workqueue: Allow retrieval of current task's work struct

commit 27d4ee03078aba88c5e07dcc4917e8d01d046f38 upstream.

Introduce a helper to retrieve the current task's work struct if it is
a workqueue worker.

This allows us to fix a long-standing deadlock in several DRM drivers
wherein the ->runtime_suspend callback waits for a specific worker to
finish and that worker in turn calls a function which waits for runtime
suspend to finish.  That function is invoked from multiple call sites
and waiting for runtime suspend to finish is the correct thing to do
except if it's executing in the context of the worker.

Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://patchwork.freedesktop.org/patch/msgid/2d8f603074131eb87e588d2b803a71765bd3a2fd.1518338788.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 217abe56e711b180b0cb14d6899df78d0a101b29..f63ce973b27b097e4ac118e224893a5f2d8a9fe0 100644 (file)
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -451,6 +451,7 @@ extern bool cancel_delayed_work_sync(struct delayed_work *dwork);
 
 extern void workqueue_set_max_active(struct workqueue_struct *wq,
                                     int max_active);
+extern struct work_struct *current_work(void);
 extern bool current_is_workqueue_rescuer(void);
 extern bool workqueue_congested(int cpu, struct workqueue_struct *wq);
 extern unsigned int work_busy(struct work_struct *work);

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 85555eb4d3cb5a2fcafa55d234537aa1515d8cf9..8df77ed6aa99c23bdf485585201c926408632a33 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4047,6 +4047,22 @@ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
 }
 EXPORT_SYMBOL_GPL(workqueue_set_max_active);
 
+/**
+ * current_work - retrieve %current task's work struct
+ *
+ * Determine if %current task is a workqueue worker and what it's working on.
+ * Useful to find out the context that the %current task is running in.
+ *
+ * Return: work struct if %current task is a workqueue worker, %NULL otherwise.
+ */
+struct work_struct *current_work(void)
+{
+       struct worker *worker = current_wq_worker();
+
+       return worker ? worker->current_work : NULL;
+}
+EXPORT_SYMBOL(current_work);
+
 /**
  * current_is_workqueue_rescuer - is %current workqueue rescuer?
  *