From: Reinette Chatre Date: Thu, 17 Dec 2020 22:31:20 +0000 (-0800) Subject: x86/resctrl: Use task_curr() instead of task_struct->on_cpu to prevent unnecessary IPI X-Git-Tag: accepted/tizen/unified/20230118.172025~7882^2~1 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=e0ad6dc8969f790f14bddcfd7ea284b7e5f88a16;p=platform%2Fkernel%2Flinux-rpi.git x86/resctrl: Use task_curr() instead of task_struct->on_cpu to prevent unnecessary IPI James reported in [1] that there could be two tasks running on the same CPU with task_struct->on_cpu set. Using task_struct->on_cpu as a test if a task is running on a CPU may thus match the old task for a CPU while the scheduler is running and IPI it unnecessarily. task_curr() is the correct helper to use. While doing so move the #ifdef check of the CONFIG_SMP symbol to be a C conditional used to determine if this helper should be used to ensure the code is always checked for correctness by the compiler. [1] https://lore.kernel.org/lkml/a782d2f3-d2f6-795f-f4b1-9462205fd581@arm.com Reported-by: James Morse Signed-off-by: Reinette Chatre Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/e9e68ce1441a73401e08b641cc3b9a3cf13fe6d4.1608243147.git.reinette.chatre@intel.com --- diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c index 460f3e0..37f37df 100644 --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c @@ -2313,19 +2313,15 @@ static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to, t->closid = to->closid; t->rmid = to->mon.rmid; -#ifdef CONFIG_SMP /* - * This is safe on x86 w/o barriers as the ordering - * of writing to task_cpu() and t->on_cpu is - * reverse to the reading here. The detection is - * inaccurate as tasks might move or schedule - * before the smp function call takes place. In - * such a case the function call is pointless, but + * If the task is on a CPU, set the CPU in the mask. + * The detection is inaccurate as tasks might move or + * schedule before the smp function call takes place. + * In such a case the function call is pointless, but * there is no other side effect. */ - if (mask && t->on_cpu) + if (IS_ENABLED(CONFIG_SMP) && mask && task_curr(t)) cpumask_set_cpu(task_cpu(t), mask); -#endif } } read_unlock(&tasklist_lock);