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authorTejun Heo <tj@kernel.org>2015-12-08 11:28:04 -0500
committerTejun Heo <tj@kernel.org>2015-12-08 11:29:47 -0500
commit82607adcf9cdf40fb7b5331269780c8f70ec6e35 (patch)
tree22c7849ef8e873007dd56a63b109937046d897db /kernel/workqueue.c
parent03e0d4610bf4d4a93bfa16b2474ed4fd5243aa71 (diff)
downloadlinux-sh-82607adcf9cdf40fb7b5331269780c8f70ec6e35.tar.gz
workqueue: implement lockup detector
Workqueue stalls can happen from a variety of usage bugs such as missing WQ_MEM_RECLAIM flag or concurrency managed work item indefinitely staying RUNNING. These stalls can be extremely difficult to hunt down because the usual warning mechanisms can't detect workqueue stalls and the internal state is pretty opaque. To alleviate the situation, this patch implements workqueue lockup detector. It periodically monitors all worker_pools periodically and, if any pool failed to make forward progress longer than the threshold duration, triggers warning and dumps workqueue state as follows. BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 31s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=17/256 pending: monkey_wrench_fn, e1000_watchdog, cache_reap, vmstat_shepherd, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, release_one_tty, cgroup_release_agent workqueue events_power_efficient: flags=0x80 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 pending: check_lifetime, neigh_periodic_work workqueue cgroup_pidlist_destroy: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 pending: cgroup_pidlist_destroy_work_fn ... The detection mechanism is controller through kernel parameter workqueue.watchdog_thresh and can be updated at runtime through the sysfs module parameter file. v2: Decoupled from softlockup control knobs. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Chris Mason <clm@fb.com> Cc: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'kernel/workqueue.c')
-rw-r--r--kernel/workqueue.c174
1 files changed, 171 insertions, 3 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c7769c507bf5..1ecb588aae07 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -148,6 +148,8 @@ struct worker_pool {
int id; /* I: pool ID */
unsigned int flags; /* X: flags */
+ unsigned long watchdog_ts; /* L: watchdog timestamp */
+
struct list_head worklist; /* L: list of pending works */
int nr_workers; /* L: total number of workers */
@@ -1083,6 +1085,8 @@ static void pwq_activate_delayed_work(struct work_struct *work)
struct pool_workqueue *pwq = get_work_pwq(work);
trace_workqueue_activate_work(work);
+ if (list_empty(&pwq->pool->worklist))
+ pwq->pool->watchdog_ts = jiffies;
move_linked_works(work, &pwq->pool->worklist, NULL);
__clear_bit(WORK_STRUCT_DELAYED_BIT, work_data_bits(work));
pwq->nr_active++;
@@ -1385,6 +1389,8 @@ retry:
trace_workqueue_activate_work(work);
pwq->nr_active++;
worklist = &pwq->pool->worklist;
+ if (list_empty(worklist))
+ pwq->pool->watchdog_ts = jiffies;
} else {
work_flags |= WORK_STRUCT_DELAYED;
worklist = &pwq->delayed_works;
@@ -2157,6 +2163,8 @@ recheck:
list_first_entry(&pool->worklist,
struct work_struct, entry);
+ pool->watchdog_ts = jiffies;
+
if (likely(!(*work_data_bits(work) & WORK_STRUCT_LINKED))) {
/* optimization path, not strictly necessary */
process_one_work(worker, work);
@@ -2240,6 +2248,7 @@ repeat:
struct pool_workqueue, mayday_node);
struct worker_pool *pool = pwq->pool;
struct work_struct *work, *n;
+ bool first = true;
__set_current_state(TASK_RUNNING);
list_del_init(&pwq->mayday_node);
@@ -2256,9 +2265,14 @@ repeat:
* process'em.
*/
WARN_ON_ONCE(!list_empty(scheduled));
- list_for_each_entry_safe(work, n, &pool->worklist, entry)
- if (get_work_pwq(work) == pwq)
+ list_for_each_entry_safe(work, n, &pool->worklist, entry) {
+ if (get_work_pwq(work) == pwq) {
+ if (first)
+ pool->watchdog_ts = jiffies;
move_linked_works(work, scheduled, &n);
+ }
+ first = false;
+ }
if (!list_empty(scheduled)) {
process_scheduled_works(rescuer);
@@ -3104,6 +3118,7 @@ static int init_worker_pool(struct worker_pool *pool)
pool->cpu = -1;
pool->node = NUMA_NO_NODE;
pool->flags |= POOL_DISASSOCIATED;
+ pool->watchdog_ts = jiffies;
INIT_LIST_HEAD(&pool->worklist);
INIT_LIST_HEAD(&pool->idle_list);
hash_init(pool->busy_hash);
@@ -4343,7 +4358,9 @@ void show_workqueue_state(void)
pr_info("pool %d:", pool->id);
pr_cont_pool_info(pool);
- pr_cont(" workers=%d", pool->nr_workers);
+ pr_cont(" hung=%us workers=%d",
+ jiffies_to_msecs(jiffies - pool->watchdog_ts) / 1000,
+ pool->nr_workers);
if (pool->manager)
pr_cont(" manager: %d",
task_pid_nr(pool->manager->task));
@@ -5202,6 +5219,154 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq)
static void workqueue_sysfs_unregister(struct workqueue_struct *wq) { }
#endif /* CONFIG_SYSFS */
+/*
+ * Workqueue watchdog.
+ *
+ * Stall may be caused by various bugs - missing WQ_MEM_RECLAIM, illegal
+ * flush dependency, a concurrency managed work item which stays RUNNING
+ * indefinitely. Workqueue stalls can be very difficult to debug as the
+ * usual warning mechanisms don't trigger and internal workqueue state is
+ * largely opaque.
+ *
+ * Workqueue watchdog monitors all worker pools periodically and dumps
+ * state if some pools failed to make forward progress for a while where
+ * forward progress is defined as the first item on ->worklist changing.
+ *
+ * This mechanism is controlled through the kernel parameter
+ * "workqueue.watchdog_thresh" which can be updated at runtime through the
+ * corresponding sysfs parameter file.
+ */
+#ifdef CONFIG_WQ_WATCHDOG
+
+static void wq_watchdog_timer_fn(unsigned long data);
+
+static unsigned long wq_watchdog_thresh = 30;
+static struct timer_list wq_watchdog_timer =
+ TIMER_DEFERRED_INITIALIZER(wq_watchdog_timer_fn, 0, 0);
+
+static unsigned long wq_watchdog_touched = INITIAL_JIFFIES;
+static DEFINE_PER_CPU(unsigned long, wq_watchdog_touched_cpu) = INITIAL_JIFFIES;
+
+static void wq_watchdog_reset_touched(void)
+{
+ int cpu;
+
+ wq_watchdog_touched = jiffies;
+ for_each_possible_cpu(cpu)
+ per_cpu(wq_watchdog_touched_cpu, cpu) = jiffies;
+}
+
+static void wq_watchdog_timer_fn(unsigned long data)
+{
+ unsigned long thresh = READ_ONCE(wq_watchdog_thresh) * HZ;
+ bool lockup_detected = false;
+ struct worker_pool *pool;
+ int pi;
+
+ if (!thresh)
+ return;
+
+ rcu_read_lock();
+
+ for_each_pool(pool, pi) {
+ unsigned long pool_ts, touched, ts;
+
+ if (list_empty(&pool->worklist))
+ continue;
+
+ /* get the latest of pool and touched timestamps */
+ pool_ts = READ_ONCE(pool->watchdog_ts);
+ touched = READ_ONCE(wq_watchdog_touched);
+
+ if (time_after(pool_ts, touched))
+ ts = pool_ts;
+ else
+ ts = touched;
+
+ if (pool->cpu >= 0) {
+ unsigned long cpu_touched =
+ READ_ONCE(per_cpu(wq_watchdog_touched_cpu,
+ pool->cpu));
+ if (time_after(cpu_touched, ts))
+ ts = cpu_touched;
+ }
+
+ /* did we stall? */
+ if (time_after(jiffies, ts + thresh)) {
+ lockup_detected = true;
+ pr_emerg("BUG: workqueue lockup - pool");
+ pr_cont_pool_info(pool);
+ pr_cont(" stuck for %us!\n",
+ jiffies_to_msecs(jiffies - pool_ts) / 1000);
+ }
+ }
+
+ rcu_read_unlock();
+
+ if (lockup_detected)
+ show_workqueue_state();
+
+ wq_watchdog_reset_touched();
+ mod_timer(&wq_watchdog_timer, jiffies + thresh);
+}
+
+void wq_watchdog_touch(int cpu)
+{
+ if (cpu >= 0)
+ per_cpu(wq_watchdog_touched_cpu, cpu) = jiffies;
+ else
+ wq_watchdog_touched = jiffies;
+}
+
+static void wq_watchdog_set_thresh(unsigned long thresh)
+{
+ wq_watchdog_thresh = 0;
+ del_timer_sync(&wq_watchdog_timer);
+
+ if (thresh) {
+ wq_watchdog_thresh = thresh;
+ wq_watchdog_reset_touched();
+ mod_timer(&wq_watchdog_timer, jiffies + thresh * HZ);
+ }
+}
+
+static int wq_watchdog_param_set_thresh(const char *val,
+ const struct kernel_param *kp)
+{
+ unsigned long thresh;
+ int ret;
+
+ ret = kstrtoul(val, 0, &thresh);
+ if (ret)
+ return ret;
+
+ if (system_wq)
+ wq_watchdog_set_thresh(thresh);
+ else
+ wq_watchdog_thresh = thresh;
+
+ return 0;
+}
+
+static const struct kernel_param_ops wq_watchdog_thresh_ops = {
+ .set = wq_watchdog_param_set_thresh,
+ .get = param_get_ulong,
+};
+
+module_param_cb(watchdog_thresh, &wq_watchdog_thresh_ops, &wq_watchdog_thresh,
+ 0644);
+
+static void wq_watchdog_init(void)
+{
+ wq_watchdog_set_thresh(wq_watchdog_thresh);
+}
+
+#else /* CONFIG_WQ_WATCHDOG */
+
+static inline void wq_watchdog_init(void) { }
+
+#endif /* CONFIG_WQ_WATCHDOG */
+
static void __init wq_numa_init(void)
{
cpumask_var_t *tbl;
@@ -5325,6 +5490,9 @@ static int __init init_workqueues(void)
!system_unbound_wq || !system_freezable_wq ||
!system_power_efficient_wq ||
!system_freezable_power_efficient_wq);
+
+ wq_watchdog_init();
+
return 0;
}
early_initcall(init_workqueues);