DEBUG_PREEMPT complains about using this_cpu_ptr() in preemptible: BUG: using smp_processor_id() in preemptible [00000000] code: iperf-300s-cs-l/277 caller is debug_smp_processor_id+0x17/0x19 CPU: 1 PID: 277 Comm: iperf-300s-cs-l Not tainted 4.9.0-rc8-00140-gcc639db #2 ffffc900003f3cf0 ffffffff8123ae6f 0000000000000001 ffffffff818181da ffffc900003f3d20 ffffffff81252f41 0000000000012de0 00000000fffffdff ffff880009328f40 ffff88000592c400 ffffc900003f3d30 ffffffff81252f6a Call Trace: [<ffffffff8123ae6f>] dump_stack+0x9a/0xd0 [<ffffffff81252f41>] check_preemption_disabled+0xdd/0xef [<ffffffff81252f6a>] debug_smp_processor_id+0x17/0x19 [<ffffffff811796df>] __vfree_deferred+0x16/0x4c [<ffffffff8117b584>] vfree_atomic+0x22/0x24 [<ffffffff81094f5d>] free_thread_stack+0xc2/0x106 [<ffffffff810951be>] put_task_stack+0x4c/0x62 [<ffffffff81095f81>] copy_process+0x7e0/0x16e8 [<ffffffff8109702d>] _do_fork+0xbb/0x2d3 [<ffffffff810465e8>] ? __do_page_fault+0x2e1/0x384 [<ffffffff8112633f>] ? trace_hardirqs_off_caller+0x12/0x24 [<ffffffff810972cb>] SyS_clone+0x19/0x1b [<ffffffff81003800>] do_syscall_64+0x143/0x173 [<ffffffff81507289>] entry_SYSCALL64_slow_path+0x25/0x25
Use raw_cpu_ptr() instead of this_cpu_ptr() to hide this warning. It's fine because llist_add() implementation is lock-less, so it works even if we adding to the list of some other cpu. schedule_work() is also preempt-safe. Reported-by: kernel test robot <ying.hu...@linux.intel.com> Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com> --- mm/vmalloc.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 43f0608..d8813963 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1498,7 +1498,14 @@ static void __vunmap(const void *addr, int deallocate_pages) static inline void __vfree_deferred(const void *addr) { - struct vfree_deferred *p = this_cpu_ptr(&vfree_deferred); + /* + * Use raw_cpu_ptr() because this can be called from preemptible + * context. Preemption is absolutely fine here, because llist_add() + * implementation is lockless, so it works even if we adding to list + * of the other cpu. + * schedule_work() should be fine with this too. + */ + struct vfree_deferred *p = raw_cpu_ptr(&vfree_deferred); if (llist_add((struct llist_node *)addr, &p->list)) schedule_work(&p->wq); -- 2.7.3