The following bug was triggered on a system built with CONFIG_DEBUG_PREEMPT=y: # echo p > /proc/sysrq-trigger BUG: using smp_processor_id() in preemptible [00000000] code: sh/117 caller is perf_event_print_debug+0x1a/0x4c0 CPU: 3 UID: 0 PID: 117 Comm: sh Not tainted 6.11.0-rc1 #109 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x4f/0x60 check_preemption_disabled+0xc8/0xd0 perf_event_print_debug+0x1a/0x4c0 __handle_sysrq+0x140/0x180 write_sysrq_trigger+0x61/0x70 proc_reg_write+0x4e/0x70 vfs_write+0xd0/0x430 ? handle_mm_fault+0xc8/0x240 ksys_write+0x9c/0xd0 do_syscall_64+0x96/0x190 entry_SYSCALL_64_after_hwframe+0x4b/0x53 This is because the commit d4b294bf84db ("perf/x86: Hybrid PMU support for counters") took smp_processor_id() outside the irq critical section. If a preemption occurs in perf_event_print_debug() and the task is migrated to another cpu, we may get incorrect pmu debug information. Move smp_processor_id() back inside the irq critical section to fix this issue. Fixes: d4b294bf84db ("perf/x86: Hybrid PMU support for counters") Signed-off-by: Li Huafei <lihuafei1@huawei.com> Reviewed-and-tested-by: K Prateek Nayak <kprateek.nayak@amd.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Kan Liang <kan.liang@linux.intel.com> Link: https://lore.kernel.org/r/20240729220928.325449-1-lihuafei1@huawei.com