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Merge branch 'for-4.5' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq

Browse source 
Pull workqueue update from Tejun Heo:
 "Workqueue changes for v4.5.  One cleanup patch and three to improve
  the debuggability.

  Workqueue now has a stall detector which dumps workqueue state if any
  worker pool hasn't made forward progress over a certain amount of time
  (30s by default) and also triggers a warning if a workqueue which can
  be used in memory reclaim path tries to wait on something which can't
  be.

  These should make workqueue hangs a lot easier to debug."

* 'for-4.5' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
  workqueue: simplify the apply_workqueue_attrs_locked()
  workqueue: implement lockup detector
  watchdog: introduce touch_softlockup_watchdog_sched()
  workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue
This commit is contained in:
Linus Torvalds 2016-01-11 18:53:13 -08:00
commit 0f8c790103
8 changed files with 261 additions and 15 deletions
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9
Documentation/kernel-parameters.txt
View file

@ -4140,6 +4140,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
or other driver-specific files in the
Documentation/watchdog/ directory.
workqueue.watchdog_thresh=
If CONFIG_WQ_WATCHDOG is configured, workqueue can
warn stall conditions and dump internal state to
help debugging. 0 disables workqueue stall
detection; otherwise, it's the stall threshold
duration in seconds. The default value is 30 and
it can be updated at runtime by writing to the
corresponding sysfs file.
workqueue.disable_numa
By default, all work items queued to unbound
workqueues are affine to the NUMA nodes they're

4
include/linux/sched.h
View file

@ -377,6 +377,7 @@ extern void scheduler_tick(void);
extern void sched_show_task(struct task_struct *p);
#ifdef CONFIG_LOCKUP_DETECTOR
extern void touch_softlockup_watchdog_sched(void);
extern void touch_softlockup_watchdog(void);
extern void touch_softlockup_watchdog_sync(void);
extern void touch_all_softlockup_watchdogs(void);
@ -387,6 +388,9 @@ extern unsigned int softlockup_panic;
extern unsigned int hardlockup_panic;
void lockup_detector_init(void);
#else
static inline void touch_softlockup_watchdog_sched(void)
{
}
static inline void touch_softlockup_watchdog(void)
{
}

6
include/linux/workqueue.h
View file

@ -618,4 +618,10 @@ static inline int workqueue_sysfs_register(struct workqueue_struct *wq)
{ return 0; }
#endif /* CONFIG_SYSFS */
#ifdef CONFIG_WQ_WATCHDOG
void wq_watchdog_touch(int cpu);
#else /* CONFIG_WQ_WATCHDOG */
static inline void wq_watchdog_touch(int cpu) { }
#endif /* CONFIG_WQ_WATCHDOG */
#endif

2
kernel/sched/clock.c
View file

@ -354,7 +354,7 @@ void sched_clock_idle_wakeup_event(u64 delta_ns)
return;
sched_clock_tick();
touch_softlockup_watchdog();
touch_softlockup_watchdog_sched();
}
EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);

6
kernel/time/tick-sched.c
View file

@ -143,7 +143,7 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
* when we go busy again does not account too much ticks.
*/
if (ts->tick_stopped) {
touch_softlockup_watchdog();
touch_softlockup_watchdog_sched();
if (is_idle_task(current))
ts->idle_jiffies++;
}
@ -430,7 +430,7 @@ static void tick_nohz_update_jiffies(ktime_t now)
tick_do_update_jiffies64(now);
local_irq_restore(flags);
touch_softlockup_watchdog();
touch_softlockup_watchdog_sched();
}
/*
@ -717,7 +717,7 @@ static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now, int
update_cpu_load_nohz(active);
calc_load_exit_idle();
touch_softlockup_watchdog();
touch_softlockup_watchdog_sched();
/*
* Cancel the scheduled timer and restore the tick
*/

18
kernel/watchdog.c
View file

@ -20,6 +20,7 @@
#include <linux/smpboot.h>
#include <linux/sched/rt.h>
#include <linux/tick.h>
#include <linux/workqueue.h>
#include <asm/irq_regs.h>
#include <linux/kvm_para.h>
@ -225,7 +226,15 @@ static void __touch_watchdog(void)
__this_cpu_write(watchdog_touch_ts, get_timestamp());
}
void touch_softlockup_watchdog(void)
/**
* touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
*
* Call when the scheduler may have stalled for legitimate reasons
* preventing the watchdog task from executing - e.g. the scheduler
* entering idle state. This should only be used for scheduler events.
* Use touch_softlockup_watchdog() for everything else.
*/
void touch_softlockup_watchdog_sched(void)
{
/*
* Preemption can be enabled. It doesn't matter which CPU's timestamp
@ -233,6 +242,12 @@ void touch_softlockup_watchdog(void)
*/
raw_cpu_write(watchdog_touch_ts, 0);
}
void touch_softlockup_watchdog(void)
{
touch_softlockup_watchdog_sched();
wq_watchdog_touch(raw_smp_processor_id());
}
EXPORT_SYMBOL(touch_softlockup_watchdog);
void touch_all_softlockup_watchdogs(void)
@ -246,6 +261,7 @@ void touch_all_softlockup_watchdogs(void)
*/
for_each_watchdog_cpu(cpu)
per_cpu(watchdog_touch_ts, cpu) = 0;
wq_watchdog_touch(-1);
}
#ifdef CONFIG_HARDLOCKUP_DETECTOR

220
kernel/workqueue.c
View file

@ -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 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
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 @@ static int worker_thread(void *__worker)
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 @@ static int rescuer_thread(void *__rescuer)
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 @@ static int rescuer_thread(void *__rescuer)
* 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);
@ -2316,6 +2330,37 @@ static int rescuer_thread(void *__rescuer)
goto repeat;
}
/**
* check_flush_dependency - check for flush dependency sanity
* @target_wq: workqueue being flushed
* @target_work: work item being flushed (NULL for workqueue flushes)
*
* %current is trying to flush the whole @target_wq or @target_work on it.
* If @target_wq doesn't have %WQ_MEM_RECLAIM, verify that %current is not
* reclaiming memory or running on a workqueue which doesn't have
* %WQ_MEM_RECLAIM as that can break forward-progress guarantee leading to
* a deadlock.
*/
static void check_flush_dependency(struct workqueue_struct *target_wq,
struct work_struct *target_work)
{
work_func_t target_func = target_work ? target_work->func : NULL;
struct worker *worker;
if (target_wq->flags & WQ_MEM_RECLAIM)
return;
worker = current_wq_worker();
WARN_ONCE(current->flags & PF_MEMALLOC,
"workqueue: PF_MEMALLOC task %d(%s) is flushing !WQ_MEM_RECLAIM %s:%pf",
current->pid, current->comm, target_wq->name, target_func);
WARN_ONCE(worker && (worker->current_pwq->wq->flags & WQ_MEM_RECLAIM),
"workqueue: WQ_MEM_RECLAIM %s:%pf is flushing !WQ_MEM_RECLAIM %s:%pf",
worker->current_pwq->wq->name, worker->current_func,
target_wq->name, target_func);
}
struct wq_barrier {
struct work_struct work;
struct completion done;
@ -2525,6 +2570,8 @@ void flush_workqueue(struct workqueue_struct *wq)
list_add_tail(&this_flusher.list, &wq->flusher_overflow);
}
check_flush_dependency(wq, NULL);
mutex_unlock(&wq->mutex);
wait_for_completion(&this_flusher.done);
@ -2697,6 +2744,8 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr)
pwq = worker->current_pwq;
}
check_flush_dependency(pwq->wq, work);
insert_wq_barrier(pwq, barr, work, worker);
spin_unlock_irq(&pool->lock);
@ -3069,6 +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);
@ -3601,7 +3651,6 @@ static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
const struct workqueue_attrs *attrs)
{
struct apply_wqattrs_ctx *ctx;
int ret = -ENOMEM;
/* only unbound workqueues can change attributes */
if (WARN_ON(!(wq->flags & WQ_UNBOUND)))
@ -3612,16 +3661,14 @@ static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
return -EINVAL;
ctx = apply_wqattrs_prepare(wq, attrs);
if (!ctx)
return -ENOMEM;
/* the ctx has been prepared successfully, let's commit it */
if (ctx) {
apply_wqattrs_commit(ctx);
ret = 0;
}
apply_wqattrs_commit(ctx);
apply_wqattrs_cleanup(ctx);
return ret;
return 0;
}
/**
@ -4308,7 +4355,9 @@ 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));
@ -5167,6 +5216,154 @@ 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;
@ -5290,6 +5487,9 @@ 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);

11
lib/Kconfig.debug
View file

@ -812,6 +812,17 @@ config BOOTPARAM_HUNG_TASK_PANIC_VALUE
default 0 if !BOOTPARAM_HUNG_TASK_PANIC
default 1 if BOOTPARAM_HUNG_TASK_PANIC
config WQ_WATCHDOG
bool "Detect Workqueue Stalls"
depends on DEBUG_KERNEL
help
Say Y here to enable stall detection on workqueues. If a
worker pool doesn't make forward progress on a pending work
item for over a given amount of time, 30s by default, a
warning message is printed along with dump of workqueue
state. This can be configured through kernel parameter
"workqueue.watchdog_thresh" and its sysfs counterpart.
endmenu # "Debug lockups and hangs"
config PANIC_ON_OOPS