[PATCH] x86/resctrl: Take care of PF_EXITING task in callback

[Xiaochen Shen]

When writing a pid to file "tasks", a callback function move_myself()
is queued to this task to be called when the task returns from kernel
mode or exits. The purpose of move_myself() is to activate the newly
assigned closid and/or rmid associated with this task. This activation
is done by calling resctrl_sched_in() from move_myself(), the same
function that is called when switching to this task.

If this work is successfully queued but then the task enters PF_EXITING
status (e.g., receiving signal SIGKILL, SIGTERM) prior to the execution
of the callback move_myself() then move_myself() still calls
resctrl_sched_in() since the task status is not currently considered.

When a task is exiting then the data structure of the task itself will
be freed soon, calling resctrl_sched_in() to write the register that
control's the task's resources is unnecessary and it implies extra
performance overhead.

Add check on task status in move_myself() and return immediately if the
task is PF_EXITING.

Signed-off-by: Xiaochen Shen <xiaochen.shen@xxxxxxxxx>
Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 2e3b06d6bbc6..205925d802d8 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -532,11 +532,15 @@ static void move_myself(struct callback_head *head)
 		kfree(rdtgrp);
 	}
 
+	if (unlikely(current->flags & PF_EXITING))
+		goto out;
+
 	preempt_disable();
 	/* update PQR_ASSOC MSR to make resource group go into effect */
 	resctrl_sched_in();
 	preempt_enable();
 
+out:
 	kfree(callback);
 }
 
-- 
1.8.3.1