workqueue: Allow retrieval of current task's work struct

[ Upstream commit 27d4ee03078aba88c5e07dcc4917e8d01d046f38 ]

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: Sasha Levin <alexander.levin@microsoft.com>

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index deee212af8e0939a6d97189569cf8199fb840124..e450bdbc4d84bae01f3cfc0f1e6e9c2f6f59f4e7 100644 (file)
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -449,6 +449,7 @@ 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 376db986db9bc7164c15bc02c9837b86c6ff3b6f..782ba721984b0ea4a1561cdfcc34aa6b945ce550 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4062,6 +4062,22 @@ 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?
  *