Merge branch 'for-4.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq
Pull workqueue fixes from Tejun Heo:
"Workqueue fixes for v4.5-rc3.
- Remove a spurious triggering of flush dependency warning.
- Officially break local execution guarantee of unbound work items
and add a debug feature to flush out usages which depend on it.
- Work around CPU -> NODE mapping becoming invalid on CPU offline.
The branch is young but pushing out early as stable kernels are being
affected"
* 'for-4.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
workqueue: handle NUMA_NO_NODE for unbound pool_workqueue lookup
workqueue: implement "workqueue.debug_force_rr_cpu" debug feature
workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs
Revert "workqueue: make sure delayed work run in local cpu"
workqueue: skip flush dependency checks for legacy workqueues
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 551ecf0..9a53c92 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -4235,6 +4235,17 @@
The default value of this parameter is determined by
the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
+ workqueue.debug_force_rr_cpu
+ Workqueue used to implicitly guarantee that work
+ items queued without explicit CPU specified are put
+ on the local CPU. This guarantee is no longer true
+ and while local CPU is still preferred work items
+ may be put on foreign CPUs. This debug option
+ forces round-robin CPU selection to flush out
+ usages which depend on the now broken guarantee.
+ When enabled, memory and cache locality will be
+ impacted.
+
x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 0e32bc7..ca73c50 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -311,6 +311,7 @@
__WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */
__WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */
+ __WQ_LEGACY = 1 << 18, /* internal: create*_workqueue() */
WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */
@@ -411,12 +412,12 @@
alloc_workqueue(fmt, WQ_UNBOUND | __WQ_ORDERED | (flags), 1, ##args)
#define create_workqueue(name) \
- alloc_workqueue("%s", WQ_MEM_RECLAIM, 1, (name))
+ alloc_workqueue("%s", __WQ_LEGACY | WQ_MEM_RECLAIM, 1, (name))
#define create_freezable_workqueue(name) \
- alloc_workqueue("%s", WQ_FREEZABLE | WQ_UNBOUND | WQ_MEM_RECLAIM, \
- 1, (name))
+ alloc_workqueue("%s", __WQ_LEGACY | WQ_FREEZABLE | WQ_UNBOUND | \
+ WQ_MEM_RECLAIM, 1, (name))
#define create_singlethread_workqueue(name) \
- alloc_ordered_workqueue("%s", WQ_MEM_RECLAIM, name)
+ alloc_ordered_workqueue("%s", __WQ_LEGACY | WQ_MEM_RECLAIM, name)
extern void destroy_workqueue(struct workqueue_struct *wq);
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 61a0264..7ff5dc7d 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -301,7 +301,23 @@
static LIST_HEAD(workqueues); /* PR: list of all workqueues */
static bool workqueue_freezing; /* PL: have wqs started freezing? */
-static cpumask_var_t wq_unbound_cpumask; /* PL: low level cpumask for all unbound wqs */
+/* PL: allowable cpus for unbound wqs and work items */
+static cpumask_var_t wq_unbound_cpumask;
+
+/* CPU where unbound work was last round robin scheduled from this CPU */
+static DEFINE_PER_CPU(int, wq_rr_cpu_last);
+
+/*
+ * Local execution of unbound work items is no longer guaranteed. The
+ * following always forces round-robin CPU selection on unbound work items
+ * to uncover usages which depend on it.
+ */
+#ifdef CONFIG_DEBUG_WQ_FORCE_RR_CPU
+static bool wq_debug_force_rr_cpu = true;
+#else
+static bool wq_debug_force_rr_cpu = false;
+#endif
+module_param_named(debug_force_rr_cpu, wq_debug_force_rr_cpu, bool, 0644);
/* the per-cpu worker pools */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
@@ -570,6 +586,16 @@
int node)
{
assert_rcu_or_wq_mutex_or_pool_mutex(wq);
+
+ /*
+ * XXX: @node can be NUMA_NO_NODE if CPU goes offline while a
+ * delayed item is pending. The plan is to keep CPU -> NODE
+ * mapping valid and stable across CPU on/offlines. Once that
+ * happens, this workaround can be removed.
+ */
+ if (unlikely(node == NUMA_NO_NODE))
+ return wq->dfl_pwq;
+
return rcu_dereference_raw(wq->numa_pwq_tbl[node]);
}
@@ -1298,6 +1324,39 @@
return worker && worker->current_pwq->wq == wq;
}
+/*
+ * When queueing an unbound work item to a wq, prefer local CPU if allowed
+ * by wq_unbound_cpumask. Otherwise, round robin among the allowed ones to
+ * avoid perturbing sensitive tasks.
+ */
+static int wq_select_unbound_cpu(int cpu)
+{
+ static bool printed_dbg_warning;
+ int new_cpu;
+
+ if (likely(!wq_debug_force_rr_cpu)) {
+ if (cpumask_test_cpu(cpu, wq_unbound_cpumask))
+ return cpu;
+ } else if (!printed_dbg_warning) {
+ pr_warn("workqueue: round-robin CPU selection forced, expect performance impact\n");
+ printed_dbg_warning = true;
+ }
+
+ if (cpumask_empty(wq_unbound_cpumask))
+ return cpu;
+
+ new_cpu = __this_cpu_read(wq_rr_cpu_last);
+ new_cpu = cpumask_next_and(new_cpu, wq_unbound_cpumask, cpu_online_mask);
+ if (unlikely(new_cpu >= nr_cpu_ids)) {
+ new_cpu = cpumask_first_and(wq_unbound_cpumask, cpu_online_mask);
+ if (unlikely(new_cpu >= nr_cpu_ids))
+ return cpu;
+ }
+ __this_cpu_write(wq_rr_cpu_last, new_cpu);
+
+ return new_cpu;
+}
+
static void __queue_work(int cpu, struct workqueue_struct *wq,
struct work_struct *work)
{
@@ -1323,7 +1382,7 @@
return;
retry:
if (req_cpu == WORK_CPU_UNBOUND)
- cpu = raw_smp_processor_id();
+ cpu = wq_select_unbound_cpu(raw_smp_processor_id());
/* pwq which will be used unless @work is executing elsewhere */
if (!(wq->flags & WQ_UNBOUND))
@@ -1464,13 +1523,13 @@
timer_stats_timer_set_start_info(&dwork->timer);
dwork->wq = wq;
- /* timer isn't guaranteed to run in this cpu, record earlier */
- if (cpu == WORK_CPU_UNBOUND)
- cpu = raw_smp_processor_id();
dwork->cpu = cpu;
timer->expires = jiffies + delay;
- add_timer_on(timer, cpu);
+ if (unlikely(cpu != WORK_CPU_UNBOUND))
+ add_timer_on(timer, cpu);
+ else
+ add_timer(timer);
}
/**
@@ -2355,7 +2414,8 @@
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),
+ WARN_ONCE(worker && ((worker->current_pwq->wq->flags &
+ (WQ_MEM_RECLAIM | __WQ_LEGACY)) == 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);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index ecb9e75..8bfd1ac 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1400,6 +1400,21 @@
endmenu # "RCU Debugging"
+config DEBUG_WQ_FORCE_RR_CPU
+ bool "Force round-robin CPU selection for unbound work items"
+ depends on DEBUG_KERNEL
+ default n
+ help
+ Workqueue used to implicitly guarantee that work items queued
+ without explicit CPU specified are put on the local CPU. This
+ guarantee is no longer true and while local CPU is still
+ preferred work items may be put on foreign CPUs. Kernel
+ parameter "workqueue.debug_force_rr_cpu" is added to force
+ round-robin CPU selection to flush out usages which depend on the
+ now broken guarantee. This config option enables the debug
+ feature by default. When enabled, memory and cache locality will
+ be impacted.
+
config DEBUG_BLOCK_EXT_DEVT
bool "Force extended block device numbers and spread them"
depends on DEBUG_KERNEL