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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: Anton Blanchard <anton@samba.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter 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: e9cd8fa4fcfd: ("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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Thomas Gleixner 2016-07-12 18:33:56 +02:00 committed by Ingo Molnar
parent 92d21ac74a
commit d60585c576
3 changed files with 9 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
kernel/sched/core.c
View File

@ -5394,13 +5394,15 @@ void idle_task_exit(void)
/* /*
* Since this CPU is going 'away' for a while, fold any nr_active delta * 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 * 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". * Also see the comment "Global load-average calculations".
*/ */
static void calc_load_migrate(struct rq *rq) 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) if (delta)
atomic_long_add(delta, &calc_load_tasks); atomic_long_add(delta, &calc_load_tasks);
} }

8
kernel/sched/loadavg.c
View File

@ -78,11 +78,11 @@ void get_avenrun(unsigned long *loads, unsigned long offset, int shift)
loads[2] = (avenrun[2] + offset) << 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; 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; nr_active += (long)this_rq->nr_uninterruptible;
if (nr_active != this_rq->calc_load_active) { 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 * We're going into NOHZ mode, if there's any pending delta, fold it
* into the pending idle delta. * into the pending idle delta.
*/ */
delta = calc_load_fold_active(this_rq); delta = calc_load_fold_active(this_rq, 0);
if (delta) { if (delta) {
int idx = calc_load_write_idx(); 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)) if (time_before(jiffies, this_rq->calc_load_update))
return; return;
delta = calc_load_fold_active(this_rq); delta = calc_load_fold_active(this_rq, 0);
if (delta) if (delta)
atomic_long_add(delta, &calc_load_tasks); atomic_long_add(delta, &calc_load_tasks);

2
kernel/sched/sched.h
View File

@ -28,7 +28,7 @@ extern unsigned long calc_load_update;
extern atomic_long_t calc_load_tasks; extern atomic_long_t calc_load_tasks;
extern void calc_global_load_tick(struct rq *this_rq); 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 #ifdef CONFIG_SMP
extern void cpu_load_update_active(struct rq *this_rq); extern void cpu_load_update_active(struct rq *this_rq);