From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 EF48B1917C7 for ; Fri, 18 Oct 2024 23:17:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729293451; cv=none; b=H0yGPci6BY9DuM0BR8gAcgz9tc6jv60xuz/Y1FMt5QIGobXI0JF1Ma2aXR67U+0FmN1WvarMDp6IVDggoJk2gzKyLxZMz9qxysqouSfXckeDsQC54t9n0fxwDC8b/HzKjOz2DTda1keyZNpfeqyzhKgtTBNrkWPF3IpGYg5cYVs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729293451; c=relaxed/simple; bh=k5T5wTYTqgSy7/I+hbZvHYXemGzjiQgMfT6xYzXLZck=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=D3PQLtCQXUHaC4w4regG/0Vrea5RO6P1cYTUMt8Jw618iI6IWIqsa5EzRMXv4aN9GrxN9yfN9igpt95i0w/gc5L/AcRN+4108QgU+55uFtXP6ZBTTzlXls+/s98GtJI0rj2dOSjzOgTpTW8Vfj5ScKtP72Glrbln6OWI8oUSCMM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none 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=YjOG37WX; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none 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="YjOG37WX" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1729293448; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=PgUruadhckuS2hgU+skGXtFOZJytmmA5aqcmbk2gB3o=; b=YjOG37WXNHj0bOzeDeaSRxqxs+WpmmUuMyNTP52khUigs2hQFmUNymMbMzsGpaCqsl2r3u dwoGyWbaUQjrza7085SY2agHJdDzj9uK9G7V24nz2ur+4jNX5o1lgWPbGv277CENMF9Htk hqJPDFINwEGGwMMaHNbCqzqXli+23kg= Received: from mx-prod-mc-04.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-614-mWtCu5YfMeGDzG6MbOtB7A-1; Fri, 18 Oct 2024 19:17:24 -0400 X-MC-Unique: mWtCu5YfMeGDzG6MbOtB7A-1 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (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-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 183FF19560A5; Fri, 18 Oct 2024 23:17:21 +0000 (UTC) Received: from chopper.redhat.com (unknown [10.22.65.88]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 537721956086; Fri, 18 Oct 2024 23:17:15 +0000 (UTC) From: Lyude Paul To: rust-for-linux@vger.kernel.org Cc: Danilo Krummrich , airlied@redhat.com, Ingo Molnar , Will Deacon , Waiman Long , Peter Zijlstra , Thomas Gleixner , linux-kernel@vger.kernel.org, Benno Lossin , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , Andreas Hindborg , Alice Ryhl , Trevor Gross , Martin Rodriguez Reboredo , Valentin Obst , Filipe Xavier , Fiona Behrens , Wedson Almeida Filho , Danilo Krummrich Subject: [PATCH v7 2/3] rust: sync: Introduce lock::Backend::Context and lock::BackendWithContext Date: Fri, 18 Oct 2024 19:13:51 -0400 Message-ID: <20241018231621.474601-4-lyude@redhat.com> In-Reply-To: <20241018231621.474601-2-lyude@redhat.com> References: <20241018231621.474601-2-lyude@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Now that we've introduced an `IrqDisabled` token for marking contexts in which IRQs are disabled, we need a way to be able to pass it to locks that require that IRQs are disabled. In order to continue using the `lock::Backend` type instead of inventing our own thing, we accomplish this by adding the associated Context type, along with a `lock_with()` function that can accept a Context when acquiring a lock. To allow current users of context-less locks to keep using the normal `lock()` method, we take an example from Wedson Almeida Filho's work and add a `where T<'a>: Default` bound to `lock()` so that it can only be called on lock types where the context is simply a placeholder value, then re-implement it through the new `lock_with()` function. We additionally add a BackendWithContext trait, to handle calling the various locking primatives necessary for these types - along with providing a `lock_with_new()` function for using those primitives and creating the relevant context tokens. Signed-off-by: Lyude Paul Suggested-by: Benno Lossin --- V3: * Use explicit lifetimes in lock_with() to ensure self and _context have the same lifetime (Benno) * Use () for locks that don't need a Context instead of PhantomData (Benno) V4: * Fix typo (Dirk) V7: * Introduce BackendWithContext and lock_with_new following tglx's feedback * Name functions lock_with_context_saved and unlock_with_context_restored Signed-off-by: Lyude Paul --- rust/kernel/sync/lock.rs | 118 ++++++++++++++++++++++++++++-- rust/kernel/sync/lock/mutex.rs | 1 + rust/kernel/sync/lock/spinlock.rs | 1 + 3 files changed, 115 insertions(+), 5 deletions(-) diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs index 7b4859b05d3a7..8949a69dd53c5 100644 --- a/rust/kernel/sync/lock.rs +++ b/rust/kernel/sync/lock.rs @@ -12,7 +12,7 @@ str::CStr, types::{NotThreadSafe, Opaque, ScopeGuard}, }; -use core::{cell::UnsafeCell, marker::PhantomPinned}; +use core::{cell::UnsafeCell, marker::PhantomPinned, mem::ManuallyDrop}; use macros::pin_data; pub mod mutex; @@ -43,6 +43,11 @@ pub unsafe trait Backend { /// [`unlock`]: Backend::unlock type GuardState; + /// The context which must be provided to acquire the lock. + /// + /// Can be `()`, or another type if [`BackendWithContext`] is implemented. + type Context<'a>; + /// Initialises the lock. /// /// # Safety @@ -89,6 +94,54 @@ unsafe fn relock(ptr: *mut Self::State, guard_state: &mut Self::GuardState) { } } +/// An additional trait for [`Backend`] implementations with a non-`()` [`Context`]. +/// +/// Restricts the context in which a [`Lock`] may be locked. It can initially be created using +/// [`Lock::lock_with_new`], and can be reused to acquire additional [`Lock`] objects using +/// [`Lock::lock_with`]. +/// +/// An example of a locking context would be a context in which local CPU interrupts are disabled, +/// where we must restrict the ability to acquire the [`Lock`] so that it can only be acquired +/// within that context. +/// +/// [`Context`]: `Backend::Context` +pub trait BackendWithContext: Backend { + /// The type that represents the state of this [`Context`]. + /// + /// [`Context`]: Backend::Context + type ContextState; + + /// Fulfills the invariants of [`State`] and acquires the lock, making the caller its owner. + /// + /// This returns any state data ([`Context::State`]) needed upon unlock. + /// + /// # Safety + /// + /// * Same as [`Backend::lock`]. + /// + /// [`State`]: Context::State + unsafe fn lock_with_context_saved<'a>( + ptr: *mut Self::State, + ) -> (Self::Context<'a>, Self::ContextState, Self::GuardState); + + /// Performs the final unlock within [`Context`]. + /// + /// Passes the [`Context::State`] returned from [`first_lock`]. + /// + /// # Safety + /// + /// * This function may only be called after [`first_lock`]. + /// * `state` must be the value returned from [`first_lock`]. + /// + /// [`first_lock`]: Backend::first_lock + /// [`Context`]: Backend::Context + unsafe fn unlock_with_context_restored( + ptr: *mut Self::State, + guard_state: &Self::GuardState, + context_state: Self::ContextState, + ); +} + /// A mutual exclusion primitive. /// /// Exposes one of the kernel locking primitives. Which one is exposed depends on the lock @@ -132,8 +185,9 @@ pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinIni } impl Lock { - /// Acquires the lock and gives the caller access to the data protected by it. - pub fn lock(&self) -> Guard<'_, T, B> { + /// Acquires the lock with the given context and gives the caller access to the data protected + /// by it. + pub fn lock_with<'a>(&'a self, _context: B::Context<'a>) -> Guard<'a, T, B> { // SAFETY: The constructor of the type calls `init`, so the existence of the object proves // that `init` was called. let state = unsafe { B::lock(self.state.get()) }; @@ -141,14 +195,68 @@ pub fn lock(&self) -> Guard<'_, T, B> { unsafe { Guard::new(self, state) } } - /// Tries to acquire the lock. + /// Acquires the lock and gives the caller access to the data protected by it. + #[inline] + pub fn lock<'a>(&'a self) -> Guard<'a, T, B> + where + B::Context<'a>: Default, + { + self.lock_with(Default::default()) + } + + /// Tries to acquire the lock with the given context. /// /// Returns a guard that can be used to access the data protected by the lock if successful. - pub fn try_lock(&self) -> Option> { + pub fn try_lock_with<'a>(&'a self, _context: B::Context<'a>) -> Option> { // SAFETY: The constructor of the type calls `init`, so the existence of the object proves // that `init` was called. unsafe { B::try_lock(self.state.get()).map(|state| Guard::new(self, state)) } } + + /// Tries to acquire the lock. + /// + /// Returns a guard that can be used to access the data protected by the lock if successful. + #[inline] + pub fn try_lock<'a>(&'a self) -> Option> + where + B::Context<'a>: Default, + { + self.try_lock_with(Default::default()) + } +} + +impl Lock { + /// Acquire the lock with a new [`Context`]. + /// + /// Creates a new instance of [`Context`], and then calls `cb` with said [`Context`] and a + /// [`Guard`] for `self`. The [`Context`] will be dropped once `cb` finishes, and it may be used + /// within `cb` to acquire additional locks. + /// + /// [`Context`]: Backend::Context + pub fn lock_with_new<'a, R>( + &self, + cb: impl FnOnce(&mut Guard<'_, T, B>, B::Context<'a>) -> R, + ) -> R { + let ptr = self.state.get(); + + // SAFETY: The constructor of the type calls `init`, so the existence of the object proves + // that `init` was called. + let (context, context_state, guard_state) = unsafe { B::lock_with_context_saved(ptr) }; + + // We don't want Guard's destructor to get called, since we'll drop the lock manually with + // B::unlock_with_context_restored later. So we store it in a ManuallyDrop and pass it to cb + // via reference. + // SAFETY: We acquired the lock when we called [`B::lock_with_context_saved`] above. + let mut guard = ManuallyDrop::new(unsafe { Guard::new(self, guard_state) }); + + let result = cb(&mut guard, context); + + // SAFETY: We called `B::lock_with_context_saved` above, `context_state` was returned from + // there. + unsafe { B::unlock_with_context_restored(ptr, &guard.state, context_state) }; + + result + } } /// A lock guard. diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs index 9ce43ccb45158..9a873cb5b438b 100644 --- a/rust/kernel/sync/lock/mutex.rs +++ b/rust/kernel/sync/lock/mutex.rs @@ -93,6 +93,7 @@ macro_rules! new_mutex { unsafe impl super::Backend for MutexBackend { type State = bindings::mutex; type GuardState = (); + type Context<'a> = (); unsafe fn init( ptr: *mut Self::State, diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs index 040dc16975a68..9fbfd96ffba3e 100644 --- a/rust/kernel/sync/lock/spinlock.rs +++ b/rust/kernel/sync/lock/spinlock.rs @@ -92,6 +92,7 @@ macro_rules! new_spinlock { unsafe impl super::Backend for SpinLockBackend { type State = bindings::spinlock_t; type GuardState = (); + type Context<'a> = (); unsafe fn init( ptr: *mut Self::State, -- 2.47.0