From: Rob Clark robdclark@chromium.org
commit afce71ff6daa9c0f852df0727fe32c6fb107f0fa upstream.
gem_context_register() makes the context visible to userspace, and which point a separate thread can trigger the I915_GEM_CONTEXT_DESTROY ioctl. So we need to ensure that nothing uses the ctx ptr after this. And we need to ensure that adding the ctx to the xarray is the *last* thing that gem_context_register() does with the ctx pointer.
Signed-off-by: Rob Clark robdclark@chromium.org Fixes: eb4dedae920a ("drm/i915/gem: Delay tracking the GEM context until it is registered") Fixes: a4c1cdd34e2c ("drm/i915/gem: Delay context creation (v3)") Fixes: 49bd54b390c2 ("drm/i915: Track all user contexts per client") Cc: stable@vger.kernel.org # v5.10+ Reviewed-by: Tvrtko Ursulin tvrtko.ursulin@intel.com Reviewed-by: Andi Shyti andi.shyti@linux.intel.com [tursulin: Stable and fixes tags add/tidy.] Signed-off-by: Tvrtko Ursulin tvrtko.ursulin@intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20230103234948.1218393-1-robdc... (cherry picked from commit bed4b455cf5374e68879be56971c1da563bcd90c) Signed-off-by: Rodrigo Vivi rodrigo.vivi@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/gpu/drm/i915/gem/i915_gem_context.c | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-)
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -1688,6 +1688,10 @@ void i915_gem_init__contexts(struct drm_ init_contexts(&i915->gem.contexts); }
+/* + * Note that this implicitly consumes the ctx reference, by placing + * the ctx in the context_xa. + */ static void gem_context_register(struct i915_gem_context *ctx, struct drm_i915_file_private *fpriv, u32 id) @@ -1703,10 +1707,6 @@ static void gem_context_register(struct snprintf(ctx->name, sizeof(ctx->name), "%s[%d]", current->comm, pid_nr(ctx->pid));
- /* And finally expose ourselves to userspace via the idr */ - old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); - WARN_ON(old); - spin_lock(&ctx->client->ctx_lock); list_add_tail_rcu(&ctx->client_link, &ctx->client->ctx_list); spin_unlock(&ctx->client->ctx_lock); @@ -1714,6 +1714,10 @@ static void gem_context_register(struct spin_lock(&i915->gem.contexts.lock); list_add_tail(&ctx->link, &i915->gem.contexts.list); spin_unlock(&i915->gem.contexts.lock); + + /* And finally expose ourselves to userspace via the idr */ + old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL); + WARN_ON(old); }
int i915_gem_context_open(struct drm_i915_private *i915, @@ -2199,14 +2203,22 @@ finalize_create_context_locked(struct dr if (IS_ERR(ctx)) return ctx;
+ /* + * One for the xarray and one for the caller. We need to grab + * the reference *prior* to making the ctx visble to userspace + * in gem_context_register(), as at any point after that + * userspace can try to race us with another thread destroying + * the context under our feet. + */ + i915_gem_context_get(ctx); + gem_context_register(ctx, file_priv, id);
old = xa_erase(&file_priv->proto_context_xa, id); GEM_BUG_ON(old != pc); proto_context_close(file_priv->dev_priv, pc);
- /* One for the xarray and one for the caller */ - return i915_gem_context_get(ctx); + return ctx; }
struct i915_gem_context *