workqueue: introduce workqueue_attrs

Introduce struct workqueue_attrs which carries worker attributes -
currently the nice level and allowed cpumask along with helper
routines alloc_workqueue_attrs() and free_workqueue_attrs().

Each worker_pool now carries ->attrs describing the attributes of its
workers.  All functions dealing with cpumask and nice level of workers
are updated to follow worker_pool->attrs instead of determining them
from other characteristics of the worker_pool, and init_workqueues()
is updated to set worker_pool->attrs appropriately for all standard
pools.

Note that create_worker() is updated to always perform set_user_nice()
and use set_cpus_allowed_ptr() combined with manual assertion of
PF_THREAD_BOUND instead of kthread_bind().  This simplifies handling
random attributes without affecting the outcome.

This patch doesn't introduce any behavior changes.

v2: Missing cpumask_var_t definition caused build failure on some
    archs.  linux/cpumask.h included.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>

2 files changed, 94 insertions, 22 deletions

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 899be6636d20..00c1b9ba8252 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -11,6 +11,7 @@
 #include <linux/lockdep.h>
 #include <linux/threads.h>
 #include <linux/atomic.h>
+#include <linux/cpumask.h>
 
 struct workqueue_struct;
 
@@ -115,6 +116,15 @@ struct delayed_work {
         int cpu;
 };
 
+/*
+ * A struct for workqueue attributes.  This can be used to change
+ * attributes of an unbound workqueue.
+ */
+struct workqueue_attrs {
+        int                     nice;           /* nice level */
+        cpumask_var_t           cpumask;        /* allowed CPUs */
+};
+
 static inline struct delayed_work *to_delayed_work(struct work_struct *work)
 {
         return container_of(work, struct delayed_work, work);
@@ -399,6 +409,9 @@ __alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,
 
 extern void destroy_workqueue(struct workqueue_struct *wq);
 
+struct workqueue_attrs *alloc_workqueue_attrs(gfp_t gfp_mask);
+void free_workqueue_attrs(struct workqueue_attrs *attrs);
+
 extern bool queue_work_on(int cpu, struct workqueue_struct *wq,
                         struct work_struct *work);
 extern bool queue_work(struct workqueue_struct *wq, struct work_struct *work);
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 094f16668e1b..b0d3cbb83f63 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -148,6 +148,8 @@ struct worker_pool {
         struct mutex            assoc_mutex;    /* protect POOL_DISASSOCIATED */
         struct ida              worker_ida;     /* L: for worker IDs */
 
+        struct workqueue_attrs  *attrs;         /* I: worker attributes */
+
         /*
          * The current concurrency level.  As it's likely to be accessed
          * from other CPUs during try_to_wake_up(), put it in a separate
@@ -1566,14 +1568,13 @@ __acquires(&pool->lock)
                  * against POOL_DISASSOCIATED.
                  */
                 if (!(pool->flags & POOL_DISASSOCIATED))
-                        set_cpus_allowed_ptr(current, get_cpu_mask(pool->cpu));
+                        set_cpus_allowed_ptr(current, pool->attrs->cpumask);
 
                 spin_lock_irq(&pool->lock);
                 if (pool->flags & POOL_DISASSOCIATED)
                         return false;
                 if (task_cpu(current) == pool->cpu &&
-                    cpumask_equal(&current->cpus_allowed,
-                                  get_cpu_mask(pool->cpu)))
+                    cpumask_equal(&current->cpus_allowed, pool->attrs->cpumask))
                         return true;
                 spin_unlock_irq(&pool->lock);
 
@@ -1679,7 +1680,7 @@ static void rebind_workers(struct worker_pool *pool)
                  * wq doesn't really matter but let's keep @worker->pool
                  * and @pwq->pool consistent for sanity.
                  */
-                if (std_worker_pool_pri(worker->pool))
+                if (worker->pool->attrs->nice < 0)
                         wq = system_highpri_wq;
                 else
                         wq = system_wq;
@@ -1721,7 +1722,7 @@ static struct worker *alloc_worker(void)
  */
 static struct worker *create_worker(struct worker_pool *pool)
 {
-        const char *pri = std_worker_pool_pri(pool) ? "H" : "";
+        const char *pri = pool->attrs->nice < 0  ? "H" : "";
         struct worker *worker = NULL;
         int id = -1;
 
@@ -1751,24 +1752,23 @@ static struct worker *create_worker(struct worker_pool *pool)
         if (IS_ERR(worker->task))
                 goto fail;
 
-        if (std_worker_pool_pri(pool))
-                set_user_nice(worker->task, HIGHPRI_NICE_LEVEL);
+        set_user_nice(worker->task, pool->attrs->nice);
+        set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
 
         /*
-         * Determine CPU binding of the new worker depending on
-         * %POOL_DISASSOCIATED.  The caller is responsible for ensuring the
-         * flag remains stable across this function.  See the comments
-         * above the flag definition for details.
-         *
-         * As an unbound worker may later become a regular one if CPU comes
-         * online, make sure every worker has %PF_THREAD_BOUND set.
+         * %PF_THREAD_BOUND is used to prevent userland from meddling with
+         * cpumask of workqueue workers.  This is an abuse.  We need
+         * %PF_NO_SETAFFINITY.
          */
-        if (!(pool->flags & POOL_DISASSOCIATED)) {
-                kthread_bind(worker->task, pool->cpu);
-        } else {
-                worker->task->flags |= PF_THREAD_BOUND;
+        worker->task->flags |= PF_THREAD_BOUND;
+
+        /*
+         * The caller is responsible for ensuring %POOL_DISASSOCIATED
+         * remains stable across this function.  See the comments above the
+         * flag definition for details.
+         */
+        if (pool->flags & POOL_DISASSOCIATED)
                 worker->flags |= WORKER_UNBOUND;
-        }
 
         return worker;
 fail:
@@ -3123,7 +3123,52 @@ int keventd_up(void)
         return system_wq != NULL;
 }
 
-static void init_worker_pool(struct worker_pool *pool)
+/**
+ * free_workqueue_attrs - free a workqueue_attrs
+ * @attrs: workqueue_attrs to free
+ *
+ * Undo alloc_workqueue_attrs().
+ */
+void free_workqueue_attrs(struct workqueue_attrs *attrs)
+{
+        if (attrs) {
+                free_cpumask_var(attrs->cpumask);
+                kfree(attrs);
+        }
+}
+
+/**
+ * alloc_workqueue_attrs - allocate a workqueue_attrs
+ * @gfp_mask: allocation mask to use
+ *
+ * Allocate a new workqueue_attrs, initialize with default settings and
+ * return it.  Returns NULL on failure.
+ */
+struct workqueue_attrs *alloc_workqueue_attrs(gfp_t gfp_mask)
+{
+        struct workqueue_attrs *attrs;
+
+        attrs = kzalloc(sizeof(*attrs), gfp_mask);
+        if (!attrs)
+                goto fail;
+        if (!alloc_cpumask_var(&attrs->cpumask, gfp_mask))
+                goto fail;
+
+        cpumask_setall(attrs->cpumask);
+        return attrs;
+fail:
+        free_workqueue_attrs(attrs);
+        return NULL;
+}
+
+/**
+ * init_worker_pool - initialize a newly zalloc'd worker_pool
+ * @pool: worker_pool to initialize
+ *
+ * Initiailize a newly zalloc'd @pool.  It also allocates @pool->attrs.
+ * Returns 0 on success, -errno on failure.
+ */
+static int init_worker_pool(struct worker_pool *pool)
 {
         spin_lock_init(&pool->lock);
         pool->flags |= POOL_DISASSOCIATED;
@@ -3141,6 +3186,11 @@ static void init_worker_pool(struct worker_pool *pool)
         mutex_init(&pool->manager_arb);
         mutex_init(&pool->assoc_mutex);
         ida_init(&pool->worker_ida);
+
+        pool->attrs = alloc_workqueue_attrs(GFP_KERNEL);
+        if (!pool->attrs)
+                return -ENOMEM;
+        return 0;
 }
 
 static int alloc_and_link_pwqs(struct workqueue_struct *wq)
@@ -3792,7 +3842,8 @@ out_unlock:
 
 static int __init init_workqueues(void)
 {
-        int cpu;
+        int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL };
+        int i, cpu;
 
         /* make sure we have enough bits for OFFQ pool ID */
         BUILD_BUG_ON((1LU << (BITS_PER_LONG - WORK_OFFQ_POOL_SHIFT)) <
@@ -3809,10 +3860,18 @@ static int __init init_workqueues(void)
         for_each_wq_cpu(cpu) {
                 struct worker_pool *pool;
 
+                i = 0;
                 for_each_std_worker_pool(pool, cpu) {
-                        init_worker_pool(pool);
+                        BUG_ON(init_worker_pool(pool));
                         pool->cpu = cpu;
 
+                        if (cpu != WORK_CPU_UNBOUND)
+                                cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu));
+                        else
+                                cpumask_setall(pool->attrs->cpumask);
+
+                        pool->attrs->nice = std_nice[i++];
+
                         /* alloc pool ID */
                         BUG_ON(worker_pool_assign_id(pool));
                 }