From: Daniel Vetter <daniel.vetter-/w4YWyX8dFk@public.gmane.org>
To: DRI Development
<dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org>
Cc: Nouveau Dev
<nouveau-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org>,
Intel Graphics Development
<intel-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org>,
Radeon Dev
<xorg-driver-ati-go0+a7rfsptAfugRpC6u6w@public.gmane.org>,
Daniel Vetter <daniel.vetter-/w4YWyX8dFk@public.gmane.org>
Subject: [PATCH 32/37] drm: optimize drm_framebuffer_remove
Date: Wed, 12 Dec 2012 14:07:12 +0100 [thread overview]
Message-ID: <1355317637-16742-33-git-send-email-daniel.vetter@ffwll.ch> (raw)
In-Reply-To: <1355317637-16742-1-git-send-email-daniel.vetter-/w4YWyX8dFk@public.gmane.org>
Now that all framebuffer usage is properly refcounted, we are no
longer required to hold the modeset locks while dropping the last
reference. Hence implemented a fastpath which avoids the potential
stalls associated with grabbing mode_config.lock for the case where
there's no other reference around.
Explain in a big comment why it is safe. Also update kerneldocs with
the new locking rules around drm_framebuffer_remove.
Signed-off-by: Daniel Vetter <daniel.vetter-/w4YWyX8dFk@public.gmane.org>
---
drivers/gpu/drm/drm_crtc.c | 72 +++++++++++++++++++++++++++-----------------
1 file changed, 45 insertions(+), 27 deletions(-)
diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 6562eba..6dd441c 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -516,7 +516,11 @@ EXPORT_SYMBOL(drm_framebuffer_cleanup);
*
* Scans all the CRTCs and planes in @dev's mode_config. If they're
* using @fb, removes it, setting it to NULL. Then drops the reference to the
- * passed-in framebuffer.
+ * passed-in framebuffer. Might take the modeset locks.
+ *
+ * Note that this function optimizes the cleanup away if the caller holds the
+ * last reference to the framebuffer. It is also guaranteed to not take the
+ * modeset locks in this case.
*/
void drm_framebuffer_remove(struct drm_framebuffer *fb)
{
@@ -526,33 +530,51 @@ void drm_framebuffer_remove(struct drm_framebuffer *fb)
struct drm_mode_set set;
int ret;
- WARN_ON(!drm_modeset_is_locked(dev));
WARN_ON(!list_empty(&fb->filp_head));
- /* remove from any CRTC */
- list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {
- if (crtc->fb == fb) {
- /* should turn off the crtc */
- memset(&set, 0, sizeof(struct drm_mode_set));
- set.crtc = crtc;
- set.fb = NULL;
- ret = drm_mode_set_config_internal(&set);
- if (ret)
- DRM_ERROR("failed to reset crtc %p when fb was deleted\n", crtc);
+ /*
+ * drm ABI mandates that we remove any deleted framebuffers from active
+ * useage. But since most sane clients only remove framebuffers they no
+ * longer need, try to optimize this away.
+ *
+ * Since we're holding a reference ourselves, observing a refcount of 1
+ * means that we're the last holder and can skip it. Also, the refcount
+ * can never increase from 1 again, so we don't need any barriers or
+ * locks.
+ *
+ * Note that userspace could try to race with use and instate a new
+ * usage _after_ we've cleared all current ones. End result will be an
+ * in-use fb with fb-id == 0. Userspace is allowed to shoot its own foot
+ * in this manner.
+ */
+ if (atomic_read(&fb->refcount.refcount) > 1) {
+ drm_modeset_lock_all(dev);
+ /* remove from any CRTC */
+ list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {
+ if (crtc->fb == fb) {
+ /* should turn off the crtc */
+ memset(&set, 0, sizeof(struct drm_mode_set));
+ set.crtc = crtc;
+ set.fb = NULL;
+ ret = drm_mode_set_config_internal(&set);
+ if (ret)
+ DRM_ERROR("failed to reset crtc %p when fb was deleted\n", crtc);
+ }
}
- }
- list_for_each_entry(plane, &dev->mode_config.plane_list, head) {
- if (plane->fb == fb) {
- /* should turn off the crtc */
- ret = plane->funcs->disable_plane(plane);
- if (ret)
- DRM_ERROR("failed to disable plane with busy fb\n");
- /* disconnect the plane from the fb and crtc: */
- __drm_framebuffer_unreference(plane->fb);
- plane->fb = NULL;
- plane->crtc = NULL;
+ list_for_each_entry(plane, &dev->mode_config.plane_list, head) {
+ if (plane->fb == fb) {
+ /* should turn off the crtc */
+ ret = plane->funcs->disable_plane(plane);
+ if (ret)
+ DRM_ERROR("failed to disable plane with busy fb\n");
+ /* disconnect the plane from the fb and crtc: */
+ __drm_framebuffer_unreference(plane->fb);
+ plane->fb = NULL;
+ plane->crtc = NULL;
+ }
}
+ drm_modeset_unlock_all(dev);
}
drm_framebuffer_unreference(fb);
@@ -2537,9 +2559,7 @@ int drm_mode_rmfb(struct drm_device *dev,
mutex_unlock(&dev->mode_config.fb_lock);
mutex_unlock(&file_priv->fbs_lock);
- drm_modeset_lock_all(dev);
drm_framebuffer_remove(fb);
- drm_modeset_unlock_all(dev);
return 0;
@@ -2687,9 +2707,7 @@ void drm_fb_release(struct drm_file *priv)
list_del_init(&fb->filp_head);
/* This will also drop the fpriv->fbs reference. */
- drm_modeset_lock_all(dev);
drm_framebuffer_remove(fb);
- drm_modeset_unlock_all(dev);
}
mutex_unlock(&priv->fbs_lock);
}
--
1.7.10.4
next prev parent reply other threads:[~2012-12-12 13:07 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-12 13:06 [PATCH 00/37] [RFC] revamped modeset locking Daniel Vetter
2012-12-12 13:06 ` [PATCH 01/37] drm: review locking rules in drm_crtc.c Daniel Vetter
2012-12-12 13:06 ` [PATCH 05/37] drm/i915: use drm_modeset_lock_all Daniel Vetter
2012-12-12 13:06 ` [PATCH 08/37] drm/shmobile: " Daniel Vetter
2012-12-12 13:06 ` [PATCH 10/37] drm: add per-crtc locks Daniel Vetter
2012-12-13 11:38 ` [Intel-gfx] " Ville Syrjälä
2012-12-13 11:54 ` Daniel Vetter
2012-12-13 14:25 ` Ville Syrjälä
2012-12-12 13:06 ` [PATCH 11/37] drm/radeon: add W|RREG32_IDX for MM_INDEX|DATA based mmio accesss Daniel Vetter
2012-12-12 13:07 ` [PATCH 25/37] drm: don't take modeset locks in getfb ioctl Daniel Vetter
2012-12-12 13:07 ` [PATCH 26/37] drm: fb refcounting for dirtyfb_ioctl Daniel Vetter
2012-12-12 13:07 ` [PATCH 31/37] drm/vmwgfx: add proper framebuffer refcounting Daniel Vetter
2012-12-12 13:07 ` [PATCH 33/37] drm/nouveau: try to protect nbo->pin_refcount Daniel Vetter
[not found] ` <1355317637-16742-1-git-send-email-daniel.vetter-/w4YWyX8dFk@public.gmane.org>
2012-12-12 13:06 ` [PATCH 02/37] drm/doc: integrate drm_crtc.c kerneldoc Daniel Vetter
2012-12-12 13:06 ` [PATCH 03/37] drm: add drm_modeset_lock|unlock_all Daniel Vetter
2012-12-12 13:06 ` [PATCH 04/37] drm/i915: rework locking for intel_dpio|sbi_read|write Daniel Vetter
2012-12-12 20:54 ` [Intel-gfx] " Jesse Barnes
2012-12-12 22:00 ` Daniel Vetter
2012-12-12 22:05 ` Jesse Barnes
2012-12-12 13:06 ` [PATCH 06/37] drm/gma500: use drm_modeset_lock_all Daniel Vetter
2012-12-12 13:06 ` [PATCH 07/37] drm/ast: " Daniel Vetter
2012-12-12 13:06 ` [PATCH 09/37] drm/vmgfx: " Daniel Vetter
2012-12-12 13:06 ` [PATCH 12/37] drm/radeon: make indirect register access concurrency-safe Daniel Vetter
2012-12-12 13:06 ` [PATCH 13/37] drm/nouveau: protect evo_wait/evo_kick sections with a channel mutex Daniel Vetter
2012-12-12 13:06 ` [PATCH 14/37] drm: only take the crtc lock for ->cursor_set Daniel Vetter
2012-12-12 13:06 ` [PATCH 15/37] drm: only take the crtc lock for ->cursor_move Daniel Vetter
2012-12-13 11:03 ` [PATCH] " Daniel Vetter
2012-12-12 13:06 ` [PATCH 16/37] drm/<drivers>: reorder framebuffer init sequence Daniel Vetter
2012-12-13 11:05 ` [PATCH 1/2] " Daniel Vetter
[not found] ` <1355396719-25286-1-git-send-email-daniel.vetter-/w4YWyX8dFk@public.gmane.org>
2012-12-13 11:05 ` [PATCH 2/2] drm/exynos: " Daniel Vetter
2012-12-13 12:26 ` Inki Dae
2012-12-13 12:43 ` Daniel Vetter
2012-12-13 15:16 ` Inki Dae
2012-12-13 16:38 ` Daniel Vetter
2012-12-14 4:57 ` Inki Dae
2012-12-14 8:40 ` Daniel Vetter
2012-12-12 13:06 ` [PATCH 17/37] drm: revamp locking around fb creation/destruction Daniel Vetter
2012-12-12 13:06 ` [PATCH 18/37] drm: create drm_framebuffer_lookup Daniel Vetter
2012-12-12 13:06 ` [PATCH 19/37] drm/gma500: move fbcon restore to lastclose Daniel Vetter
2012-12-12 13:07 ` [PATCH 20/37] drm: revamp framebuffer cleanup interfaces Daniel Vetter
2012-12-12 13:07 ` [PATCH 21/37] drm: reference framebuffers which are on the idr Daniel Vetter
2012-12-12 13:07 ` [PATCH 22/37] drm: nest modeset locks within fpriv->fbs_lock Daniel Vetter
2012-12-12 13:07 ` [PATCH 23/37] drm/i915: fixup overlay stolen memory leak Daniel Vetter
2012-12-12 13:07 ` [PATCH 24/37] drm: push modeset_lock_all into ->fb_create driver callbacks Daniel Vetter
2012-12-12 13:07 ` [PATCH 27/37] drm: refcounting for sprite framebuffers Daniel Vetter
2012-12-12 13:07 ` [PATCH 28/37] drm: encapsulate crtc->set_config calls Daniel Vetter
2012-12-12 13:07 ` [PATCH 29/37] drm: refcounting for crtc framebuffers Daniel Vetter
2012-12-12 13:07 ` [PATCH 30/37] drm/i915: dump refcount into framebuffer debugfs file Daniel Vetter
2012-12-12 13:07 ` Daniel Vetter [this message]
2012-12-12 13:07 ` [PATCH 34/37] drm/ttm: fix fence locking in ttm_buffer_object_transfer Daniel Vetter
2012-12-12 14:48 ` Jerome Glisse
[not found] ` <CAH3drwbL34+omj2S3ArOPgoYRQ3uzPEiRPFLn7YkP3cOMnPiZg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2012-12-12 15:42 ` Daniel Vetter
2012-12-13 11:06 ` [PATCH] allow shmob+imx drm drivers to be compiled Daniel Vetter
2012-12-13 11:18 ` Daniel Vetter
2012-12-13 11:26 ` [PATCH] drm/ttm: fix fence locking in ttm_buffer_object_transfer Daniel Vetter
2012-12-12 13:07 ` [PATCH 35/37] drm/radeon: fix fence locking in the pageflip callback Daniel Vetter
2012-12-12 13:07 ` [PATCH 36/37] drm: only grab the crtc lock for pageflips Daniel Vetter
2012-12-12 13:07 ` [PATCH 37/37] drm: don't hold crtc mutexes for connector ->detect callbacks Daniel Vetter
2012-12-12 14:18 ` [PATCH 00/37] [RFC] revamped modeset locking Daniel Vetter
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