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 CC48A1662E7; Tue, 26 Aug 2025 14:16:06 +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=1756217766; cv=none; b=o7J0oNjpdhmk39aWvu6ngIgNGJmNMaEGRpAuCFJALm0ghNdGhlfpxF9uXDZonHr/jU+mNiN5NknCNHOV2nHDS25dn+BsbSG7YwPj6/OaBq9/xvgzxalsNQOwUAnotKiNhI61uQZQu4k0b98zC18boJ+cPM7Sny26FXNGhVSpUwQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756217766; c=relaxed/simple; bh=qWg82UlW2nXIdjK38SgAD2nHaH20QgwU3Cpoxepgx/k=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RlK0B0py4V8Qnhy2wyaXqOaUP9EdT78VDa/SFhDPyPUEgAkzHNSgms8eR2IOJ7v3XbkHiQ43OqhQrO0i//ADCrL6hYV0gcSb34sMUDeaHEv7TYHs+ZsNY0XuoPwgx3eGZeILyPF/QEP1ycH6aR+26LREBZnnCOyQFP8KxnbXHdM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=jKgzIV8t; 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="jKgzIV8t" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 29737C4CEF1; Tue, 26 Aug 2025 14:16:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1756217766; bh=qWg82UlW2nXIdjK38SgAD2nHaH20QgwU3Cpoxepgx/k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jKgzIV8tAdV5oMTXptsfB26inqUB+xrNSNxSBQYdlH1DQdfBja+rtKFrY6twe0+l/ /JiQp3tc8e5olsPqShRJrKulr5OjAZUMp/gAkFBfmJOOLQ9p3hKdMEip3ehNo2MeeK 2DKPOlgxnIQaxBuYjzF0DAvwWKRKp/ujQm2xbYh4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Paul E. McKenney" , Frederic Weisbecker , "Neeraj Upadhyay (AMD)" , Sasha Levin Subject: [PATCH 5.10 265/523] rcu: Protect ->defer_qs_iw_pending from data race Date: Tue, 26 Aug 2025 13:07:55 +0200 Message-ID: <20250826110930.963877237@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250826110924.562212281@linuxfoundation.org> References: <20250826110924.562212281@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paul E. McKenney [ Upstream commit 90c09d57caeca94e6f3f87c49e96a91edd40cbfd ] On kernels built with CONFIG_IRQ_WORK=y, when rcu_read_unlock() is invoked within an interrupts-disabled region of code [1], it will invoke rcu_read_unlock_special(), which uses an irq-work handler to force the system to notice when the RCU read-side critical section actually ends. That end won't happen until interrupts are enabled at the soonest. In some kernels, such as those booted with rcutree.use_softirq=y, the irq-work handler is used unconditionally. The per-CPU rcu_data structure's ->defer_qs_iw_pending field is updated by the irq-work handler and is both read and updated by rcu_read_unlock_special(). This resulted in the following KCSAN splat: ------------------------------------------------------------------------ BUG: KCSAN: data-race in rcu_preempt_deferred_qs_handler / rcu_read_unlock_special read to 0xffff96b95f42d8d8 of 1 bytes by task 90 on cpu 8: rcu_read_unlock_special+0x175/0x260 __rcu_read_unlock+0x92/0xa0 rt_spin_unlock+0x9b/0xc0 __local_bh_enable+0x10d/0x170 __local_bh_enable_ip+0xfb/0x150 rcu_do_batch+0x595/0xc40 rcu_cpu_kthread+0x4e9/0x830 smpboot_thread_fn+0x24d/0x3b0 kthread+0x3bd/0x410 ret_from_fork+0x35/0x40 ret_from_fork_asm+0x1a/0x30 write to 0xffff96b95f42d8d8 of 1 bytes by task 88 on cpu 8: rcu_preempt_deferred_qs_handler+0x1e/0x30 irq_work_single+0xaf/0x160 run_irq_workd+0x91/0xc0 smpboot_thread_fn+0x24d/0x3b0 kthread+0x3bd/0x410 ret_from_fork+0x35/0x40 ret_from_fork_asm+0x1a/0x30 no locks held by irq_work/8/88. irq event stamp: 200272 hardirqs last enabled at (200272): [] finish_task_switch+0x131/0x320 hardirqs last disabled at (200271): [] __schedule+0x129/0xd70 softirqs last enabled at (0): [] copy_process+0x4df/0x1cc0 softirqs last disabled at (0): [<0000000000000000>] 0x0 ------------------------------------------------------------------------ The problem is that irq-work handlers run with interrupts enabled, which means that rcu_preempt_deferred_qs_handler() could be interrupted, and that interrupt handler might contain an RCU read-side critical section, which might invoke rcu_read_unlock_special(). In the strict KCSAN mode of operation used by RCU, this constitutes a data race on the ->defer_qs_iw_pending field. This commit therefore disables interrupts across the portion of the rcu_preempt_deferred_qs_handler() that updates the ->defer_qs_iw_pending field. This suffices because this handler is not a fast path. Signed-off-by: Paul E. McKenney Reviewed-by: Frederic Weisbecker Signed-off-by: Neeraj Upadhyay (AMD) Signed-off-by: Sasha Levin --- kernel/rcu/tree_plugin.h | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index c07a84197173..ed17deba8b18 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -585,10 +585,13 @@ static void rcu_preempt_deferred_qs(struct task_struct *t) */ static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp) { + unsigned long flags; struct rcu_data *rdp; rdp = container_of(iwp, struct rcu_data, defer_qs_iw); + local_irq_save(flags); rdp->defer_qs_iw_pending = false; + local_irq_restore(flags); } /* -- 2.39.5