Re: [Intel-gfx] [PATCH] drm/core: Do not preserve framebuffer on rmfb, v4.

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, May 05, 2016 at 10:07:57AM +0100, Tvrtko Ursulin wrote:
> 
> On 04/05/16 13:38, Maarten Lankhorst wrote:
> >It turns out that preserving framebuffers after the rmfb call breaks
> >vmwgfx userspace. This was originally introduced because it was thought
> >nobody relied on the behavior, but unfortunately it seems there are
> >exceptions.
> >
> >drm_framebuffer_remove may fail with -EINTR now, so a straight revert
> >is impossible. There is no way to remove the framebuffer from the lists
> >and active planes without introducing a race because of the different
> >locking requirements. Instead call drm_framebuffer_remove from a
> >workqueue, which is unaffected by signals.
> >
> >Changes since v1:
> >- Add comment.
> >Changes since v2:
> >- Add fastpath for refcount = 1. (danvet)
> >Changes since v3:
> >- Rebased.
> >- Restore lastclose framebuffer removal too.
> >
> >Cc: stable@vger.kernel.org #v4.4+
> >Fixes: 13803132818c ("drm/core: Preserve the framebuffer after removing it.")
> >Testcase: kms_rmfb_basic
> >References: https://lists.freedesktop.org/archives/dri-devel/2016-March/102876.html
> >Cc: Thomas Hellstrom <thellstrom@vmware.com>
> >Cc: David Herrmann <dh.herrmann@gmail.com>
> >Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> >Tested-by: Thomas Hellstrom <thellstrom@vmware.com> #v3
> 
> Can't be 100% since apparently eDP regressed a lot recently for me, but
> seems to be effective in getting rid of stale planes in my test cases.
> 
> Tested-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Applied to drm-misc, thanks.
-Daniel

> 
> Regards,
> 
> Tvrtko
> 
> >---
> >  drivers/gpu/drm/drm_crtc.c | 63 ++++++++++++++++++++++++++++++++++++++++------
> >  1 file changed, 56 insertions(+), 7 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> >index 9626a0cc050a..9a3d17b70091 100644
> >--- a/drivers/gpu/drm/drm_crtc.c
> >+++ b/drivers/gpu/drm/drm_crtc.c
> >@@ -3440,6 +3440,24 @@ int drm_mode_addfb2(struct drm_device *dev,
> >  	return 0;
> >  }
> >
> >+struct drm_mode_rmfb_work {
> >+	struct work_struct work;
> >+	struct list_head fbs;
> >+};
> >+
> >+static void drm_mode_rmfb_work_fn(struct work_struct *w)
> >+{
> >+	struct drm_mode_rmfb_work *arg = container_of(w, typeof(*arg), work);
> >+
> >+	while (!list_empty(&arg->fbs)) {
> >+		struct drm_framebuffer *fb =
> >+			list_first_entry(&arg->fbs, typeof(*fb), filp_head);
> >+
> >+		list_del_init(&fb->filp_head);
> >+		drm_framebuffer_remove(fb);
> >+	}
> >+}
> >+
> >  /**
> >   * drm_mode_rmfb - remove an FB from the configuration
> >   * @dev: drm device for the ioctl
> >@@ -3480,12 +3498,29 @@ int drm_mode_rmfb(struct drm_device *dev,
> >  	list_del_init(&fb->filp_head);
> >  	mutex_unlock(&file_priv->fbs_lock);
> >
> >-	/* we now own the reference that was stored in the fbs list */
> >-	drm_framebuffer_unreference(fb);
> >-
> >  	/* drop the reference we picked up in framebuffer lookup */
> >  	drm_framebuffer_unreference(fb);
> >
> >+	/*
> >+	 * we now own the reference that was stored in the fbs list
> >+	 *
> >+	 * drm_framebuffer_remove may fail with -EINTR on pending signals,
> >+	 * so run this in a separate stack as there's no way to correctly
> >+	 * handle this after the fb is already removed from the lookup table.
> >+	 */
> >+	if (drm_framebuffer_read_refcount(fb) > 1) {
> >+		struct drm_mode_rmfb_work arg;
> >+
> >+		INIT_WORK_ONSTACK(&arg.work, drm_mode_rmfb_work_fn);
> >+		INIT_LIST_HEAD(&arg.fbs);
> >+		list_add_tail(&fb->filp_head, &arg.fbs);
> >+
> >+		schedule_work(&arg.work);
> >+		flush_work(&arg.work);
> >+		destroy_work_on_stack(&arg.work);
> >+	} else
> >+		drm_framebuffer_unreference(fb);
> >+
> >  	return 0;
> >
> >  fail_unref:
> >@@ -3635,7 +3670,6 @@ out_err1:
> >  	return ret;
> >  }
> >
> >-
> >  /**
> >   * drm_fb_release - remove and free the FBs on this file
> >   * @priv: drm file for the ioctl
> >@@ -3650,6 +3684,9 @@ out_err1:
> >  void drm_fb_release(struct drm_file *priv)
> >  {
> >  	struct drm_framebuffer *fb, *tfb;
> >+	struct drm_mode_rmfb_work arg;
> >+
> >+	INIT_LIST_HEAD(&arg.fbs);
> >
> >  	/*
> >  	 * When the file gets released that means no one else can access the fb
> >@@ -3662,10 +3699,22 @@ void drm_fb_release(struct drm_file *priv)
> >  	 * at it any more.
> >  	 */
> >  	list_for_each_entry_safe(fb, tfb, &priv->fbs, filp_head) {
> >-		list_del_init(&fb->filp_head);
> >+		if (drm_framebuffer_read_refcount(fb) > 1) {
> >+			list_move_tail(&fb->filp_head, &arg.fbs);
> >+		} else {
> >+			list_del_init(&fb->filp_head);
> >
> >-		/* This drops the fpriv->fbs reference. */
> >-		drm_framebuffer_unreference(fb);
> >+			/* This drops the fpriv->fbs reference. */
> >+			drm_framebuffer_unreference(fb);
> >+		}
> >+	}
> >+
> >+	if (!list_empty(&arg.fbs)) {
> >+		INIT_WORK_ONSTACK(&arg.work, drm_mode_rmfb_work_fn);
> >+
> >+		schedule_work(&arg.work);
> >+		flush_work(&arg.work);
> >+		destroy_work_on_stack(&arg.work);
> >  	}
> >  }
> >
> >
> _______________________________________________
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> Intel-gfx@lists.freedesktop.org
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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