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Subject[PATCH] 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.

Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Christoph Hellwig <hch@infradead.org>
---
Christoph, you probably were seeing the rescuer_task->comm in ps
output. wq->name currently is currently only used for error
reporting.

I don't really mind this patch going through a different tree as I
don't have any other wq changes scheduled at this point, so please
feel free to route this through xfs or -mm.

Thank you.

include/linux/workqueue.h | 48 ++++++++++++++++++++++++++++++----------------
kernel/workqueue.c | 32 +++++++++++++++++++++---------
2 files changed, 54 insertions(+), 26 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 0d556de..c87e86b 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -297,32 +297,51 @@ 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, ...)
+ __attribute__((format (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 +350,8 @@ __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 42fa9ad..bec7b5b 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;


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