From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 DDFE7279DC2 for ; Fri, 31 Jul 2026 00:40:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785458423; cv=none; b=E0xNI4S8ZkgimC8IG8epy7azfRctKOUJDrdNhZ2yJr0c+DJ3FnpJJzTLCdvETO4L2AxV1uL1g5aWs2x6hAX16BT++aI+Yw4HHasg9dFZB2k6/PGclVuzrYKpElyRH1KUktjQCw3I167RDn8NgwWZRwa8+2a6MFD/hefFsFxxS1U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785458423; c=relaxed/simple; bh=JP4HsPVprQkHpETQ5y/3x8uTjNmAcZbMhQhkJSVfc78=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=h7FMBJJEMbN54bNNXI3mUxr13ArVxaHIrVFS0RV6wBiWyKQyKfBdcxLiU0U5RZKMUjhvuNUxCct9sF7tY+mJELnMMMqdtS6RNlJzq8QtY7FxFhXVsE6yOLOl4QIIX3AXCr6OzS683WRs3Ugul5d5WrqeeJ2MSPKBhBTo1Kw7coY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eL/FPHi2; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="eL/FPHi2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 995801F00ADB; Fri, 31 Jul 2026 00:40:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785458421; bh=8wsTnqSTiC+swf3nbDP8SAUQ5ZVb5/imjr4XGNyDQFU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=eL/FPHi2IH3fwhT3+zsiUKOZh+rqyINtWJodZhllBDAEki0eB+lDldoO1UAOVapRC PXOzHRDO9d5LyqlRfpL1FdsbdDnNWqvRZdWCAt8uGaUjpyiKt8aBJRbZEWTa+eSBgr ngzXFT3e/XjQ+pruGXcNjxtv9/5+z0lsU0n14aCCY6C3COFFduQr7ZFkcRyWxdYKnJ +6tutnlwfC/jrhqtWDOUwH6TDZXFE5/beTlyOPCikij9pjIqdXMkbsHJWIWzM3LpYG JnpMOVLgDlhH6b9atuGw0C/PyqqVCKYfyGNSB9ejCQ4F32C1/r2udDQ7+IpCgjO/Vv SK/N7CjxODt5g== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 410F7CE100D; Thu, 30 Jul 2026 17:40:21 -0700 (PDT) From: "Paul E. McKenney" To: Anna-Maria Behnsen , Frederic Weisbecker , Thomas Gleixner Cc: "Peter Zijlstra (Intel)" , linux-kernel@vger.kernel.org, kernel-team@meta.com, "Paul E. McKenney" , Ingo Molnar , Darren Hart , Davidlohr Bueso , =?UTF-8?q?Andr=C3=A9=20Almeida?= Subject: [PATCH RFC 5/9] futex: Use accessor for hrtimer_sleeper ->task field in waitwake.c Date: Thu, 30 Jul 2026 17:40:15 -0700 Message-Id: <20260731004019.3530210-5-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The hrtimer_sleeper structure's ->task field is used as a flag to indicate that the associated hrtimer has expired. This means that the hrtimer handler can be storing to this field while other code is loading from it to check for expiry. Note that additional races appear for hrtimers that can be restarted, which could be argued to be a user error. However, that is no reason to let the compiler introduce additional confusion, and to this end, the hrtimer_sleeper_task_get() was introduced, use of which also has the benefit of avoiding open-code access to hrtimer_sleeper innards. Therefore, apply this accessor to kernel/futex/waitwake.c. KCSAN located this issue. Signed-off-by: Paul E. McKenney Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Darren Hart Cc: Davidlohr Bueso Cc: "André Almeida" Cc: Anna-Maria Behnsen Cc: Frederic Weisbecker Cc: Thomas Gleixner --- kernel/futex/waitwake.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c index d4483d15d30a5d..cf18309e577030 100644 --- a/kernel/futex/waitwake.c +++ b/kernel/futex/waitwake.c @@ -383,7 +383,7 @@ void futex_do_wait(struct futex_q *q, struct hrtimer_sleeper *timeout) * flagged for rescheduling. Only call schedule if there * is no timeout, or if it has yet to expire. */ - if (!timeout || timeout->task) + if (!timeout || hrtimer_sleeper_task_get(timeout)) schedule(); } __set_current_state(TASK_RUNNING); @@ -539,7 +539,7 @@ int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *woken) static void futex_sleep_multiple(struct futex_vector *vs, unsigned int count, struct hrtimer_sleeper *to) { - if (to && !to->task) + if (to && !hrtimer_sleeper_task_get(to)) return; for (; count; count--, vs++) { @@ -590,7 +590,7 @@ int futex_wait_multiple(struct futex_vector *vs, unsigned int count, if (ret >= 0) return ret; - if (to && !to->task) + if (to && !hrtimer_sleeper_task_get(to)) return -ETIMEDOUT; else if (signal_pending(current)) return -ERESTARTSYS; @@ -725,7 +725,7 @@ int __futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, if (!futex_unqueue(&q)) return 0; - if (to && !to->task) + if (to && !hrtimer_sleeper_task_get(to)) return -ETIMEDOUT; /* -- 2.40.1