drm/radeon: Make sure CS mutex is held across GPU reset.

This was only the case if the GPU reset was triggered from the CS ioctl,
otherwise other processes could happily enter the CS ioctl and wreak havoc
during the GPU reset.

This is a little complicated because the GPU reset can be triggered from the
CS ioctl, in which case we're already holding the mutex, or from other call
paths, in which case we need to lock the mutex. AFAICT the mutex API doesn't
allow recursive locking or finding out the mutex owner, so we need to handle
this with helper functions which allow recursive locking from the same
process.

Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 43 insertions, 1 deletions

diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
index b316b301152f..85ef693850e7 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -1142,6 +1142,48 @@ struct r600_vram_scratch {
         u64                             gpu_addr;
 };
 
+
+/*
+ * Mutex which allows recursive locking from the same process.
+ */
+struct radeon_mutex {
+        struct mutex            mutex;
+        struct task_struct      *owner;
+        int                     level;
+};
+
+static inline void radeon_mutex_init(struct radeon_mutex *mutex)
+{
+        mutex_init(&mutex->mutex);
+        mutex->owner = NULL;
+        mutex->level = 0;
+}
+
+static inline void radeon_mutex_lock(struct radeon_mutex *mutex)
+{
+        if (mutex_trylock(&mutex->mutex)) {
+                /* The mutex was unlocked before, so it's ours now */
+                mutex->owner = current;
+        } else if (mutex->owner != current) {
+                /* Another process locked the mutex, take it */
+                mutex_lock(&mutex->mutex);
+                mutex->owner = current;
+        }
+        /* Otherwise the mutex was already locked by this process */
+
+        mutex->level++;
+}
+
+static inline void radeon_mutex_unlock(struct radeon_mutex *mutex)
+{
+        if (--mutex->level > 0)
+                return;
+
+        mutex->owner = NULL;
+        mutex_unlock(&mutex->mutex);
+}
+
+
 /*
  * Core structure, functions and helpers.
  */
@@ -1197,7 +1239,7 @@ struct radeon_device {
         struct radeon_gem               gem;
         struct radeon_pm                pm;
         uint32_t                        bios_scratch[RADEON_BIOS_NUM_SCRATCH];
-        struct mutex                    cs_mutex;
+        struct radeon_mutex             cs_mutex;
         struct radeon_wb                wb;
         struct radeon_dummy_page        dummy_page;
         bool                            gpu_lockup;