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71 lines
2.4 KiB
Diff
71 lines
2.4 KiB
Diff
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From 8218c3f4df3bb1c637c17552405039a6dd3c1ee1 Mon Sep 17 00:00:00 2001
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From: Daniel Vetter <daniel.vetter@ffwll.ch>
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Date: Fri, 27 Feb 2015 12:58:13 +0100
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Subject: drm: Fixup racy refcounting in plane_force_disable
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Originally it was impossible to be dropping the last refcount in this
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function since there was always one around still from the idr. But in
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commit 83f45fc360c8e16a330474860ebda872d1384c8c
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Author: Daniel Vetter <daniel.vetter@ffwll.ch>
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Date: Wed Aug 6 09:10:18 2014 +0200
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drm: Don't grab an fb reference for the idr
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we've switched to weak references, broke that assumption but forgot to
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fix it up.
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Since we still force-disable planes it's only possible to hit this
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when racing multiple rmfb with fbdev restoring or similar evil things.
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As long as userspace is nice it's impossible to hit the BUG_ON.
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But the BUG_ON would most likely be hit from fbdev code, which usually
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invovles the console_lock besides all modeset locks. So very likely
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we'd never get the bug reports if this was hit in the wild, hence
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better be safe than sorry and backport.
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Spotted by Matt Roper while reviewing other patches.
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[airlied: pull this back into 4.0 - the oops happens there]
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Cc: stable@vger.kernel.org
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Cc: Matt Roper <matthew.d.roper@intel.com>
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Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
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Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
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Signed-off-by: Dave Airlie <airlied@redhat.com>
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diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
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index f6d04c7..679b10e 100644
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--- a/drivers/gpu/drm/drm_crtc.c
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+++ b/drivers/gpu/drm/drm_crtc.c
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@@ -525,17 +525,6 @@ void drm_framebuffer_reference(struct drm_framebuffer *fb)
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}
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EXPORT_SYMBOL(drm_framebuffer_reference);
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-static void drm_framebuffer_free_bug(struct kref *kref)
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-{
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- BUG();
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-}
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-
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-static void __drm_framebuffer_unreference(struct drm_framebuffer *fb)
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-{
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- DRM_DEBUG("%p: FB ID: %d (%d)\n", fb, fb->base.id, atomic_read(&fb->refcount.refcount));
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- kref_put(&fb->refcount, drm_framebuffer_free_bug);
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-}
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-
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/**
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* drm_framebuffer_unregister_private - unregister a private fb from the lookup idr
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* @fb: fb to unregister
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@@ -1320,7 +1309,7 @@ void drm_plane_force_disable(struct drm_plane *plane)
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return;
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}
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/* disconnect the plane from the fb and crtc: */
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- __drm_framebuffer_unreference(plane->old_fb);
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+ drm_framebuffer_unreference(plane->old_fb);
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plane->old_fb = NULL;
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plane->fb = NULL;
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plane->crtc = NULL;
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--
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