Commit d60585c5 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Ingo Molnar
Browse files

sched/core: Correct off by one bug in load migration calculation 



The move of calc_load_migrate() from CPU_DEAD to CPU_DYING did not take into
account that the function is now called from a thread running on the outgoing
CPU. As a result a cpu unplug leakes a load of 1 into the global load
accounting mechanism.

Fix it by adjusting for the currently running thread which calls
calc_load_migrate().

Reported-by: default avatarAnton Blanchard <anton@samba.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Cc: rt@linutronix.de
Cc: shreyas@linux.vnet.ibm.com
Fixes: e9cd8fa4: ("sched/migration: Move calc_load_migrate() into CPU_DYING")
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1607121744350.4083@nanos


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 92d21ac7

kernel/sched/core.c

+4 −2
Original line number Diff line number Diff line
@@ -5394,13 +5394,15 @@ void idle_task_exit(void) 
/*

 * Since this CPU is going 'away' for a while, fold any nr_active delta

 * we might have. Assumes we're called after migrate_tasks() so that the

 * nr_active count is stable.

 * nr_active count is stable. We need to take the teardown thread which

 * is calling this into account, so we hand in adjust = 1 to the load

 * calculation.

 *

 * Also see the comment "Global load-average calculations".

 */

static void calc_load_migrate(struct rq *rq)

{

	long delta = calc_load_fold_active(rq);

	long delta = calc_load_fold_active(rq, 1);

	if (delta)

		atomic_long_add(delta, &calc_load_tasks);

}

kernel/sched/loadavg.c

+4 −4
Original line number Diff line number Diff line
@@ -78,11 +78,11 @@ void get_avenrun(unsigned long *loads, unsigned long offset, int shift) 
	loads[2] = (avenrun[2] + offset) << shift;

}



long calc_load_fold_active(struct rq *this_rq)

long calc_load_fold_active(struct rq *this_rq, long adjust)

{

	long nr_active, delta = 0;



	nr_active = this_rq->nr_running;

	nr_active = this_rq->nr_running - adjust;

	nr_active += (long)this_rq->nr_uninterruptible;



	if (nr_active != this_rq->calc_load_active) {
@@ -188,7 +188,7 @@ void calc_load_enter_idle(void) 
	 * We're going into NOHZ mode, if there's any pending delta, fold it

	 * into the pending idle delta.

	 */

	delta = calc_load_fold_active(this_rq);

	delta = calc_load_fold_active(this_rq, 0);

	if (delta) {

		int idx = calc_load_write_idx();
@@ -389,7 +389,7 @@ void calc_global_load_tick(struct rq *this_rq) 
	if (time_before(jiffies, this_rq->calc_load_update))

		return;



	delta  = calc_load_fold_active(this_rq);

	delta  = calc_load_fold_active(this_rq, 0);

	if (delta)

		atomic_long_add(delta, &calc_load_tasks);

kernel/sched/sched.h

+1 −1
Original line number Diff line number Diff line
@@ -28,7 +28,7 @@ extern unsigned long calc_load_update; 
extern atomic_long_t calc_load_tasks;



extern void calc_global_load_tick(struct rq *this_rq);

extern long calc_load_fold_active(struct rq *this_rq);

extern long calc_load_fold_active(struct rq *this_rq, long adjust);



#ifdef CONFIG_SMP

extern void cpu_load_update_active(struct rq *this_rq);

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