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Mon, 12 Jan 2026 03:15:02 +0000 Received: from smtpav03.dal12v.mail.ibm.com (smtpav03.dal12v.mail.ibm.com [10.241.53.102]) by smtprelay06.wdc07v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 60C3F0i6787140 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 12 Jan 2026 03:15:00 GMT Received: from smtpav03.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1C8D258061; Mon, 12 Jan 2026 03:15:00 +0000 (GMT) Received: from smtpav03.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CB1DE58056; Mon, 12 Jan 2026 03:14:57 +0000 (GMT) Received: from [9.61.246.85] (unknown [9.61.246.85]) by smtpav03.dal12v.mail.ibm.com (Postfix) with ESMTP; Mon, 12 Jan 2026 03:14:57 +0000 (GMT) Message-ID: <40c12a32-4e7c-4aa5-a77d-939468ca0e07@linux.ibm.com> Date: Mon, 12 Jan 2026 08:44:55 +0530 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: powerpc: BUG: Kernel NULL pointer when running with bcc tools Content-Language: en-GB To: Shrikanth Hegde , Madhavan Srinivasan , linuxppc-dev Cc: Ritesh Harjani , Athira Rajeev , hbathini@linux.ibm.com, "Christophe Leroy (CS GROUP)" References: <2a71b853-f461-4327-8d44-ef97564b2b91@linux.ibm.com> From: Venkat Rao Bagalkote In-Reply-To: <2a71b853-f461-4327-8d44-ef97564b2b91@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: g93lDSBhAnn6IzfWnUZ_St91yTxvteTl X-Authority-Analysis: v=2.4 cv=dYyNHHXe c=1 sm=1 tr=0 ts=69646737 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=gkb95ddqhdx2lPl-xGcA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTEyMDAyMiBTYWx0ZWRfX3Tu+2Jbygc8E gapkR98YYT86mzbUmLlnO/eEUCrv6fqg3CV/MvVKUuIZTi+lxU22NaR4O2VSEuG9tMsBLDxDp8o ZGi/+lJjAKlyQiNhJbstHqmkjo5Ij9CKQBEvAX1bqKcmrCq0smGLTXqGp0zBEZAUIWHs7//VvLw 1ruuvnx5+37FVNjbOymRDqTJ0oFmpQSolBDRzsJ/NMjdAAyRuiVOOtSFeAXzPuHcJFwWJJGOuZE schsUrj2WV5u+UH0o8y8ZTaLUFkgHKhSUWjZ0Au+Oue5mov7SFcfd/culurweioI22KoIKCW6l7 IadbEwtXOB/DYMrbYHOUY8P02/StvkeItVAIaeAC2H5cAA5UuaxtffKglI8WWY3fyWV17/GEBqg cRzKkhnVwk1+PsH7ns1jElg85fE8oq4E1kgLyQzYQunPDU7p6/3RyrRZQrGTQSDSEgLCz4w2cTN V2YGPSZIBP9Z0yZV6iA== X-Proofpoint-GUID: g93lDSBhAnn6IzfWnUZ_St91yTxvteTl X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2026-01-11_09,2026-01-09_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 impostorscore=0 adultscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 phishscore=0 clxscore=1015 lowpriorityscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2512120000 definitions=main-2601120022 On 07/01/26 2:53 pm, Shrikanth Hegde wrote: > Hello. > > While doing some tracing, observed this kernel panic on powerpc. > > It is quite easy reproduce this. > - keep it preempt=full/lazy > - enable some bcc tools. for example: ./stackcount nohz_balance_exit_idle > - Run some workload such as "hackbench 10 process 1000 loops" > > I remember seeing this across other bcc tools. > Hello Shrikanth, Thanks for the repro steps. I am hitting this issue on the latest linux-next kernel. Regards, Venkat. > > > Seen this on tip/master: > commit 5d3b0106245d467fd5ba0bd9a373a13356684f6e (HEAD -> master, > origin/master, origin/HEAD) > Merge: 93368366738f e21279b73ef6 > Author: Ingo Molnar > Date:   Tue Jan 6 09:04:47 2026 +0100 > >     Merge branch into tip/master: 'x86/sev' > > > > Panic log: >  attempted to read user page (6b8) - exploit attempt? (uid: 0) >  BUG: Kernel NULL pointer dereference on read at 0x000006b8 >  Faulting instruction address: 0xc00000000013cf10 >  Oops: Kernel access of bad area, sig: 11 [#1] >  CPU: 38 UID: 0 PID: 2938 Comm: hackbench Kdump: loaded Not tainted > 6.19.0-rc4+ #326 PREEMPT(full) >  NIP:  c00000000013cf10 LR: c00000000013ced0 CTR: c0000000004a7f08 >  REGS: c0000000a7f96b60 TRAP: 0300   Not tainted  (6.19.0-rc4+) >  MSR:  8000000000001033   CR: 88022828 XER: 20040000 >  CFAR: c00000000050490c DAR: 00000000000006b8 DSISR: 40000000 IRQMASK: 3 >  GPR00: c00000000013ced0 c0000000a7f96e00 c000000001c38100 > 0000000000000000 >  GPR04: 00007fffda01fea8 0000000000000008 0000000000000000 > 00007fff94f05e84 >  GPR08: c0000000a7f90000 0000000000000000 00007fffda0205d0 > 0000000000004000 >  GPR12: c000000002dbdddc c0000017fd891c80 c0000000001e08f4 > 0000000000000000 >  GPR16: 0000000000000000 0000000000000000 0000000000000000 > 00000d9842ecbda0 >  GPR20: c0000000c5c54a00 0000000000000026 0000000000000000 > 0000000000000000 >  GPR24: 0000000000000001 fffffffffffffe00 c0000000c5c54a00 > 000ffffffffffff8 >  GPR28: 00007fffffffffdf 0000000000000000 00007fffda01fea0 > c0000000a7f96ef0 >  NIP [c00000000013cf10] perf_callchain_user_64+0x1b0/0x4f0 >  LR [c00000000013ced0] perf_callchain_user_64+0x170/0x4f0 >  Call Trace: >  perf_callchain_user_64+0x170/0x4f0 (unreliable) >  perf_callchain_user+0x20/0x3c >  get_perf_callchain+0x1b0/0x3dc >  bpf_get_stackid+0x94/0xec >  bpf_prog_1ca8f9c0bc38eaa6_trace_count+0x70/0x1bc >  trace_call_bpf+0x124/0x3c4 >  kprobe_perf_func+0x54/0x2f8 >  kprobe_ftrace_handler+0x1dc/0x298 >  ftrace_regs_call+0x4/0xa0 >  nohz_balance_exit_idle+0x10/0x120 >  nohz_balancer_kick+0x50/0x3e4 >  sched_tick+0x140/0x334 >  update_process_times+0xf0/0x144 >  tick_nohz_handler+0xc4/0x274 >  __hrtimer_run_queues+0x1c4/0x480 >  hrtimer_interrupt+0x12c/0x30c >  timer_interrupt+0x140/0x394 >  __replay_soft_interrupts+0xa0/0x154 >  arch_local_irq_restore.part.0+0x1ac/0x224 >  _raw_spin_unlock_irqrestore+0x50/0xa0 >  try_to_wake_up+0x3e8/0xa58 >  wake_up_q+0x88/0xe4 >  rwsem_wake.isra.0+0x98/0xd8 >  up_write+0xa8/0xb4 >  unlink_file_vma_batch_process+0xc8/0xf0 >  unlink_file_vma_batch_add+0x5c/0xa4 >  free_pgtables+0x110/0x394 >  exit_mmap+0x1a0/0x5a8 >  __mmput+0x64/0x194 >  exit_mm+0xe0/0x170 >  do_exit+0x21c/0x5d0 >  do_group_exit+0x4c/0xc0 >  pid_child_should_wake+0x0/0x7c >  system_call_exception+0x128/0x390 >  system_call_vectored_common+0x15c/0x2ec > > > > Looks like venkat had reported similar one earlier. > https://lore.kernel.org/all/49cb29fc-003c-422a-98bd-dee8f13aa0b4@linux.ibm.com/ > > > Venkat, can you give above mentioned steps a try on linux-next latest? >