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Mon, 21 Sep 2026 17:20:42 +0000 (GMT) Received: from [9.124.208.199] (unknown [9.124.208.199]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 21 Sep 2026 17:20:42 +0000 (GMT) Message-ID: Date: Mon, 21 Sep 2026 22:50:41 +0530 Precedence: bulk X-Mailing-List: kvm-ppc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Linux PPC] Disable PREEMPT To: =?UTF-8?Q?Michal_Such=C3=A1nek?= Cc: Venkat Rao Bagalkote , "Christophe Leroy (CS GROUP)" , Christian Zigotzky , linuxppc-dev , "kvm-ppc@vger.kernel.org" , Madhavan Srinivasan , Peter Zijlstra , "R.T.Dickinson" , hypexed@yahoo.com.au, mad skateman , Christian Zigotzky , Amit Machhiwal , Gautam Menghani , Harsh Prateek Bora References: <9a58d944-405c-4519-852e-8fa04c22c2db@linux.ibm.com> <1d83264f-8eda-4321-9200-f12897e38cda@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=V/XoQuni c=1 sm=1 tr=0 ts=6ab16773 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VLc2VSdLAAAA:20 a=73RBZPNzplm5LS8RO98A:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=bA3UWDv6hWIuX7UZL3qL:22 X-Proofpoint-ORIG-GUID: ZgBODIZuHd8O_TMLh6Jy8rJCAVqbiAjb X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTIxMDI1MCBTYWx0ZWRfXz4SuDkv/JfRz 23surPU664lGvtJOCbI+mU0OfoYySyMYaTIVSBsq5EL1eLbPm8/bk8dEeysr3Y9DySVQRIy35OO pml2TaCZQzRj8tQ3yBefvc8e6f3bD386/73yyRuCrC+VuATgJZa3eXzUTBcVUANzX7MLPSzPkpI VRE309+DWurk0WDUn2143GINRga30wcw+3JIKwt2AfKooN0OgRIyt2y8nMLuP1ntZh12cIHr/xI jm9a88EIPylpi+OyvZxboeZ2hs4TyN/4ue8MZWhMszIhV+vNorsg3dBmhbLxRkDBcLcXOtorep9 Xgroht+KiGpraLIUDULKuJEJRJ2KBK+mgYMPD+A4yH0BPC8EzvhDpG94V045Z7jk6GbkfyqTrUx zPpMQiKxB9j9xmIOJHQ7DVGRWsraxQ9srOJzL1pQKI3MTmY2vaQoqD+YqZ54gDMFqv42RC48XVK IQC6Oj6nvHVEvMwVVuQ== X-Proofpoint-Spam-Info: AW1haW4tMjYwOTIxMDI1MCBTYWx0ZWRfX7loOA+X9OFSE HS2D1AiKE6iWzgQCq54u8vWYoFRh2oaknEcf9sjjJitLYZgjaRJG07KveYax0BckYBXhs2IswiI nTXrNoXu8rkg7HXf1x0vrDndXUh/sOU= X-Proofpoint-GUID: YtHlhqBN6uFeXpP9rTNxZ6uzIscURXFz 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=2026-09-21_05,2026-09-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 malwarescore=0 clxscore=1015 phishscore=0 bulkscore=0 adultscore=0 lowpriorityscore=0 impostorscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609210250 Hi Michal, On 9/21/26 10:16 PM, Michal Suchánek wrote: > On Mon, Sep 21, 2026 at 10:06:22AM +0200, Michal Suchánek wrote: >> On Thu, Sep 03, 2026 at 03:28:26PM +0200, Michal Suchánek wrote: >>> On Thu, Sep 03, 2026 at 06:06:16PM +0530, Harsh Prateek Bora wrote: >>>> + Amit, Gautam - since they recently came across a similar regression which >>>> is seen with non KVM workload as well. >>>> + Venkat - for CI improvement suggestion below. >>>> >>>> Hi Michal, >>>> >>>> On 03/09/26 5:55 pm, Michal Suchánek wrote: >>> >>>>> >>>>> There is another problem that Linux 7.2.2 often locks up on boot inside >>>>> the guest, and as a result a different kernel is needed in the guest to >>>>> reproduce the host crash. This is more recent, linux 6.12 does not have >>>>> this problem. Will try some different kernel combinations to see if I >>>>> can narrow this down. For this the repro is merely booting the kernel in >>>>> the VM, it typically fails early before userspace produces any messages. >>> >>> This one regressed between 6.19.12 >>> https://github.com/openSUSE/kernel-source/blob/9f6830f/config/ppc64le/default >>> and 7.0.12 >>> https://github.com/openSUSE/kernel-source/blob/2ebf0bc/config/ppc64le/default >> >> Which is when preempt was enabled. >> >> Very likely preexisting problem that was exposed by enabling preemption >> again. >> >> @@ -121,9 +122,7 @@ CONFIG_BPF_LSM=y >> >> CONFIG_PREEMPT_BUILD=y >> CONFIG_ARCH_HAS_PREEMPT_LAZY=y >> -# CONFIG_PREEMPT_NONE is not set >> -CONFIG_PREEMPT_VOLUNTARY=y >> -# CONFIG_PREEMPT is not set >> +CONFIG_PREEMPT=y >> # CONFIG_PREEMPT_LAZY is not set >> CONFIG_PREEMPT_COUNT=y >> CONFIG_PREEMPTION=y > > Looking more into this the problem is not reproducible with 6.19 with > full preempt, and can be reproduced with 7.0 with full preempt where > preemtion is mandatory. It only so happens that 1.19 was last kernel > where preemption was not mandatory and where this problem also happened > to not manifest with the Tumbleweed config. > I am bit confused. Is it different problem than the kprobe/bpf issue which was observed on host? Is this kvm/guest specific problem you are observing? Is it still seen even with that kprobe/bpf fix? > It is not deterministic enough to bisect. It's probably some kind of > race condition or code generation problem that can surface and go away > or become too difficult to reproduce with seemingly unrelated changes. > Can you try latest kernel? There was change recently to move to use generic transfer to guest mode work. i.e VIRT_XFER_TO_GUEST_WORK. > Crash happens very early but it's eemu so the memory can be saved > regardelss. The problem is that the crash tool refuses to load the core > bacause it detects the core as SMP and vmlinux as non-SMP or the other > way around. > > Thanks > > Michal >