From b3a38998f042b862f5ba4d7f2268f3a8dfb4883a Mon Sep 17 00:00:00 2001 From: Nick Hoath Date: Thu, 19 Feb 2015 16:30:47 +0000 Subject: [PATCH] drm/i915: Fix a use after free, and unbalanced refcounting When converting from implicitly tracked execlist queue items to ref counted requests, not all frees of requests were replaced with unrefs, and extraneous refs/unrefs of contexts were added. Correct the unbalanced refcount & replace the frees. Remove a noisy warning when hitting the request creation path. drm_i915_gem_request and intel_context are both kref reference counted structures. Upon allocation, drm_i915_gem_request's ref count should be bumped using kref_init. When a context is assigned to the request, the context's reference count should be bumped using i915_gem_context_reference. i915_gem_request_reference will reduce the context reference count when the request is freed. Problem introduced in commit 6d3d8274bc45de4babb62d64562d92af984dd238 Author: Nick Hoath AuthorDate: Thu Jan 15 13:10:39 2015 +0000 drm/i915: Subsume intel_ctx_submit_request in to drm_i915_gem_request v2: Added comments explaining how the ctx pointer and the request object should be ref-counted. Removed noisy warning. v3: Cleaned up the language used in the commit & the header description (Thanks David Gordon) Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88652 Signed-off-by: Nick Hoath Reviewed-by: Thomas Daniel Reviewed-by: Daniel Vetter Signed-off-by: Jani Nikula --- drivers/gpu/drm/i915/i915_drv.h | 14 +++++++++++++- drivers/gpu/drm/i915/i915_gem.c | 3 +-- drivers/gpu/drm/i915/intel_lrc.c | 8 ++++---- 3 files changed, 18 insertions(+), 7 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index b38c770a22f5..8727086cf48c 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -2114,6 +2114,9 @@ void i915_gem_track_fb(struct drm_i915_gem_object *old, * number comparisons on buffer last_read|write_seqno. It also allows an * emission time to be associated with the request for tracking how far ahead * of the GPU the submission is. + * + * The requests are reference counted, so upon creation they should have an + * initial reference taken using kref_init */ struct drm_i915_gem_request { struct kref ref; @@ -2137,7 +2140,16 @@ struct drm_i915_gem_request { /** Position in the ringbuffer of the end of the whole request */ u32 tail; - /** Context related to this request */ + /** + * Context related to this request + * Contexts are refcounted, so when this request is associated with a + * context, we must increment the context's refcount, to guarantee that + * it persists while any request is linked to it. Requests themselves + * are also refcounted, so the request will only be freed when the last + * reference to it is dismissed, and the code in + * i915_gem_request_free() will then decrement the refcount on the + * context. + */ struct intel_context *ctx; /** Batch buffer related to this request if any */ diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index c26d36cc4b31..e5daad5f75fb 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2659,8 +2659,7 @@ static void i915_gem_reset_ring_cleanup(struct drm_i915_private *dev_priv, if (submit_req->ctx != ring->default_context) intel_lr_context_unpin(ring, submit_req->ctx); - i915_gem_context_unreference(submit_req->ctx); - kfree(submit_req); + i915_gem_request_unreference(submit_req); } /* diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c index 0f358c5999ec..e8d3da9f3373 100644 --- a/drivers/gpu/drm/i915/intel_lrc.c +++ b/drivers/gpu/drm/i915/intel_lrc.c @@ -503,18 +503,19 @@ static int execlists_context_queue(struct intel_engine_cs *ring, * If there isn't a request associated with this submission, * create one as a temporary holder. */ - WARN(1, "execlist context submission without request"); request = kzalloc(sizeof(*request), GFP_KERNEL); if (request == NULL) return -ENOMEM; request->ring = ring; request->ctx = to; + kref_init(&request->ref); + request->uniq = dev_priv->request_uniq++; + i915_gem_context_reference(request->ctx); } else { + i915_gem_request_reference(request); WARN_ON(to != request->ctx); } request->tail = tail; - i915_gem_request_reference(request); - i915_gem_context_reference(request->ctx); intel_runtime_pm_get(dev_priv); @@ -731,7 +732,6 @@ void intel_execlists_retire_requests(struct intel_engine_cs *ring) if (ctx_obj && (ctx != ring->default_context)) intel_lr_context_unpin(ring, ctx); intel_runtime_pm_put(dev_priv); - i915_gem_context_unreference(ctx); list_del(&req->execlist_link); i915_gem_request_unreference(req); } -- 2.20.1