From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 57CFF1E511 for ; Mon, 16 Mar 2026 14:34:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773671654; cv=none; b=YfRI3BzkHIUL5v+tosM2VEUP+6ANfnoLaGRBG4aVmYTlUoOyqDHWrmxzKmCWBBwGpZtS1l/D0HO3DvZmqzG4LB+iiNHTyCLTo7Ulv0CHjMlZlCHBqGbxhhVx8opcAvkaP++4hNeAeNcuSbRZLa+pWFWo7XbgRXcXl4BOf4qJP8c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773671654; c=relaxed/simple; bh=yzVkz8h+UeYqUbXYKpLhjo4Omqel5Wb/hAojfc1PcOg=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=sEYJXqsZ/eZlmKpES+2xxMt0hjIcIw/5/G9061lVmjdRHv5AO0y0QAchISzV9hTRkDVAGO9kPSxB1CAonXw5tOkhsZjLCqH3/0S2oE9F7B43CZQ55oKmbHwh5/l/uEhKCqRvnK7oAoG/comDZjeXdB6gBaNR3McwB6p+zW7zK1g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=FOOZA33k; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="FOOZA33k" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 81449C19421; Mon, 16 Mar 2026 14:34:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1773671654; bh=yzVkz8h+UeYqUbXYKpLhjo4Omqel5Wb/hAojfc1PcOg=; h=Subject:To:Cc:From:Date:From; b=FOOZA33kAT5RPyePsDW1uFvKtewooPJr+0zYkauVZlZ6YcCoAPzAFw3Bd7sMUBFDU gN3MElIV+e3w8uvWbwcdLiDmqBHXMwqPhVDpWrUPhtGpc+cfOFAnh3WSh4JFAQSr/P kt7PIEdUQsm4Fh1jhAYf43f4Gic1+pxfyxfex4V4= Subject: FAILED: patch "[PATCH] rust: pin-init: replace shadowed return token by" failed to apply to 6.18-stable tree To: lossin@kernel.org,aliceryhl@google.com,gary@garyguo.net,ojeda@kernel.org,theemathas@gmail.com Cc: From: Date: Mon, 16 Mar 2026 15:34:02 +0100 Message-ID: <2026031602-badly-slackness-b379@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.18-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y git checkout FETCH_HEAD git cherry-pick -x fdbaa9d2b78e0da9e1aeb303bbdc3adfe6d8e749 # git commit -s git send-email --to '' --in-reply-to '2026031602-badly-slackness-b379@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From fdbaa9d2b78e0da9e1aeb303bbdc3adfe6d8e749 Mon Sep 17 00:00:00 2001 From: Benno Lossin Date: Wed, 11 Mar 2026 11:50:49 +0100 Subject: [PATCH] rust: pin-init: replace shadowed return token by `unsafe`-to-create token We use a unit struct `__InitOk` in the closure generated by the initializer macros as the return value. We shadow it by creating a struct with the same name again inside of the closure, preventing early returns of `Ok` in the initializer (before all fields have been initialized). In the face of Type Alias Impl Trait (TAIT) and the next trait solver, this solution no longer works [1]. The shadowed struct can be named through type inference. In addition, there is an RFC proposing to add the feature of path inference to Rust, which would similarly allow [2]. Thus remove the shadowed token and replace it with an `unsafe` to create token. The reason we initially used the shadowing solution was because an alternative solution used a builder pattern. Gary writes [3]: In the early builder-pattern based InitOk, having a single InitOk type for token is unsound because one can launder an InitOk token used for one place to another initializer. I used a branded lifetime solution, and then you figured out that using a shadowed type would work better because nobody could construct it at all. The laundering issue does not apply to the approach we ended up with today. With this change, the example by Tim Chirananthavat in [1] no longer compiles and results in this error: error: cannot construct `pin_init::__internal::InitOk` with struct literal syntax due to private fields --> src/main.rs:26:17 | 26 | InferredType {} | ^^^^^^^^^^^^ | = note: private field `0` that was not provided help: you might have meant to use the `new` associated function | 26 - InferredType {} 26 + InferredType::new() | Applying the suggestion of using the `::new()` function, results in another expected error: error[E0133]: call to unsafe function `pin_init::__internal::InitOk::new` is unsafe and requires unsafe block --> src/main.rs:26:17 | 26 | InferredType::new() | ^^^^^^^^^^^^^^^^^^^ call to unsafe function | = note: consult the function's documentation for information on how to avoid undefined behavior Reported-by: Tim Chirananthavat Link: https://github.com/rust-lang/rust/issues/153535 [1] Link: https://github.com/rust-lang/rfcs/pull/3444#issuecomment-4016145373 [2] Link: https://github.com/rust-lang/rust/issues/153535#issuecomment-4017620804 [3] Fixes: fc6c6baa1f40 ("rust: init: add initialization macros") Cc: stable@vger.kernel.org Signed-off-by: Benno Lossin Reviewed-by: Alice Ryhl Reviewed-by: Gary Guo Link: https://patch.msgid.link/20260311105056.1425041-1-lossin@kernel.org [ Added period as mentioned. - Miguel ] Signed-off-by: Miguel Ojeda diff --git a/rust/pin-init/internal/src/init.rs b/rust/pin-init/internal/src/init.rs index 738f62c8105c..2fe918f4d82a 100644 --- a/rust/pin-init/internal/src/init.rs +++ b/rust/pin-init/internal/src/init.rs @@ -148,11 +148,6 @@ fn assert_zeroable(_: *mut T) let init_fields = init_fields(&fields, pinned, &data, &slot); let field_check = make_field_check(&fields, init_kind, &path); Ok(quote! {{ - // We do not want to allow arbitrary returns, so we declare this type as the `Ok` return - // type and shadow it later when we insert the arbitrary user code. That way there will be - // no possibility of returning without `unsafe`. - struct __InitOk; - // Get the data about fields from the supplied type. // SAFETY: TODO let #data = unsafe { @@ -162,18 +157,15 @@ fn assert_zeroable(_: *mut T) #path::#get_data() }; // Ensure that `#data` really is of type `#data` and help with type inference: - let init = ::pin_init::__internal::#data_trait::make_closure::<_, __InitOk, #error>( + let init = ::pin_init::__internal::#data_trait::make_closure::<_, #error>( #data, move |slot| { - { - // Shadow the structure so it cannot be used to return early. - struct __InitOk; - #zeroable_check - #this - #init_fields - #field_check - } - Ok(__InitOk) + #zeroable_check + #this + #init_fields + #field_check + // SAFETY: we are the `init!` macro that is allowed to call this. + Ok(unsafe { ::pin_init::__internal::InitOk::new() }) } ); let init = move |slot| -> ::core::result::Result<(), #error> { diff --git a/rust/pin-init/src/__internal.rs b/rust/pin-init/src/__internal.rs index 90f18e9a2912..90adbdc1893b 100644 --- a/rust/pin-init/src/__internal.rs +++ b/rust/pin-init/src/__internal.rs @@ -46,6 +46,24 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> { } } +/// Token type to signify successful initialization. +/// +/// Can only be constructed via the unsafe [`Self::new`] function. The initializer macros use this +/// token type to prevent returning `Ok` from an initializer without initializing all fields. +pub struct InitOk(()); + +impl InitOk { + /// Creates a new token. + /// + /// # Safety + /// + /// This function may only be called from the `init!` macro in `../internal/src/init.rs`. + #[inline(always)] + pub unsafe fn new() -> Self { + Self(()) + } +} + /// This trait is only implemented via the `#[pin_data]` proc-macro. It is used to facilitate /// the pin projections within the initializers. /// @@ -68,9 +86,10 @@ pub unsafe trait PinData: Copy { type Datee: ?Sized + HasPinData; /// Type inference helper function. - fn make_closure(self, f: F) -> F + #[inline(always)] + fn make_closure(self, f: F) -> F where - F: FnOnce(*mut Self::Datee) -> Result, + F: FnOnce(*mut Self::Datee) -> Result, { f } @@ -98,9 +117,10 @@ pub unsafe trait InitData: Copy { type Datee: ?Sized + HasInitData; /// Type inference helper function. - fn make_closure(self, f: F) -> F + #[inline(always)] + fn make_closure(self, f: F) -> F where - F: FnOnce(*mut Self::Datee) -> Result, + F: FnOnce(*mut Self::Datee) -> Result, { f }