From nobody Thu Oct 2 03:14:57 2025 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 776E52820C7 for ; Wed, 24 Sep 2025 08:03:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758701021; cv=none; b=mc6XZX6psAWjSG0itvWtIWj0DkSNBe3HD2NR5IcUmmfnq9hAEsSqDNObfmA1wEpbIYd4MCDs65qRYQU0OsMLyCzL/1OaHfkbQQxolO96xVKV3ZPGSqKkShsft5TyZKlBJA/nt3BBoFEV7YgeZcE3ifTPjOV2vOy3kFpovNptWok= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758701021; c=relaxed/simple; bh=62ustbkopVhBdcLoC7hwC9z9bDpnZ7IWCPTGeIvCKP4=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=tCDITKBGRTPimll1G4iezmdl6qRWdnh+5irwwNOlUvfS+U7KRrJAaut6o8hrl3m5o3KLutadc/GVXwEpYNU1EKHd8zPbtflyE3Pz/3iKpPguH9NRLaZZHGWATEhxbMZ/hIqVq6Ou2XSr/TTxsIbkAv1v7jiPdcf1GXbnyn4Lm8I= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=K0g9fXm+; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="K0g9fXm+" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=Ua0dxI0J08PM8zvyZk5eD4nV7fTxFbZ9tXP0wSe2am4=; b=K0g9fXm+B6oxbUqjmInTle4xCS 0g2H7OEfBblBht8ZaLNwDTF5CwJZ9lCes3KvN4LipdYHTqs0swtcl3oHfKB2TOFERkRHtu67VnHpm tzozFMcYkjn/b2nS96AM188ggak4t+eVrO3akJB5q2Ku6Nz5SX17pPnS+zLys3DZfha0oECRO5bu6 0F72BuvN1kx6XoyJO/oWx799a2cM1N4ODlXsoLtbIhLj5wZDe2dKgQe3xg5MAei6cYFbhFZh/kutb C9+uhen+crC4GxOsrQq7IiTFJBZFoWW9ALMM7kApr18pBI8o3id2tlNEzYBwfLzO1FHUWFuywzgO4 mgtE0JzQ==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1v1KTO-0000000BeCi-00JQ; Wed, 24 Sep 2025 08:03:34 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 0) id 0117A30050D; Wed, 24 Sep 2025 10:03:32 +0200 (CEST) Message-ID: <20250924080118.425949403@infradead.org> User-Agent: quilt/0.68 Date: Wed, 24 Sep 2025 09:59:49 +0200 From: Peter Zijlstra To: jpoimboe@kernel.org, rostedt@kernel.org Cc: linux-kernel@vger.kernel.org, peterz@infradead.org Subject: [PATCH 01/12] task_work: Fix NMI race condition References: <20250924075948.579302904@infradead.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" __schedule() // disable irqs task_work_add(current, work, TWA_NMI_CURRENT); // current =3D next; // enable irqs task_work_set_notify_irq() test_and_set_tsk_thread_flag(current, TIF_NOTIFY_RESUME); // wrong task! // original task skips task work on its next return to user (or exit!) Fixes: 466e4d801cd4 ("task_work: Add TWA_NMI_CURRENT as an additional notif= y mode.") Reported-by: Josh Poimboeuf Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Steven Rostedt (Google) --- kernel/task_work.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -9,7 +9,12 @@ static struct callback_head work_exited; #ifdef CONFIG_IRQ_WORK static void task_work_set_notify_irq(struct irq_work *entry) { - test_and_set_tsk_thread_flag(current, TIF_NOTIFY_RESUME); + /* + * no-op IPI + * + * TWA_NMI_CURRENT will already have set the TIF flag, all + * this interrupt does it tickle the return-to-user path. + */ } static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) =3D IRQ_WORK_INIT_HARD(task_work_set_notify_irq); @@ -86,6 +91,7 @@ int task_work_add(struct task_struct *ta break; #ifdef CONFIG_IRQ_WORK case TWA_NMI_CURRENT: + set_tsk_thread_flag(current, TIF_NOTIFY_RESUME); irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume)); break; #endif