workqueue: make alloc_workqueue() take printf fmt and args for name

alloc_workqueue() currently expects the passed in @name pointer to remain
accessible.  This is inconvenient and a bit silly given that the whole wq
is being dynamically allocated.  This patch updates alloc_workqueue() and
friends to take printf format string instead of opaque string and matching
varargs at the end.  The name is allocated together with the wq and
formatted.

alloc_ordered_workqueue() is converted to a macro to unify varargs
handling with alloc_workqueue(), and, while at it, add comment to
alloc_workqueue().

None of the current in-kernel users pass in string with '%' as constant
name and this change shouldn't cause any problem.

[akpm@linux-foundation.org: use __printf]
Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 53 insertions, 26 deletions

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 0d556deb497b..eb8b9f15f2e0 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -297,32 +297,50 @@ extern struct workqueue_struct *system_unbound_wq;
 extern struct workqueue_struct *system_freezable_wq;
 
 extern struct workqueue_struct *
-__alloc_workqueue_key(const char *name, unsigned int flags, int max_active,
-                      struct lock_class_key *key, const char *lock_name);
+__alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,
+        struct lock_class_key *key, const char *lock_name, ...) __printf(1, 6);
 
+/**
+ * alloc_workqueue - allocate a workqueue
+ * @fmt: printf format for the name of the workqueue
+ * @flags: WQ_* flags
+ * @max_active: max in-flight work items, 0 for default
+ * @args: args for @fmt
+ *
+ * Allocate a workqueue with the specified parameters.  For detailed
+ * information on WQ_* flags, please refer to Documentation/workqueue.txt.
+ *
+ * The __lock_name macro dance is to guarantee that single lock_class_key
+ * doesn't end up with different namesm, which isn't allowed by lockdep.
+ *
+ * RETURNS:
+ * Pointer to the allocated workqueue on success, %NULL on failure.
+ */
 #ifdef CONFIG_LOCKDEP
-#define alloc_workqueue(name, flags, max_active)                \
+#define alloc_workqueue(fmt, flags, max_active, args...)        \
 ({                                                              \
         static struct lock_class_key __key;                     \
         const char *__lock_name;                                \
                                                                 \
-        if (__builtin_constant_p(name))                         \
-                __lock_name = (name);                           \
+        if (__builtin_constant_p(fmt))                          \
+                __lock_name = (fmt);                            \
         else                                                    \
-                __lock_name = #name;                            \
+                __lock_name = #fmt;                             \
                                                                 \
-        __alloc_workqueue_key((name), (flags), (max_active),    \
-                              &__key, __lock_name);             \
+        __alloc_workqueue_key((fmt), (flags), (max_active),     \
+                              &__key, __lock_name, ##args);     \
 })
 #else
-#define alloc_workqueue(name, flags, max_active)                \
-        __alloc_workqueue_key((name), (flags), (max_active), NULL, NULL)
+#define alloc_workqueue(fmt, flags, max_active, args...)        \
+        __alloc_workqueue_key((fmt), (flags), (max_active),     \
+                              NULL, NULL, ##args)
 #endif
 
 /**
  * alloc_ordered_workqueue - allocate an ordered workqueue
- * @name: name of the workqueue
+ * @fmt: printf format for the name of the workqueue
  * @flags: WQ_* flags (only WQ_FREEZABLE and WQ_MEM_RECLAIM are meaningful)
+ * @args: args for @fmt
  *
  * Allocate an ordered workqueue.  An ordered workqueue executes at
  * most one work item at any given time in the queued order.  They are
@@ -331,11 +349,8 @@ __alloc_workqueue_key(const char *name, unsigned int flags, int max_active,
  * RETURNS:
  * Pointer to the allocated workqueue on success, %NULL on failure.
  */
-static inline struct workqueue_struct *
-alloc_ordered_workqueue(const char *name, unsigned int flags)
-{
-        return alloc_workqueue(name, WQ_UNBOUND | flags, 1);
-}
+#define alloc_ordered_workqueue(fmt, flags, args...)            \
+        alloc_workqueue(fmt, WQ_UNBOUND | (flags), 1, ##args)
 
 #define create_workqueue(name)                                  \
         alloc_workqueue((name), WQ_MEM_RECLAIM, 1)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 42fa9ad0a810..bec7b5b53e03 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -242,10 +242,10 @@ struct workqueue_struct {
 
         int                     nr_drainers;    /* W: drain in progress */
         int                     saved_max_active; /* W: saved cwq max_active */
-        const char              *name;          /* I: workqueue name */
 #ifdef CONFIG_LOCKDEP
         struct lockdep_map      lockdep_map;
 #endif
+        char                    name[];         /* I: workqueue name */
 };
 
 struct workqueue_struct *system_wq __read_mostly;
@@ -2954,14 +2954,29 @@ static int wq_clamp_max_active(int max_active, unsigned int flags,
         return clamp_val(max_active, 1, lim);
 }
 
-struct workqueue_struct *__alloc_workqueue_key(const char *name,
+struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
                                                unsigned int flags,
                                                int max_active,
                                                struct lock_class_key *key,
-                                               const char *lock_name)
+                                               const char *lock_name, ...)
 {
+        va_list args, args1;
         struct workqueue_struct *wq;
         unsigned int cpu;
+        size_t namelen;
+
+        /* determine namelen, allocate wq and format name */
+        va_start(args, lock_name);
+        va_copy(args1, args);
+        namelen = vsnprintf(NULL, 0, fmt, args) + 1;
+
+        wq = kzalloc(sizeof(*wq) + namelen, GFP_KERNEL);
+        if (!wq)
+                goto err;
+
+        vsnprintf(wq->name, namelen, fmt, args1);
+        va_end(args);
+        va_end(args1);
 
         /*
          * Workqueues which may be used during memory reclaim should
@@ -2978,12 +2993,9 @@ struct workqueue_struct *__alloc_workqueue_key(const char *name,
                 flags |= WQ_HIGHPRI;
 
         max_active = max_active ?: WQ_DFL_ACTIVE;
-        max_active = wq_clamp_max_active(max_active, flags, name);
-
-        wq = kzalloc(sizeof(*wq), GFP_KERNEL);
-        if (!wq)
-                goto err;
+        max_active = wq_clamp_max_active(max_active, flags, wq->name);
 
+        /* init wq */
         wq->flags = flags;
         wq->saved_max_active = max_active;
         mutex_init(&wq->flush_mutex);
@@ -2991,7 +3003,6 @@ struct workqueue_struct *__alloc_workqueue_key(const char *name,
         INIT_LIST_HEAD(&wq->flusher_queue);
         INIT_LIST_HEAD(&wq->flusher_overflow);
 
-        wq->name = name;
         lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
         INIT_LIST_HEAD(&wq->list);
 
@@ -3020,7 +3031,8 @@ struct workqueue_struct *__alloc_workqueue_key(const char *name,
                 if (!rescuer)
                         goto err;
 
-                rescuer->task = kthread_create(rescuer_thread, wq, "%s", name);
+                rescuer->task = kthread_create(rescuer_thread, wq, "%s",
+                                               wq->name);
                 if (IS_ERR(rescuer->task))
                         goto err;