From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A8C45188CB1 for ; Thu, 11 Sep 2025 18:57:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757617079; cv=none; b=d9Fvjfe/HUUXCUedacIISNzNY44FTXjckA6yu53+HDwIKCwVOTE1oIeT6BfAKkNZ77HjhRDND9skBfn4YZtjhdShPwYxllCxfwYu5/8hqjOCHWjAlVHMW0tkEkwhc+MSF/yLtNFmizWklVoqbGOgpWI/j06nIMUJA4JRNhrmESs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757617079; c=relaxed/simple; bh=oeGFhXqo5ZBKpJuMsDxY9Z2BX4a2XSfCzho+kOY2tf0=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:Content-Type; b=ugICnpAl72OneUCYN8YAHUIgtlr8Y4jDri2rqECsdeqQg2l8hqEy1gT/E73nIWotee/AbpYn9H5UVJqFketJmJI9hMw88HNUR6JaqmvnXyK2u9m5IARI6elfwFNumxcbRZDATBBIJmIr01enk0W1V6kRTG3fv0/xwCiCaOgSuro= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=ScY81/GK; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ScY81/GK" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1757617076; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=0Thl7XTeKGfzx0k+KJGqjMASEd2oDUNwwwlWWZaVka4=; b=ScY81/GKdWRh5s5mKWy/wzKkEcFlg920Rz2KGvnbF91SK23UT3ddcZJzOoCROCx0W6LHyz Wx4zD1sZ7NglrXH6c44C4YcjZrF6O0PbcvEgu5BAWoJLlc/z9vuR6iSMGbkc5UHE0Jt8fB pBUsIUp9UAidFN4ZcZQ3Q26xeizctcA= Received: from mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-589-Me-ESYeZM1KFRFAsngsSDA-1; Thu, 11 Sep 2025 14:57:53 -0400 X-MC-Unique: Me-ESYeZM1KFRFAsngsSDA-1 X-Mimecast-MFC-AGG-ID: Me-ESYeZM1KFRFAsngsSDA_1757617070 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C22C519560BC; Thu, 11 Sep 2025 18:57:48 +0000 (UTC) Received: from chopper.redhat.com (unknown [10.22.65.223]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 0484719560BE; Thu, 11 Sep 2025 18:57:43 +0000 (UTC) From: Lyude Paul To: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Daniel Almeida , Shankari Anand , Asahi Lina Subject: [PATCH v2 1/2] Partially revert "rust: drm: gem: Implement AlwaysRefCounted for all gem objects automatically" Date: Thu, 11 Sep 2025 14:56:04 -0400 Message-ID: <20250911185739.511510-1-lyude@redhat.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Currently in order to implement AlwaysRefCounted for gem objects, we use a blanket implementation: unsafe impl AlwaysRefCounted for T { … } While this technically works, it comes with the rather unfortunate downside that attempting to create a similar blanket implementation in any other kernel crate will now fail in a rather confusing way. Using an example from the (not yet upstream) rust DRM KMS bindings, if we were to add: unsafe impl AlwaysRefCounted for T { … } Then the moment that both blanket implementations are present in the same kernel tree, compilation fails with the following: error[E0119]: conflicting implementations of trait `types::AlwaysRefCounted` --> rust/kernel/drm/kms.rs:504:1 | 504 | unsafe impl AlwaysRefCounted for T { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation | ::: rust/kernel/drm/gem/mod.rs:97:1 | 97 | unsafe impl AlwaysRefCounted for T { | ---------------------------------------------------- first implementation here So, revert these changes for now. The proper fix for this is to introduce a macro for copy/pasting the same implementation of AlwaysRefCounted around. This reverts commit 38cb08c3fcd3f3b1d0225dcec8ae50fab5751549. Signed-off-by: Lyude Paul --- V2: * Rewrite the commit message to explain a bit more why we don't want a blanket implementation for this. --- rust/kernel/drm/gem/mod.rs | 36 ++++++++++++++++-------------------- 1 file changed, 16 insertions(+), 20 deletions(-) diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs index 6ccbb25628a1e..daa92f0eac68e 100644 --- a/rust/kernel/drm/gem/mod.rs +++ b/rust/kernel/drm/gem/mod.rs @@ -55,26 +55,6 @@ pub trait IntoGEMObject: Sized + super::private::Sealed + AlwaysRefCounted { unsafe fn from_raw<'a>(self_ptr: *mut bindings::drm_gem_object) -> &'a Self; } -// SAFETY: All gem objects are refcounted. -unsafe impl AlwaysRefCounted for T { - fn inc_ref(&self) { - // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. - unsafe { bindings::drm_gem_object_get(self.as_raw()) }; - } - - unsafe fn dec_ref(obj: NonNull) { - // SAFETY: We either hold the only refcount on `obj`, or one of many - meaning that no one - // else could possibly hold a mutable reference to `obj` and thus this immutable reference - // is safe. - let obj = unsafe { obj.as_ref() }.as_raw(); - - // SAFETY: - // - The safety requirements guarantee that the refcount is non-zero. - // - We hold no references to `obj` now, making it safe for us to potentially deallocate it. - unsafe { bindings::drm_gem_object_put(obj) }; - } -} - extern "C" fn open_callback( raw_obj: *mut bindings::drm_gem_object, raw_file: *mut bindings::drm_file, @@ -273,6 +253,22 @@ extern "C" fn free_callback(obj: *mut bindings::drm_gem_object) { } } +// SAFETY: Instances of `Object` are always reference-counted. +unsafe impl crate::types::AlwaysRefCounted for Object { + fn inc_ref(&self) { + // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. + unsafe { bindings::drm_gem_object_get(self.as_raw()) }; + } + + unsafe fn dec_ref(obj: NonNull) { + // SAFETY: `obj` is a valid pointer to an `Object`. + let obj = unsafe { obj.as_ref() }; + + // SAFETY: The safety requirements guarantee that the refcount is non-zero. + unsafe { bindings::drm_gem_object_put(obj.as_raw()) } + } +} + impl super::private::Sealed for Object {} impl Deref for Object { base-commit: cf4fd52e323604ccfa8390917593e1fb965653ee -- 2.51.0