? I was in the impression that if CPU notes are missing for offline CPUs in the elfcorehdr then makedumpfile will mess up the CPU IDs. But somehow replacing for_each_present_cpu with for_each_online_cpu worked on PowerPC, even after disabling a couple of CPUs. So things are fine if we pack PT_LOAD for online CPUs instead of present CPUs but, I need to investigate how makedumpfile is able to map PT_LOAD to online CPUs. - Sourabh Jain