drm/msm: show task cmdline in gpu recovery messages

Now that freedreno gallium driver defaults to using submit_queue task
(render reordering), just showing task->comm is not so useful (ie. it is
always "flush_queue:0"), so also dump the cmdline.  This should also be
more useful for piglit/shader_runner.
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/msm_gpu.c

@@ -20,6 +20,8 @@
 #include "msm_mmu.h"
 #include "msm_fence.h"
 
+#include <linux/string_helpers.h>
+
 
 /*
  * Power Management:
@@ -235,6 +237,20 @@ static void update_fences(struct msm_gpu *gpu, struct msm_ringbuffer *ring,
 	}
 }
 
+static struct msm_gem_submit *
+find_submit(struct msm_ringbuffer *ring, uint32_t fence)
+{
+	struct msm_gem_submit *submit;
+
+	WARN_ON(!mutex_is_locked(&ring->gpu->dev->struct_mutex));
+
+	list_for_each_entry(submit, &ring->submits, node)
+		if (submit->seqno == fence)
+			return submit;
+
+	return NULL;
+}
+
 static void retire_submits(struct msm_gpu *gpu);
 
 static void recover_worker(struct work_struct *work)
@@ -268,19 +284,34 @@ static void recover_worker(struct work_struct *work)
 	dev_err(dev->dev, "%s: hangcheck recover!\n", gpu->name);
 	fence = cur_ring->memptrs->fence + 1;
 
-	list_for_each_entry(submit, &cur_ring->submits, node) {
-		if (submit->seqno == fence) {
-			struct task_struct *task;
-
-			rcu_read_lock();
-			task = pid_task(submit->pid, PIDTYPE_PID);
-			if (task) {
-				dev_err(dev->dev, "%s: offending task: %s\n",
-						gpu->name, task->comm);
-			}
-			rcu_read_unlock();
-			break;
+	submit = find_submit(cur_ring, fence);
+	if (submit) {
+		struct task_struct *task;
+
+		rcu_read_lock();
+		task = pid_task(submit->pid, PIDTYPE_PID);
+		if (task) {
+			char *cmd;
+
+			/*
+			 * So slightly annoying, in other paths like
+			 * mmap'ing gem buffers, mmap_sem is acquired
+			 * before struct_mutex, which means we can't
+			 * hold struct_mutex across the call to
+			 * get_cmdline().  But submits are retired
+			 * from the same in-order workqueue, so we can
+			 * safely drop the lock here without worrying
+			 * about the submit going away.
+			 */
+			mutex_unlock(&dev->struct_mutex);
+			cmd = kstrdup_quotable_cmdline(task, GFP_KERNEL);
+			mutex_lock(&dev->struct_mutex);
+
+			dev_err(dev->dev, "%s: offending task: %s (%s)\n",
+				gpu->name, task->comm, cmd);
 		}
+		rcu_read_unlock();
+
 	}
 
 	if (msm_gpu_active(gpu)) {