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workqueue: Fix queue_work_on() with BH workqueues 

When queue_work_on() is used to queue a BH work item on a remote CPU, the
work item is queued on that CPU but kick_pool() raises softirq on the local
CPU. This leads to stalls as the work item won't be executed until something
else on the remote CPU schedules a BH work item or tasklet locally.

Fix it by bouncing raising softirq to the target CPU using per-cpu irq_work.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 4cb1ef6460 ("workqueue: Implement BH workqueues to eventually replace tasklets")
This commit is contained in:
Tejun Heo 2024-02-14 08:33:55 -10:00
parent bf52b1ac6a
commit 2f34d7337d
1 changed files with 36 additions and 5 deletions
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41
kernel/workqueue.c
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@ -54,6 +54,7 @@
#include <linux/nmi.h>
#include <linux/kvm_para.h>
#include <linux/delay.h>
#include <linux/irq_work.h>
#include "workqueue_internal.h"
@ -457,6 +458,10 @@ static bool wq_debug_force_rr_cpu = false;
#endif
module_param_named(debug_force_rr_cpu, wq_debug_force_rr_cpu, bool, 0644);
/* to raise softirq for the BH worker pools on other CPUs */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct irq_work [NR_STD_WORKER_POOLS],
bh_pool_irq_works);
/* the BH worker pools */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
bh_worker_pools);
@ -1197,6 +1202,13 @@ static bool assign_work(struct work_struct *work, struct worker *worker,
return true;
}
static struct irq_work *bh_pool_irq_work(struct worker_pool *pool)
{
int high = pool->attrs->nice == HIGHPRI_NICE_LEVEL ? 1 : 0;
return &per_cpu(bh_pool_irq_works, pool->cpu)[high];
}
/**
* kick_pool - wake up an idle worker if necessary
* @pool: pool to kick
@ -1215,10 +1227,15 @@ static bool kick_pool(struct worker_pool *pool)
return false;
if (pool->flags & POOL_BH) {
if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
raise_softirq_irqoff(HI_SOFTIRQ);
else
raise_softirq_irqoff(TASKLET_SOFTIRQ);
if (likely(pool->cpu == smp_processor_id())) {
if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
raise_softirq_irqoff(HI_SOFTIRQ);
else
raise_softirq_irqoff(TASKLET_SOFTIRQ);
} else {
irq_work_queue_on(bh_pool_irq_work(pool), pool->cpu);
}
return true;
}
@ -7367,6 +7384,16 @@ static inline void wq_watchdog_init(void) { }
#endif /* CONFIG_WQ_WATCHDOG */
static void bh_pool_kick_normal(struct irq_work *irq_work)
{
raise_softirq_irqoff(TASKLET_SOFTIRQ);
}
static void bh_pool_kick_highpri(struct irq_work *irq_work)
{
raise_softirq_irqoff(HI_SOFTIRQ);
}
static void __init restrict_unbound_cpumask(const char *name, const struct cpumask *mask)
{
if (!cpumask_intersects(wq_unbound_cpumask, mask)) {
@ -7408,6 +7435,8 @@ void __init workqueue_init_early(void)
{
struct wq_pod_type *pt = &wq_pod_types[WQ_AFFN_SYSTEM];
int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL };
void (*irq_work_fns[2])(struct irq_work *) = { bh_pool_kick_normal,
bh_pool_kick_highpri };
int i, cpu;
BUILD_BUG_ON(__alignof__(struct pool_workqueue) < __alignof__(long long));
@ -7455,8 +7484,10 @@ void __init workqueue_init_early(void)
i = 0;
for_each_bh_worker_pool(pool, cpu) {
init_cpu_worker_pool(pool, cpu, std_nice[i++]);
init_cpu_worker_pool(pool, cpu, std_nice[i]);
pool->flags |= POOL_BH;
init_irq_work(bh_pool_irq_work(pool), irq_work_fns[i]);
i++;
}
i = 0;