From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0CB20C44521 for ; Sat, 18 Jul 2026 05:33:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DB2906B0145; Sat, 18 Jul 2026 01:33:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D3BF06B0147; Sat, 18 Jul 2026 01:33:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B8F1E6B0148; Sat, 18 Jul 2026 01:33:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 726966B0145 for ; Sat, 18 Jul 2026 01:33:09 -0400 (EDT) Received: from smtpin02.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id C85E5401F0 for ; Sat, 18 Jul 2026 05:33:08 +0000 (UTC) X-FDA: 85000778856.02.FCEC7E6 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf25.hostedemail.com (Postfix) with ESMTP id D2777A0007 for ; Sat, 18 Jul 2026 05:33:06 +0000 (UTC) Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=MwbqhS59; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf25.hostedemail.com: domain of boqun@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=boqun@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1784352786; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=agZo2XMu3L0K2ubakxGylN/JFYjmY5Vh7gaRmN8isS0=; b=YDUl7AiMx2xAzY2FC7om+A8wsdf4HrIK38jbKv0fTMZfGcvYa1TPRiGRr4RF+2K4cJ0WK0 Cx29m1fYJ9GFptEeHNIJ/s+cHSpDNlHGoi9shCnzzuA4w/9Uqtd95saxKHyo9FWgFlVT7G crUgBSqHz3wsimcfdIHcVt2oW/JXSpU= ARC-Authentication-Results: i=1; imf25.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=MwbqhS59; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf25.hostedemail.com: domain of boqun@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=boqun@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1784352786; b=52FofO3H4+TMudqkQpPibDZS92e6t1qcJBysKtUFI9Ci/U08q44h8DJdVhjKASbqgxha8z UbBhH5vQY9vSO/47MRw6QwwNh7D10nQfk9Q9qwQMef47U5wQ2pMwZjOKO3OMiZk40+5atZ 7KaBslysMowI60SlpDNDdRgkaaONb74= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 76F0560AB5; Sat, 18 Jul 2026 05:33:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1CF771F00A3D; Sat, 18 Jul 2026 05:33:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784352786; bh=agZo2XMu3L0K2ubakxGylN/JFYjmY5Vh7gaRmN8isS0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=MwbqhS59pHFX2y1bjCbULv/pCDqqg/3CNZTpDqkOxuqIBllpv6JuP2ceX0z4ojwaC hFcGSdyF26rxMWJerVgJwtbmAMxEaiNAZRCba8S6mwOIsS1xmVj0mRmaV9xuhV2YMi BVgHXSxVwuvhrdOqZ1zuvlp+lIhZbP8Et1IjKpLehemcIMVQm5B82uXKWjO/8IdEhs +MsHZn4wxWxhILUdNXdR8MeVp5F4MHKZjegrurQn2HatPRi4P1YswdCYvni7/ombXc sVC1628sS6njMIV6WsvNjc2olUvHZlDljdFAlSQj63c1HcaWsn4q3UExFh6mwES36f sYOXLcAJwL4BQ== Received: from phl-compute-04.internal (phl-compute-04.internal [10.202.2.44]) by mailfauth.phl.internal (Postfix) with ESMTP id 4D860F40067; Sat, 18 Jul 2026 01:33:04 -0400 (EDT) Received: from phl-frontend-03 ([10.202.2.162]) by phl-compute-04.internal (MEProxy); Sat, 18 Jul 2026 01:33:04 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: dmFkZTEgEAJxx43zj+N2HexbcXxXpr8iZewHIC+wBoUe/3kHvIsxmf0uovnwyzmQf22fh5 PbBpjLE4M1x+gkTl4x5OuQgzkddFgVOLc7SPm8OVC3wj6PmDWqpG/wyzm0HbMF//9RDtvM cqERhXH8fRAethPTEdiPCDM2biIjvo2duSrcDNiRwIZ4PJTMN9f05eRQvmRRsxcI1+ZGXR GIOp0pU8kR4mYsSetTdmMF1Q09Qod6lgNc4Vx07svlwAfyl7KUdd5xFGJoXDRG1kaoRL4T /VNW+87mn/mN1dMvhE363j1dLxUYIFMMuhRaBTcK4fjHHNruAjFs082R/vn5pb6pwik6oO i02M8fONfup6UUyVvWAj3LIiaccJx79xi00AFE7MEV3WF030lZ8xA8SpsEi6Gl4rTphLm7 W85qiFkiPnFPEyGQsPlpzBH5SC88pTqTl7zHOgB1UizF1X8HWy0pjCGlfqlb5KhMIGeksB BM77F8Iz5gz4nm5AaBX89I/O5EsTxlSPFMjiVPNKun4nrYJZwlRKq2rf9JutxjHhCePeF2 ZUczb4x89X5B2J5KgEEM0Ar+g8NYdZYNAfHEmuK+asohxaGqvLq7z5ddhcnnsaaXdjRYl3 r6LYJ4YMNhLSLVbKF0j9W9SxoIz0cRSZGuTCLSTBHjntmeBEzvh958UnZESQ X-ME-Proxy: Feedback-ID: i8dbe485b:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Sat, 18 Jul 2026 01:33:03 -0400 (EDT) From: Boqun Feng To: rust-for-linux@vger.kernel.org, rcu@vger.kernel.org Cc: Miguel Ojeda , Boqun Feng , Gary Guo , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Daniel Almeida , Tamir Duberstein , Alexandre Courbot , =?UTF-8?q?Onur=20=C3=96zkan?= , "Liam R. Howlett" , Andrew Ballance , Alexander Viro , Christian Brauner , Jan Kara , Lyude Paul , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Sumit Semwal , =?UTF-8?q?Christian=20K=C3=B6nig?= , Greg Kroah-Hartman , "Yury Norov (NVIDIA)" , Asahi Lina , Matthew Maurer , Lorenzo Stoakes , linux-kernel@vger.kernel.org, maple-tree@lists.infradead.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org Subject: [NOT FOR MERGE] [RFC PATCH v2 4/4] rust: poll: use kfree_rcu() for PollCondVar Date: Fri, 17 Jul 2026 22:32:47 -0700 Message-ID: <20260718053247.25154-5-boqun@kernel.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260718053247.25154-1-boqun@kernel.org> References: <20260718053247.25154-1-boqun@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D2777A0007 X-Stat-Signature: on1fwjsrxynmiodin7swouenubhus7bf X-Rspam-User: X-HE-Tag: 1784352786-351748 X-HE-Meta: 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 AkRVVGqJ Op2IsrSM7EbeAlKpDy4ZL4Pu/VUQHrrBx331lcEc170dQMKbnWj08iPw4OJd0kAX8esQ+Q/qPk33nXffdt/AEebQ1xzk6N6Q2FbwcFrBmd4GTuzm4qCFZBq/uEyDyoFQcEfo15MecTE2fqzQ+uWEk3P/fL7SwsCyiiN59DlL3FQDxeLsev+T5W/d9785S8yFZjiHckWddKtD/esF7QO3wYGxJGrjr6Lz0UuS01maNk0BqvyRJQ9GeoRRLyUI78jnM1mosYrrGnKSQkLBKIxbN+WtCYJxlpfA9yIcCj1Whq02Q3RLJBBfto2kzIZMCAG3GQf+2Zk+gq23TbCazJADKgjFll0fkYWOC5mOr7BMLY07R+zQKYnJqG6faUjFVOgoeNlICSs1dsAvqPYY/A/lHBLAqNrWeJG9+kpYGcZBGSJIyzBhzEEtKhiUCY3uJA+umEuUc Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Alice Ryhl Rust Binder currently uses PollCondVar, but it calls synchronize_rcu() in the destructor, which we would like to avoid. Add a variation of PollCondVar that kfree_rcu() instead. One could avoid the `rcu` field and allocate the rcu_head on drop using a fallback to synchronize_rcu() on ENOMEM. However, I'd prefer to avoid the potential for synchronize_rcu(), and Binder will only use this for a small fraction of processes, so even if it changes which kmalloc bucket it falls into, the extra memory is not a problem. Signed-off-by: Alice Ryhl [boqun: Use RcuFreeSafe] Signed-off-by: Boqun Feng --- rust/kernel/sync/poll.rs | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-) diff --git a/rust/kernel/sync/poll.rs b/rust/kernel/sync/poll.rs index 5aa0ce9ba01b..830a4763a5c1 100644 --- a/rust/kernel/sync/poll.rs +++ b/rust/kernel/sync/poll.rs @@ -9,12 +9,19 @@ fs::File, prelude::*, sync::{ - rcu::synchronize_rcu, + rcu::{ + synchronize_rcu, // + RcuFreeSafe, + }, CondVar, LockClassKey, // }, // }; -use core::{marker::PhantomData, ops::Deref}; + +use core::{ + marker::PhantomData, + ops::Deref, // +}; /// Creates a [`PollCondVar`] initialiser with the given name and a newly-created lock class. #[macro_export] @@ -70,6 +77,7 @@ pub fn register_wait(&self, file: &File, cv: &PollCondVar) { /// /// [`CondVar`]: crate::sync::CondVar #[pin_data(PinnedDrop)] +#[repr(transparent)] pub struct PollCondVar { #[pin] inner: CondVar, @@ -97,12 +105,20 @@ fn deref(&self) -> &CondVar { impl PinnedDrop for PollCondVar { #[inline] fn drop(self: Pin<&mut Self>) { + self.drop_before_gp(); + + // Wait for epoll items to be properly removed. + synchronize_rcu(); + } +} + +// SAFETY: __wake_up_pollfree() guarantees all the epoll items on the wait list will be gone after +// one grace period. +unsafe impl RcuFreeSafe for PollCondVar { + fn drop_before_gp(self: Pin<&mut Self>) { // Clear anything registered using `register_wait`. // // SAFETY: The pointer points at a valid `wait_queue_head`. unsafe { bindings::__wake_up_pollfree(self.inner.wait_queue_head.get()) }; - - // Wait for epoll items to be properly removed. - synchronize_rcu(); } } -- 2.50.1 (Apple Git-155)