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Wed, 13 Jul 2022 18:31:46 -0700 (PDT) Received: from localhost.localdomain ([85.203.23.27]) by smtp.gmail.com with ESMTPSA id r14-20020a63ec4e000000b004150a28a56fsm21912pgj.53.2022.07.13.18.31.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Jul 2022 18:31:46 -0700 (PDT) From: Zhouyi Zhou To: mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org, npiggin@gmail.com, ldufour@linux.ibm.com, pmladek@suse.com, john.ogness@linutronix.de, Julia.Lawall@inria.fr, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, lance@osuosl.org, paulmck@kernel.org, rcu@vger.kernel.org Subject: [PATCH linux-next] powerpc: use raw_smp_processor_id in arch_touch_nmi_watchdog Date: Thu, 14 Jul 2022 09:31:31 +0800 Message-Id: <20220714013131.12648-1-zhouzhouyi@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 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: Zhouyi Zhou Errors-To: linuxppc-dev-bounces+incoming=patchwork.ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" use raw_smp_processor_id() in arch_touch_nmi_watchdog because when called from watchdog, the cpu is preemptible. Signed-off-by: Zhouyi Zhou Tested-by: Zhouyi Zhou --- Dear PPC developers I found this bug when trying to do rcutorture tests in ppc VM of Open Source Lab of Oregon State University. qemu-system-ppc64 -nographic -smp cores=4,threads=1 -net none -M pseries -nodefaults -device spapr-vscsi -serial file:/tmp/console.log -m 2G -kernel /home/ubuntu/linux-next/tools/testing/selftests/rcutorture/res/2022.07.08-22.36.11-torture/results-rcuscale-kvfree/TREE/vmlinux -append "debug_boot_weak_hash panic=-1 console=ttyS0 rcuscale.kfree_rcu_test=1 rcuscale.kfree_nthreads=16 rcuscale.holdoff=20 rcuscale.kfree_loops=10000 torture.disable_onoff_at_boot rcuscale.shutdown=1 rcuscale.verbose=0" tail /tmp/console.log [ 1232.433552][ T41] BUG: using smp_processor_id() in preemptible [00000000] code: khungtaskd/41 [ 1232.439751][ T41] caller is arch_touch_nmi_watchdog+0x34/0xd0 [ 1232.440934][ T41] CPU: 3 PID: 41 Comm: khungtaskd Not tainted 5.19.0-rc5-next-20220708-dirty #106 [ 1232.442684][ T41] Call Trace: [ 1232.443343][ T41] [c0000000029cbbb0] [c0000000006df360] dump_stack_lvl+0x74/0xa8 (unreliable) [ 1232.445237][ T41] [c0000000029cbbf0] [c000000000d04f30] check_preemption_disabled+0x150/0x160 [ 1232.446926][ T41] [c0000000029cbc80] [c000000000035584] arch_touch_nmi_watchdog+0x34/0xd0 [ 1232.448532][ T41] [c0000000029cbcb0] [c0000000002068ac] watchdog+0x40c/0x5b0 [ 1232.451449][ T41] [c0000000029cbdc0] [c000000000139df4] kthread+0x144/0x170 [ 1232.452896][ T41] [c0000000029cbe10] [c00000000000cd54] ret_from_kernel_thread+0x5c/0x64 After this fix, "BUG: using smp_processor_id() in preemptible [00000000] code: khungtaskd/41" does not appear again. I also examined other places in watchdog.c where smp_processor_id() are used, but they are well protected by preempt disable. Kind Regards Zhouyi -- arch/powerpc/kernel/watchdog.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c index 7d28b9553654..ab6b84e00311 100644 --- a/arch/powerpc/kernel/watchdog.c +++ b/arch/powerpc/kernel/watchdog.c @@ -450,7 +450,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) void arch_touch_nmi_watchdog(void) { unsigned long ticks = tb_ticks_per_usec * wd_timer_period_ms * 1000; - int cpu = smp_processor_id(); + int cpu = raw_smp_processor_id(); u64 tb; if (!cpumask_test_cpu(cpu, &watchdog_cpumask))