In the fbdev code we want to do trylocks only to avoid deadlocks and
other ugly issues. Thus far we've only grabbed the overall modeset
lock, but that already failed to exclude a pile of potential
concurrent operations. With proper atomic support this will be worse.
So add a trylock mode to the modeset locking code which attempts all
locks only with trylocks, if possible. We need to track this in the
locking functions themselves and can't restrict this to drivers since
driver-private w/w mutexes must be treated the same way.
There's still the issue that other driver private locks aren't handled
here at all, but well can't have everything. With this we will at
least not regress, even once atomic allows lots of concurrent kms
activity.
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
drivers/gpu/drm/drm_fb_helper.c | 10 ++++----
drivers/gpu/drm/drm_modeset_lock.c | 51 +++++++++++++++++++++++++++-----------
include/drm/drm_modeset_lock.h | 6 +++++
3 files changed, 47 insertions(+), 20 deletions(-)
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 3144db9dc0f1..66a438ab4e7f 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -419,11 +419,11 @@ static bool drm_fb_helper_force_kernel_mode(void)
if (dev->switch_power_state == DRM_SWITCH_POWER_OFF)
continue;
- /* NOTE: we use lockless flag below to avoid grabbing other
- * modeset locks. So just trylock the underlying mutex
- * directly:
+ /*
+ * NOTE: Use trylock mode to avoid deadlocks and sleeping in
+ * panic context.
*/
- if (!mutex_trylock(&dev->mode_config.mutex)) {
+ if (!__drm_modeset_lock_all(dev, true)) {
error = true;
continue;
}
@@ -432,7 +432,7 @@ static bool drm_fb_helper_force_kernel_mode(void)
if (ret)
error = true;
- mutex_unlock(&dev->mode_config.mutex);
+ drm_modeset_unlock_all(dev);
}
return error;
}
diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
index 412b396af740..42ba9ca699ad 100644
--- a/drivers/gpu/drm/drm_modeset_lock.c
+++ b/drivers/gpu/drm/drm_modeset_lock.c
@@ -56,27 +56,27 @@
*/
-/**
- * drm_modeset_lock_all - take all modeset locks
- * @dev: drm device
- *
- * This function takes all modeset locks, suitable where a more fine-grained
- * scheme isn't (yet) implemented. Locks must be dropped with
- * drm_modeset_unlock_all.
- */
-void drm_modeset_lock_all(struct drm_device *dev)
+int __drm_modeset_lock_all(struct drm_device *dev,
+ bool trylock)
{
struct drm_mode_config *config = &dev->mode_config;
struct drm_modeset_acquire_ctx *ctx;
int ret;
- ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
- if (WARN_ON(!ctx))
- return;
+ ctx = kzalloc(sizeof(*ctx),
+ trylock ? GFP_ATOMIC : GFP_KERNEL);
+ if (!ctx)
+ return -ENOMEM;
- mutex_lock(&config->mutex);
+ if (trylock) {
+ if (!mutex_trylock(&config->mutex))
+ return -EBUSY;
+ } else {
+ mutex_lock(&config->mutex);
+ }
drm_modeset_acquire_init(ctx, 0);
+ ctx->trylock_only = trylock;
retry:
ret = drm_modeset_lock(&config->connection_mutex, ctx);
@@ -95,13 +95,29 @@ retry:
drm_warn_on_modeset_not_all_locked(dev);
- return;
+ return 0;
fail:
if (ret == -EDEADLK) {
drm_modeset_backoff(ctx);
goto retry;
}
+
+ return ret;
+}
+EXPORT_SYMBOL(__drm_modeset_lock_all);
+
+/**
+ * drm_modeset_lock_all - take all modeset locks
+ * @dev: drm device
+ *
+ * This function takes all modeset locks, suitable where a more fine-grained
+ * scheme isn't (yet) implemented. Locks must be dropped with
+ * drm_modeset_unlock_all.
+ */
+void drm_modeset_lock_all(struct drm_device *dev)
+{
+ WARN_ON(__drm_modeset_lock_all(dev, false) != 0);
}
EXPORT_SYMBOL(drm_modeset_lock_all);
@@ -287,7 +303,12 @@ static inline int modeset_lock(struct drm_modeset_lock *lock,
WARN_ON(ctx->contended);
- if (interruptible && slow) {
+ if (ctx->trylock_only) {
+ if (!ww_mutex_trylock(&lock->mutex))
+ return -EBUSY;
+ else
+ return 0;
+ } else if (interruptible && slow) {
ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
} else if (interruptible) {
ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
diff --git a/include/drm/drm_modeset_lock.h b/include/drm/drm_modeset_lock.h
index d38e1508f11a..a3f736d24382 100644
--- a/include/drm/drm_modeset_lock.h
+++ b/include/drm/drm_modeset_lock.h
@@ -53,6 +53,11 @@ struct drm_modeset_acquire_ctx {
* list of held locks (drm_modeset_lock)
*/
struct list_head locked;
+
+ /**
+ * Trylock mode, use only for panic handlers!
+ */
+ bool trylock_only;
};
/**
@@ -123,6 +128,7 @@ struct drm_device;
struct drm_crtc;
void drm_modeset_lock_all(struct drm_device *dev);
+int __drm_modeset_lock_all(struct drm_device *dev, bool trylock);
void drm_modeset_unlock_all(struct drm_device *dev);
void drm_modeset_lock_crtc(struct drm_crtc *crtc);
void drm_modeset_unlock_crtc(struct drm_crtc *crtc);
--
2.0.1
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