[PATCH v2 0/6] drm/atomic: Interruptible locks for everyone!

[PATCH v2 0/6] drm/atomic: Interruptible locks for everyone!

[Maarten Lankhorst]

drm_atomic_commit could previous have always failed when waits failed,
but locking was always done uninterruptibly. Add infrastructure to make
it possible for callers to choose interruptible locking, and convert the
5 most common ioctl's to use it.

All other atomic helpers can be converted when additional tests are added
to kms_atomic_interruptible.

Changes since last version:
- Small fixes to the preparation patch
- Convert setcrtc as well.

Maarten Lankhorst (6):
  drm/atomic: Prepare drm_modeset_lock infrastructure for interruptible
    waiting, v2.
  drm/atomic: Convert atomic ioctl locking to interruptible.
  drm/legacy: Convert cursor ioctl locking to interruptible.
  drm/legacy: Convert setplane ioctl locking to interruptible.
  drm/atomic: Convert pageflip ioctl locking to interruptible.
  drm/crtc: Convert setcrtc ioctl locking to interruptible.

 drivers/gpu/drm/drm_atomic.c       |  7 +--
 drivers/gpu/drm/drm_crtc.c         |  7 +--
 drivers/gpu/drm/drm_debugfs_crc.c  |  2 +-
 drivers/gpu/drm/drm_modeset_lock.c | 96 +++++++++++++++++++-------------------
 drivers/gpu/drm/drm_plane.c        | 21 +++++----
 include/drm/drm_modeset_lock.h     | 12 +++--
 6 files changed, 77 insertions(+), 68 deletions(-)

-- 
2.14.1

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[PATCH v2 1/6] drm/atomic: Prepare drm_modeset_lock infrastructure for interruptible waiting, v2.

[Maarten Lankhorst]

When we want to make drm_atomic_commit interruptible, there are a lot of
places that call the lock function, which we don't have control over.

Rather than trying to convert every single one, it's easier to toggle
interruptible waiting per acquire_ctx. If drm_modeset_acquire_init is
called with DRM_MODESET_ACQUIRE_INTERRUPTIBLE, then we will perform
interruptible waits in drm_modeset_lock and drm_modeset_backoff.

Changes since v1:
- Fix locking example in drm_modeset_lock.c to be compatible
  with interruptible waiting (xexaxo) and make it default.
  Uninterruptible waiting shouldn't happen except in corner cases,
  but the example will still apply if the flag is removed.
- Add drm_modeset_lock_single_interruptible() to documentation.
- Fix dead link to removed drm_modeset_lock_interruptible() in
  drm_modeset_lock().

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> #v1
Cc: Emil Velikov <emil.l.velikov@gmail.com>
---
 drivers/gpu/drm/drm_debugfs_crc.c  |  2 +-
 drivers/gpu/drm/drm_modeset_lock.c | 96 +++++++++++++++++++-------------------
 include/drm/drm_modeset_lock.h     | 12 +++--
 3 files changed, 57 insertions(+), 53 deletions(-)

diff --git a/drivers/gpu/drm/drm_debugfs_crc.c b/drivers/gpu/drm/drm_debugfs_crc.c
index f9e26dda56d6..9dd879589a2c 100644
--- a/drivers/gpu/drm/drm_debugfs_crc.c
+++ b/drivers/gpu/drm/drm_debugfs_crc.c
@@ -155,7 +155,7 @@ static int crtc_crc_open(struct inode *inode, struct file *filep)
 	int ret = 0;
 
 	if (drm_drv_uses_atomic_modeset(crtc->dev)) {
-		ret = drm_modeset_lock_interruptible(&crtc->mutex, NULL);
+		ret = drm_modeset_lock_single_interruptible(&crtc->mutex);
 		if (ret)
 			return ret;
 
diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
index af4e906c630d..e123497da0ca 100644
--- a/drivers/gpu/drm/drm_modeset_lock.c
+++ b/drivers/gpu/drm/drm_modeset_lock.c
@@ -39,23 +39,28 @@
  *
  * The basic usage pattern is to::
  *
- *     drm_modeset_acquire_init(&ctx)
+ *     drm_modeset_acquire_init(ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
  *     retry:
  *     foreach (lock in random_ordered_set_of_locks) {
- *         ret = drm_modeset_lock(lock, &ctx)
+ *         ret = drm_modeset_lock(lock, ctx)
  *         if (ret == -EDEADLK) {
- *             drm_modeset_backoff(&ctx);
- *             goto retry;
+ *             ret = drm_modeset_backoff(ctx);
+ *             if (!ret)
+ *                 goto retry;
  *         }
+ *         if (ret)
+ *             goto out;
  *     }
  *     ... do stuff ...
- *     drm_modeset_drop_locks(&ctx);
- *     drm_modeset_acquire_fini(&ctx);
+ *     out:
+ *     drm_modeset_drop_locks(ctx);
+ *     drm_modeset_acquire_fini(ctx);
  *
  * If all that is needed is a single modeset lock, then the &struct
  * drm_modeset_acquire_ctx is not needed and the locking can be simplified
- * by passing a NULL instead of ctx in the drm_modeset_lock()
- * call and, when done, by calling drm_modeset_unlock().
+ * by passing a NULL instead of ctx in the drm_modeset_lock() call or
+ * calling  drm_modeset_lock_single_interruptible(). To unlock afterwards
+ * call drm_modeset_unlock().
  *
  * On top of these per-object locks using &ww_mutex there's also an overall
  * &drm_mode_config.mutex, for protecting everything else. Mostly this means
@@ -178,7 +183,11 @@ EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
 /**
  * drm_modeset_acquire_init - initialize acquire context
  * @ctx: the acquire context
- * @flags: for future
+ * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE
+ *
+ * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags,
+ * all calls to drm_modeset_lock() will perform an interruptible
+ * wait.
  */
 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
 		uint32_t flags)
@@ -186,6 +195,9 @@ void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
 	memset(ctx, 0, sizeof(*ctx));
 	ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
 	INIT_LIST_HEAD(&ctx->locked);
+
+	if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
+		ctx->interruptible = true;
 }
 EXPORT_SYMBOL(drm_modeset_acquire_init);
 
@@ -261,8 +273,19 @@ static inline int modeset_lock(struct drm_modeset_lock *lock,
 	return ret;
 }
 
-static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
-		bool interruptible)
+/**
+ * drm_modeset_backoff - deadlock avoidance backoff
+ * @ctx: the acquire context
+ *
+ * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
+ * you must call this function to drop all currently held locks and
+ * block until the contended lock becomes available.
+ *
+ * This function returns 0 on success, or -ERESTARTSYS if this context
+ * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the
+ * wait has been interrupted.
+ */
+int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
 {
 	struct drm_modeset_lock *contended = ctx->contended;
 
@@ -273,35 +296,10 @@ static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
 
 	drm_modeset_drop_locks(ctx);
 
-	return modeset_lock(contended, ctx, interruptible, true);
-}
-
-/**
- * drm_modeset_backoff - deadlock avoidance backoff
- * @ctx: the acquire context
- *
- * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
- * you must call this function to drop all currently held locks and
- * block until the contended lock becomes available.
- */
-void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
-{
-	modeset_backoff(ctx, false);
+	return modeset_lock(contended, ctx, ctx->interruptible, true);
 }
 EXPORT_SYMBOL(drm_modeset_backoff);
 
-/**
- * drm_modeset_backoff_interruptible - deadlock avoidance backoff
- * @ctx: the acquire context
- *
- * Interruptible version of drm_modeset_backoff()
- */
-int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
-{
-	return modeset_backoff(ctx, true);
-}
-EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
-
 /**
  * drm_modeset_lock_init - initialize lock
  * @lock: lock to init
@@ -324,14 +322,18 @@ EXPORT_SYMBOL(drm_modeset_lock_init);
  * deadlock scenario has been detected and it is an error to attempt
  * to take any more locks without first calling drm_modeset_backoff().
  *
+ * If the @ctx is not NULL and initialized with
+ * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with
+ * -ERESTARTSYS when interrupted.
+ *
  * If @ctx is NULL then the function call behaves like a normal,
- * non-nesting mutex_lock() call.
+ * uninterruptible non-nesting mutex_lock() call.
  */
 int drm_modeset_lock(struct drm_modeset_lock *lock,
 		struct drm_modeset_acquire_ctx *ctx)
 {
 	if (ctx)
-		return modeset_lock(lock, ctx, false, false);
+		return modeset_lock(lock, ctx, ctx->interruptible, false);
 
 	ww_mutex_lock(&lock->mutex, NULL);
 	return 0;
@@ -339,21 +341,19 @@ int drm_modeset_lock(struct drm_modeset_lock *lock,
 EXPORT_SYMBOL(drm_modeset_lock);
 
 /**
- * drm_modeset_lock_interruptible - take modeset lock
+ * drm_modeset_lock_single_interruptible - take a single modeset lock
  * @lock: lock to take
- * @ctx: acquire ctx
  *
- * Interruptible version of drm_modeset_lock()
+ * This function behaves as drm_modeset_lock() with a NULL context,
+ * but performs interruptible waits.
+ *
+ * This function returns 0 on success, or -ERESTARTSYS when interrupted.
  */
-int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
-		struct drm_modeset_acquire_ctx *ctx)
+int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)
 {
-	if (ctx)
-		return modeset_lock(lock, ctx, true, false);
-
 	return ww_mutex_lock_interruptible(&lock->mutex, NULL);
 }
-EXPORT_SYMBOL(drm_modeset_lock_interruptible);
+EXPORT_SYMBOL(drm_modeset_lock_single_interruptible);
 
 /**
  * drm_modeset_unlock - drop modeset lock
diff --git a/include/drm/drm_modeset_lock.h b/include/drm/drm_modeset_lock.h
index 4b27c2bb955c..a685d1bb21f2 100644
--- a/include/drm/drm_modeset_lock.h
+++ b/include/drm/drm_modeset_lock.h
@@ -34,6 +34,7 @@ struct drm_modeset_lock;
  * @contended: used internally for -EDEADLK handling
  * @locked: list of held locks
  * @trylock_only: trylock mode used in atomic contexts/panic notifiers
+ * @interruptible: whether interruptible locking should be used.
  *
  * Each thread competing for a set of locks must use one acquire
  * ctx.  And if any lock fxn returns -EDEADLK, it must backoff and
@@ -59,6 +60,9 @@ struct drm_modeset_acquire_ctx {
 	 * Trylock mode, use only for panic handlers!
 	 */
 	bool trylock_only;
+
+	/* Perform interruptible waits on this context. */
+	bool interruptible;
 };
 
 /**
@@ -82,12 +86,13 @@ struct drm_modeset_lock {
 	struct list_head head;
 };
 
+#define DRM_MODESET_ACQUIRE_INTERRUPTIBLE BIT(0)
+
 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
 		uint32_t flags);
 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx);
 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx);
-void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx);
-int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx);
+int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx);
 
 void drm_modeset_lock_init(struct drm_modeset_lock *lock);
 
@@ -111,8 +116,7 @@ static inline bool drm_modeset_is_locked(struct drm_modeset_lock *lock)
 
 int drm_modeset_lock(struct drm_modeset_lock *lock,
 		struct drm_modeset_acquire_ctx *ctx);
-int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
-		struct drm_modeset_acquire_ctx *ctx);
+int __must_check drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock);
 void drm_modeset_unlock(struct drm_modeset_lock *lock);
 
 struct drm_device;
-- 
2.14.1

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[PATCH v2 2/6] drm/atomic: Convert atomic ioctl locking to interruptible.

[Maarten Lankhorst]

Pass DRM_MODESET_ACQUIRE_INTERRUPTIBLE to acquire_init, and
handle drm_modeset_backoff which can now fail by returning the error.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/drm_atomic.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 75f5f74de9bf..366c56fe5f58 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -2234,7 +2234,7 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
 			(arg->flags & DRM_MODE_PAGE_FLIP_EVENT))
 		return -EINVAL;
 
-	drm_modeset_acquire_init(&ctx, 0);
+	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
 
 	state = drm_atomic_state_alloc(dev);
 	if (!state)
@@ -2347,8 +2347,9 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
 
 	if (ret == -EDEADLK) {
 		drm_atomic_state_clear(state);
-		drm_modeset_backoff(&ctx);
-		goto retry;
+		ret = drm_modeset_backoff(&ctx);
+		if (!ret)
+			goto retry;
 	}
 
 	drm_atomic_state_put(state);
-- 
2.14.1

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[PATCH v2 3/6] drm/legacy: Convert cursor ioctl locking to interruptible.

[Maarten Lankhorst]

Pass DRM_MODESET_ACQUIRE_INTERRUPTIBLE to acquire_init, and handle
drm_modeset_backoff which can now fail by returning the error.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/drm_plane.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 7a00351d5b5d..eef58595101c 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -834,7 +834,7 @@ static int drm_mode_cursor_common(struct drm_device *dev,
 		return -ENOENT;
 	}
 
-	drm_modeset_acquire_init(&ctx, 0);
+	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
 retry:
 	ret = drm_modeset_lock(&crtc->mutex, &ctx);
 	if (ret)
@@ -876,8 +876,9 @@ static int drm_mode_cursor_common(struct drm_device *dev,
 	}
 out:
 	if (ret == -EDEADLK) {
-		drm_modeset_backoff(&ctx);
-		goto retry;
+		ret = drm_modeset_backoff(&ctx);
+		if (!ret)
+			goto retry;
 	}
 
 	drm_modeset_drop_locks(&ctx);
-- 
2.14.1

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[PATCH v2 4/6] drm/legacy: Convert setplane ioctl locking to interruptible.

[Maarten Lankhorst]

Pass DRM_MODESET_ACQUIRE_INTERRUPTIBLE to acquire_init, and handle
drm_modeset_backoff which can now fail by returning the error.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/drm_plane.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index eef58595101c..803d67c22da2 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -667,7 +667,7 @@ static int setplane_internal(struct drm_plane *plane,
 	struct drm_modeset_acquire_ctx ctx;
 	int ret;
 
-	drm_modeset_acquire_init(&ctx, 0);
+	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
 retry:
 	ret = drm_modeset_lock_all_ctx(plane->dev, &ctx);
 	if (ret)
@@ -678,8 +678,9 @@ static int setplane_internal(struct drm_plane *plane,
 
 fail:
 	if (ret == -EDEADLK) {
-		drm_modeset_backoff(&ctx);
-		goto retry;
+		ret = drm_modeset_backoff(&ctx);
+		if (!ret)
+			goto retry;
 	}
 	drm_modeset_drop_locks(&ctx);
 	drm_modeset_acquire_fini(&ctx);
-- 
2.14.1

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[PATCH v2 5/6] drm/atomic: Convert pageflip ioctl locking to interruptible.

[Maarten Lankhorst]

Pass DRM_MODESET_ACQUIRE_INTERRUPTIBLE to acquire_init, and handle
drm_modeset_backoff which can now fail by returning the error.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/drm_plane.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index 803d67c22da2..72cba9805edc 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -987,7 +987,7 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 		return -EINVAL;
 	}
 
-	drm_modeset_acquire_init(&ctx, 0);
+	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
 retry:
 	ret = drm_modeset_lock(&crtc->mutex, &ctx);
 	if (ret)
@@ -1076,8 +1076,9 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 	crtc->primary->old_fb = NULL;
 
 	if (ret == -EDEADLK) {
-		drm_modeset_backoff(&ctx);
-		goto retry;
+		ret = drm_modeset_backoff(&ctx);
+		if (!ret)
+			goto retry;
 	}
 
 	drm_modeset_drop_locks(&ctx);
-- 
2.14.1

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[PATCH v2 6/6] drm/crtc: Convert setcrtc ioctl locking to interruptible.

[Maarten Lankhorst]

Pass DRM_MODESET_ACQUIRE_INTERRUPTIBLE to acquire_init, and handle
drm_modeset_backoff which can now fail by returning the error.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/drm_crtc.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 5af25ce5bf7c..68b4e976d5e0 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -577,7 +577,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 	DRM_DEBUG_KMS("[CRTC:%d:%s]\n", crtc->base.id, crtc->name);
 
 	mutex_lock(&crtc->dev->mode_config.mutex);
-	drm_modeset_acquire_init(&ctx, 0);
+	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
 retry:
 	ret = drm_modeset_lock_all_ctx(crtc->dev, &ctx);
 	if (ret)
@@ -717,8 +717,9 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 	kfree(connector_set);
 	drm_mode_destroy(dev, mode);
 	if (ret == -EDEADLK) {
-		drm_modeset_backoff(&ctx);
-		goto retry;
+		ret = drm_modeset_backoff(&ctx);
+		if (!ret)
+			goto retry;
 	}
 	drm_modeset_drop_locks(&ctx);
 	drm_modeset_acquire_fini(&ctx);
-- 
2.14.1

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Re: [PATCH v2 0/6] drm/atomic: Interruptible locks for everyone!

[Maarten Lankhorst]

Op 12-09-17 om 14:41 schreef Maarten Lankhorst:
> drm_atomic_commit could previous have always failed when waits failed,
> but locking was always done uninterruptibly. Add infrastructure to make
> it possible for callers to choose interruptible locking, and convert the
> 5 most common ioctl's to use it.
>
> All other atomic helpers can be converted when additional tests are added
> to kms_atomic_interruptible.
>
> Changes since last version:
> - Small fixes to the preparation patch
> - Convert setcrtc as well.
>
> Maarten Lankhorst (6):
>   drm/atomic: Prepare drm_modeset_lock infrastructure for interruptible
>     waiting, v2.
>   drm/atomic: Convert atomic ioctl locking to interruptible.
>   drm/legacy: Convert cursor ioctl locking to interruptible.
>   drm/legacy: Convert setplane ioctl locking to interruptible.
>   drm/atomic: Convert pageflip ioctl locking to interruptible.
>   drm/crtc: Convert setcrtc ioctl locking to interruptible.
>
>  drivers/gpu/drm/drm_atomic.c       |  7 +--
>  drivers/gpu/drm/drm_crtc.c         |  7 +--
>  drivers/gpu/drm/drm_debugfs_crc.c  |  2 +-
>  drivers/gpu/drm/drm_modeset_lock.c | 96 +++++++++++++++++++-------------------
>  drivers/gpu/drm/drm_plane.c        | 21 +++++----
>  include/drm/drm_modeset_lock.h     | 12 +++--
>  6 files changed, 77 insertions(+), 68 deletions(-)
>
Please ignore this series, should have been sent to dri-devel with intel-gfx to cc. I'm resending.

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[PATCH v2 1/6] drm/atomic: Prepare drm_modeset_lock infrastructure for interruptible waiting, v2.

[Maarten Lankhorst]

When we want to make drm_atomic_commit interruptible, there are a lot of
places that call the lock function, which we don't have control over.

Rather than trying to convert every single one, it's easier to toggle
interruptible waiting per acquire_ctx. If drm_modeset_acquire_init is
called with DRM_MODESET_ACQUIRE_INTERRUPTIBLE, then we will perform
interruptible waits in drm_modeset_lock and drm_modeset_backoff.

Changes since v1:
- Fix locking example in drm_modeset_lock.c to be compatible
  with interruptible waiting (xexaxo) and make it default.
  Uninterruptible waiting shouldn't happen except in corner cases,
  but the example will still apply if the flag is removed.
- Add drm_modeset_lock_single_interruptible() to documentation.
- Fix dead link to removed drm_modeset_lock_interruptible() in
  drm_modeset_lock().

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> #v1
Cc: Emil Velikov <emil.l.velikov@gmail.com>
---
 drivers/gpu/drm/drm_debugfs_crc.c  |  2 +-
 drivers/gpu/drm/drm_modeset_lock.c | 96 +++++++++++++++++++-------------------
 include/drm/drm_modeset_lock.h     | 12 +++--
 3 files changed, 57 insertions(+), 53 deletions(-)

diff --git a/drivers/gpu/drm/drm_debugfs_crc.c b/drivers/gpu/drm/drm_debugfs_crc.c
index f9e26dda56d6..9dd879589a2c 100644
--- a/drivers/gpu/drm/drm_debugfs_crc.c
+++ b/drivers/gpu/drm/drm_debugfs_crc.c
@@ -155,7 +155,7 @@ static int crtc_crc_open(struct inode *inode, struct file *filep)
 	int ret = 0;
 
 	if (drm_drv_uses_atomic_modeset(crtc->dev)) {
-		ret = drm_modeset_lock_interruptible(&crtc->mutex, NULL);
+		ret = drm_modeset_lock_single_interruptible(&crtc->mutex);
 		if (ret)
 			return ret;
 
diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
index af4e906c630d..e123497da0ca 100644
--- a/drivers/gpu/drm/drm_modeset_lock.c
+++ b/drivers/gpu/drm/drm_modeset_lock.c
@@ -39,23 +39,28 @@
  *
  * The basic usage pattern is to::
  *
- *     drm_modeset_acquire_init(&ctx)
+ *     drm_modeset_acquire_init(ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
  *     retry:
  *     foreach (lock in random_ordered_set_of_locks) {
- *         ret = drm_modeset_lock(lock, &ctx)
+ *         ret = drm_modeset_lock(lock, ctx)
  *         if (ret == -EDEADLK) {
- *             drm_modeset_backoff(&ctx);
- *             goto retry;
+ *             ret = drm_modeset_backoff(ctx);
+ *             if (!ret)
+ *                 goto retry;
  *         }
+ *         if (ret)
+ *             goto out;
  *     }
  *     ... do stuff ...
- *     drm_modeset_drop_locks(&ctx);
- *     drm_modeset_acquire_fini(&ctx);
+ *     out:
+ *     drm_modeset_drop_locks(ctx);
+ *     drm_modeset_acquire_fini(ctx);
  *
  * If all that is needed is a single modeset lock, then the &struct
  * drm_modeset_acquire_ctx is not needed and the locking can be simplified
- * by passing a NULL instead of ctx in the drm_modeset_lock()
- * call and, when done, by calling drm_modeset_unlock().
+ * by passing a NULL instead of ctx in the drm_modeset_lock() call or
+ * calling  drm_modeset_lock_single_interruptible(). To unlock afterwards
+ * call drm_modeset_unlock().
  *
  * On top of these per-object locks using &ww_mutex there's also an overall
  * &drm_mode_config.mutex, for protecting everything else. Mostly this means
@@ -178,7 +183,11 @@ EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
 /**
  * drm_modeset_acquire_init - initialize acquire context
  * @ctx: the acquire context
- * @flags: for future
+ * @flags: 0 or %DRM_MODESET_ACQUIRE_INTERRUPTIBLE
+ *
+ * When passing %DRM_MODESET_ACQUIRE_INTERRUPTIBLE to @flags,
+ * all calls to drm_modeset_lock() will perform an interruptible
+ * wait.
  */
 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
 		uint32_t flags)
@@ -186,6 +195,9 @@ void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
 	memset(ctx, 0, sizeof(*ctx));
 	ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
 	INIT_LIST_HEAD(&ctx->locked);
+
+	if (flags & DRM_MODESET_ACQUIRE_INTERRUPTIBLE)
+		ctx->interruptible = true;
 }
 EXPORT_SYMBOL(drm_modeset_acquire_init);
 
@@ -261,8 +273,19 @@ static inline int modeset_lock(struct drm_modeset_lock *lock,
 	return ret;
 }
 
-static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
-		bool interruptible)
+/**
+ * drm_modeset_backoff - deadlock avoidance backoff
+ * @ctx: the acquire context
+ *
+ * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
+ * you must call this function to drop all currently held locks and
+ * block until the contended lock becomes available.
+ *
+ * This function returns 0 on success, or -ERESTARTSYS if this context
+ * is initialized with %DRM_MODESET_ACQUIRE_INTERRUPTIBLE and the
+ * wait has been interrupted.
+ */
+int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
 {
 	struct drm_modeset_lock *contended = ctx->contended;
 
@@ -273,35 +296,10 @@ static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
 
 	drm_modeset_drop_locks(ctx);
 
-	return modeset_lock(contended, ctx, interruptible, true);
-}
-
-/**
- * drm_modeset_backoff - deadlock avoidance backoff
- * @ctx: the acquire context
- *
- * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
- * you must call this function to drop all currently held locks and
- * block until the contended lock becomes available.
- */
-void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
-{
-	modeset_backoff(ctx, false);
+	return modeset_lock(contended, ctx, ctx->interruptible, true);
 }
 EXPORT_SYMBOL(drm_modeset_backoff);
 
-/**
- * drm_modeset_backoff_interruptible - deadlock avoidance backoff
- * @ctx: the acquire context
- *
- * Interruptible version of drm_modeset_backoff()
- */
-int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
-{
-	return modeset_backoff(ctx, true);
-}
-EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
-
 /**
  * drm_modeset_lock_init - initialize lock
  * @lock: lock to init
@@ -324,14 +322,18 @@ EXPORT_SYMBOL(drm_modeset_lock_init);
  * deadlock scenario has been detected and it is an error to attempt
  * to take any more locks without first calling drm_modeset_backoff().
  *
+ * If the @ctx is not NULL and initialized with
+ * %DRM_MODESET_ACQUIRE_INTERRUPTIBLE, this function will fail with
+ * -ERESTARTSYS when interrupted.
+ *
  * If @ctx is NULL then the function call behaves like a normal,
- * non-nesting mutex_lock() call.
+ * uninterruptible non-nesting mutex_lock() call.
  */
 int drm_modeset_lock(struct drm_modeset_lock *lock,
 		struct drm_modeset_acquire_ctx *ctx)
 {
 	if (ctx)
-		return modeset_lock(lock, ctx, false, false);
+		return modeset_lock(lock, ctx, ctx->interruptible, false);
 
 	ww_mutex_lock(&lock->mutex, NULL);
 	return 0;
@@ -339,21 +341,19 @@ int drm_modeset_lock(struct drm_modeset_lock *lock,
 EXPORT_SYMBOL(drm_modeset_lock);
 
 /**
- * drm_modeset_lock_interruptible - take modeset lock
+ * drm_modeset_lock_single_interruptible - take a single modeset lock
  * @lock: lock to take
- * @ctx: acquire ctx
  *
- * Interruptible version of drm_modeset_lock()
+ * This function behaves as drm_modeset_lock() with a NULL context,
+ * but performs interruptible waits.
+ *
+ * This function returns 0 on success, or -ERESTARTSYS when interrupted.
  */
-int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
-		struct drm_modeset_acquire_ctx *ctx)
+int drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock)
 {
-	if (ctx)
-		return modeset_lock(lock, ctx, true, false);
-
 	return ww_mutex_lock_interruptible(&lock->mutex, NULL);
 }
-EXPORT_SYMBOL(drm_modeset_lock_interruptible);
+EXPORT_SYMBOL(drm_modeset_lock_single_interruptible);
 
 /**
  * drm_modeset_unlock - drop modeset lock
diff --git a/include/drm/drm_modeset_lock.h b/include/drm/drm_modeset_lock.h
index 4b27c2bb955c..a685d1bb21f2 100644
--- a/include/drm/drm_modeset_lock.h
+++ b/include/drm/drm_modeset_lock.h
@@ -34,6 +34,7 @@ struct drm_modeset_lock;
  * @contended: used internally for -EDEADLK handling
  * @locked: list of held locks
  * @trylock_only: trylock mode used in atomic contexts/panic notifiers
+ * @interruptible: whether interruptible locking should be used.
  *
  * Each thread competing for a set of locks must use one acquire
  * ctx.  And if any lock fxn returns -EDEADLK, it must backoff and
@@ -59,6 +60,9 @@ struct drm_modeset_acquire_ctx {
 	 * Trylock mode, use only for panic handlers!
 	 */
 	bool trylock_only;
+
+	/* Perform interruptible waits on this context. */
+	bool interruptible;
 };
 
 /**
@@ -82,12 +86,13 @@ struct drm_modeset_lock {
 	struct list_head head;
 };
 
+#define DRM_MODESET_ACQUIRE_INTERRUPTIBLE BIT(0)
+
 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
 		uint32_t flags);
 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx);
 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx);
-void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx);
-int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx);
+int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx);
 
 void drm_modeset_lock_init(struct drm_modeset_lock *lock);
 
@@ -111,8 +116,7 @@ static inline bool drm_modeset_is_locked(struct drm_modeset_lock *lock)
 
 int drm_modeset_lock(struct drm_modeset_lock *lock,
 		struct drm_modeset_acquire_ctx *ctx);
-int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
-		struct drm_modeset_acquire_ctx *ctx);
+int __must_check drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock);
 void drm_modeset_unlock(struct drm_modeset_lock *lock);
 
 struct drm_device;
-- 
2.14.1

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Re: [PATCH v2 1/6] drm/atomic: Prepare drm_modeset_lock infrastructure for interruptible waiting, v2.

[Emil Velikov]

On 12 September 2017 at 14:37, Maarten Lankhorst
<maarten.lankhorst@linux.intel.com> wrote:
> When we want to make drm_atomic_commit interruptible, there are a lot of
> places that call the lock function, which we don't have control over.
>
> Rather than trying to convert every single one, it's easier to toggle
> interruptible waiting per acquire_ctx. If drm_modeset_acquire_init is
> called with DRM_MODESET_ACQUIRE_INTERRUPTIBLE, then we will perform
> interruptible waits in drm_modeset_lock and drm_modeset_backoff.
>
> Changes since v1:
> - Fix locking example in drm_modeset_lock.c to be compatible
>   with interruptible waiting (xexaxo) and make it default.
>   Uninterruptible waiting shouldn't happen except in corner cases,
>   but the example will still apply if the flag is removed.
> - Add drm_modeset_lock_single_interruptible() to documentation.
> - Fix dead link to removed drm_modeset_lock_interruptible() in
>   drm_modeset_lock().
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> #v1
> Cc: Emil Velikov <emil.l.velikov@gmail.com>
Thanks for the documentation updates/fixes Maarten. FWIW the series is
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>

-Emil
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Re: [PATCH v2 1/6] drm/atomic: Prepare drm_modeset_lock infrastructure for interruptible waiting, v2.

[Maarten Lankhorst]

Op 12-09-17 om 15:56 schreef Emil Velikov:
> On 12 September 2017 at 14:37, Maarten Lankhorst
> <maarten.lankhorst@linux.intel.com> wrote:
>> When we want to make drm_atomic_commit interruptible, there are a lot of
>> places that call the lock function, which we don't have control over.
>>
>> Rather than trying to convert every single one, it's easier to toggle
>> interruptible waiting per acquire_ctx. If drm_modeset_acquire_init is
>> called with DRM_MODESET_ACQUIRE_INTERRUPTIBLE, then we will perform
>> interruptible waits in drm_modeset_lock and drm_modeset_backoff.
>>
>> Changes since v1:
>> - Fix locking example in drm_modeset_lock.c to be compatible
>>   with interruptible waiting (xexaxo) and make it default.
>>   Uninterruptible waiting shouldn't happen except in corner cases,
>>   but the example will still apply if the flag is removed.
>> - Add drm_modeset_lock_single_interruptible() to documentation.
>> - Fix dead link to removed drm_modeset_lock_interruptible() in
>>   drm_modeset_lock().
>>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> #v1
>> Cc: Emil Velikov <emil.l.velikov@gmail.com>
> Thanks for the documentation updates/fixes Maarten. FWIW the series is
> Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
>
> -Emil

Thanks, applied. :)

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