From c238980efd3b35af70fc926066cf7440f50a97a9 Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Thu, 2 Sep 2021 16:20:48 +0200 Subject: [PATCH] drm/i915: Release ctx->syncobj on final put, not on ctx close MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit gem context refcounting is another exercise in least locking design it seems, where most things get destroyed upon context closure (which can race with anything really). Only the actual memory allocation and the locks survive while holding a reference. This tripped up Jason when reimplementing the single timeline feature in commit 00dae4d3d35d4f526929633b76e00b0ab4d3970d Author: Jason Ekstrand Date: Thu Jul 8 10:48:12 2021 -0500 drm/i915: Implement SINGLE_TIMELINE with a syncobj (v4) We could fix the bug by holding ctx->mutex in execbuf and clear the pointer (again while holding the mutex) context_close, but it's cleaner to just make the context object actually invariant over its _entire_ lifetime. This way any other ioctl that's potentially racing, but holding a full reference, can still rely on ctx->syncobj being an immutable pointer. Which without this change, is not the case. Reviewed-by: Maarten Lankhorst Signed-off-by: Daniel Vetter Fixes: 00dae4d3d35d ("drm/i915: Implement SINGLE_TIMELINE with a syncobj (v4)") Cc: Jason Ekstrand Cc: Chris Wilson Cc: Tvrtko Ursulin Cc: Joonas Lahtinen Cc: Matthew Brost Cc: Matthew Auld Cc: Maarten Lankhorst Cc: "Thomas Hellström" Cc: Lionel Landwerlin Cc: Dave Airlie Link: https://patchwork.freedesktop.org/patch/msgid/20210902142057.929669-2-daniel.vetter@ffwll.ch --- drivers/gpu/drm/i915/gem/i915_gem_context.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c index 051bc357ff650..5a053cf149482 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -994,6 +994,9 @@ static void i915_gem_context_release_work(struct work_struct *work) trace_i915_context_free(ctx); GEM_BUG_ON(!i915_gem_context_is_closed(ctx)); + if (ctx->syncobj) + drm_syncobj_put(ctx->syncobj); + mutex_destroy(&ctx->engines_mutex); mutex_destroy(&ctx->lut_mutex); @@ -1220,9 +1223,6 @@ static void context_close(struct i915_gem_context *ctx) if (vm) i915_vm_close(vm); - if (ctx->syncobj) - drm_syncobj_put(ctx->syncobj); - ctx->file_priv = ERR_PTR(-EBADF); /* -- 2.39.5