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Fri, 24 Oct 2025 14:58:56 GMT Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A59B320049; Fri, 24 Oct 2025 14:58:56 +0000 (GMT) Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 611522004D; Fri, 24 Oct 2025 14:58:56 +0000 (GMT) Received: from tuxmaker.lnxne.boe (unknown [9.152.85.9]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 24 Oct 2025 14:58:56 +0000 (GMT) From: Jan Polensky To: peterz@infradead.org Cc: arighi@nvidia.com, bsegall@google.com, cgroups@vger.kernel.org, changwoo@igalia.com, dietmar.eggemann@arm.com, hannes@cmpxchg.org, juri.lelli@redhat.com, linux-kernel@vger.kernel.org, liuwenfang@honor.com, longman@redhat.com, mgorman@suse.de, mingo@kernel.org, mkoutny@suse.com, rostedt@goodmis.org, sched-ext@lists.linux.dev, tglx@linutronix.de, tj@kernel.org, vincent.guittot@linaro.org, void@manifault.com, vschneid@redhat.com Subject: [REGRESSION] Deadlock during CPU hotplug caused by abfc01077df6 Date: Fri, 24 Oct 2025 16:58:13 +0200 Message-ID: <20251024145813.3535989-1-japo@linux.ibm.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20251006104527.331463972@infradead.org> References: <20251006104527.331463972@infradead.org> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMDE4MDAyMiBTYWx0ZWRfX1lG0d+9jWs2i qjW+YL88euygrb/TDxHflBUsITHkXldfkSdl+NmpWHgDVVC5I7yJWq+G8H8qRlf7Xh9SpwcaBQS yaGl9hoQFhMc/ZXvx6OqYIgPmuR6+p+4ZBDat8fJ6I+I+/Wtc5l7kKf+xOEmOyMcmBVmeAnQCH/ F9abKagwY1ka6KrAhjIupLutCMEzYQT/PcKe359kLNUFrwAyseixq1kWn0VlQ26KHGENP21MGAr s3PhUSG8jT8FTh4fRYo6hE/HhrHhv08NKNnQhL1mhMw8N45fZbELisTflh+84E1jN4bH8Gsb0AV fmmYep/yttoFtdx/BKjomze+s/ClDMSuQzuPUOq0EiV/gfsbv8dW3M/y1PMfhT1LjMQarnzm3hx 2sKbFXImc/wf24HfYDkAHQl0v89rEg== X-Authority-Analysis: v=2.4 cv=OrVCCi/t c=1 sm=1 tr=0 ts=68fb9434 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=x6icFKpwvdMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=URV6e8FYp2escMi8J3AA:9 a=nl4s5V0KI7Kw-pW0DWrs:22 a=pHzHmUro8NiASowvMSCR:22 a=xoEH_sTeL_Rfw54TyV31:22 X-Proofpoint-GUID: NpgHxX1xjup5R5nTAXr8ZAdnZjBDxJY6 X-Proofpoint-ORIG-GUID: -0TDq8IPZJWfnl-VYFVFqWZReKs3ooxm X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-10-24_02,2025-10-22_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 adultscore=0 priorityscore=1501 spamscore=0 phishscore=0 clxscore=1011 bulkscore=0 malwarescore=0 lowpriorityscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510020000 definitions=main-2510180022 We've identified a regression introduced by commit abfc01077df6 ("sched: Fix do_set_cpus_allowed() locking") that causes a reproducible deadlock during CPU hotplug testing on s390x. While running the cpuhotplug02.sh test from LTP, which dynamically offlines and onlines CPUs, the system consistently enters a stalled state. Observed behavior: - migration/N attempts to migrate a task currently executing on another CPU. - Concurrently, rcu_sched tries to complete an RCU grace period. - Both threads are blocked on spinlocks (e.g., arch_spin_lock_wait), likely due to lock contention. - Neither thread progresses; the grace period stalls. - The kernel detects the stall and triggers a crash dump. Sys info: RELEASE: 6.18.0-20251021.rc2.git224.fe45352cd106.63.fc42.s390x+next CPUS: 32 TASKS: 623 MEMORY: 16 GB Crash log excerpt: [ 6146.992159] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [ 6146.992173] rcu: 1-...0: (5 ticks this GP) idle=cea4/1/0x4000000000000000 softirq=1055899/1055901 fqs=4769 [ 6146.992236] rcu: (detected by 3, t=240013 jiffies, g=2041729, q=14778 ncpus=32) [ 6146.992240] Task dump for CPU 1: [ 6146.992241] task:migration/1 state:R running task stack:0 pid:22 tgid:22 ppid:2 task_flags:0x4208040 flags:0x00000000 [ 6146.992246] Stopper: __balance_push_cpu_stop+0x0/0x230 <- balance_push+0xea/0x170 [ 6146.992254] Call Trace: [ 6146.992255] [<000000009d9e2300>] 0x9d9e2300 [ 6146.992280] rcu: rcu_sched kthread starved for 210010 jiffies! g2041729 f0x2 RCU_GP_DOING_FQS(6) ->state=0x0 ->cpu=23 [ 6146.992287] rcu: Unless rcu_sched kthread gets sufficient CPU time, OOM is now expected behavior. [ 6146.992288] rcu: RCU grace-period kthread stack dump: [ 6146.992289] task:rcu_sched state:R running task stack:0 pid:16 tgid:16 ppid:2 task_flags:0x208040 flags:0x00000010 [ 6146.992294] Call Trace: [ 6146.992295] [<0700000000000001>] 0x700000000000001 [ 6146.992298] [<000002e1fb072998>] arch_spin_lock_wait+0xc8/0x110 [ 6146.992303] [<000002e1fa239d06>] raw_spin_rq_lock_nested+0x96/0xc0 [ 6146.992306] [<000002e1fa23bc90>] resched_cpu+0x50/0xc0 [ 6146.992309] [<000002e1fa29d646>] force_qs_rnp+0x306/0x3e0 [ 6146.992314] [<000002e1fa29ed30>] rcu_gp_fqs_loop+0x430/0x6e0 [ 6146.992316] [<000002e1fa2a1b0e>] rcu_gp_kthread+0x1ee/0x270 [ 6146.992320] [<000002e1fa228edc>] kthread+0x12c/0x250 [ 6146.992323] [<000002e1fa19ccfc>] __ret_from_fork+0x3c/0x150 [ 6146.992328] [<000002e1fb0800ba>] ret_from_fork+0xa/0x30