From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail115-171.sinamail.sina.com.cn (mail115-171.sinamail.sina.com.cn [218.30.115.171]) (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 36E53190490 for ; Wed, 5 Jun 2024 11:11:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=218.30.115.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717585916; cv=none; b=QLzwsnVHlvuQ3hhKWZHpLCJjtfhraUjELO0VqBbxFk+9Cnb1q7QipMR2WS6uho8LCQi42Cavb8ejDbkOOvU09J0c5rM4USQ1vnfBXINCuSEalqC8s41fRPXw5xRCBWuFUNjYH9zHUIu0bFdmK526rT4I3UG3oxQmpohNQlkJCUo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717585916; c=relaxed/simple; bh=LSDCL93k5vWQ4ROYGbGIImcnUT3CyHzsNKfiQrNTl9E=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=XPdXVR7sXYOKhsL5hrG1VxjeuHrgILWr6c5Yb4ACrAhDwMzOtUVjC6KE+uWdDrox5r4+PwGH7TYgyqsS9Z2SbixfpmdBwJ8wPmxzgB2/HW4I9mLSmAzacDbCSCqdZVAjuR3T0cLdm16HHsynl/ESy4wvTjP+l9GQCk8Udbtd4uY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sina.com; spf=pass smtp.mailfrom=sina.com; arc=none smtp.client-ip=218.30.115.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sina.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=sina.com X-SMAIL-HELO: localhost.localdomain Received: from unknown (HELO localhost.localdomain)([113.118.70.2]) by sina.com (172.16.235.25) with ESMTP id 666047C800003AB0; Wed, 5 Jun 2024 19:11:09 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com Authentication-Results: sina.com; spf=none smtp.mailfrom=hdanton@sina.com; dkim=none header.i=none; dmarc=none action=none header.from=hdanton@sina.com X-SMAIL-MID: 29600134210358 X-SMAIL-UIID: F6B7F59F33754DBFA004D0AA4633AF65-20240605-191109-1 From: Hillf Danton To: Leon Romanovsky Cc: Tejun Heo , Peter Zijlstra , Lai Jiangshan , Zqiang , linux-kernel@vger.kernel.org, Gal Pressman , Tariq Toukan , RDMA mailing list Subject: Re: [PATCH -rc] workqueue: Reimplement UAF fix to avoid lockdep worning Date: Wed, 5 Jun 2024 19:10:55 +0800 Message-Id: <20240605111055.1843-1-hdanton@sina.com> In-Reply-To: <20240604185804.GT3884@unreal> References: <4c4f1fb769a609a61010cb6d884ab2841ef716d3.1716885172.git.leon@kernel.org> <20240531034851.GF3884@unreal> <20240604105456.1668-1-hdanton@sina.com> <20240604113834.GO3884@unreal> Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Tue, 4 Jun 2024 21:58:04 +0300 Leon Romanovsky > On Tue, Jun 04, 2024 at 06:30:49AM -1000, Tejun Heo wrote: > > On Tue, Jun 04, 2024 at 02:38:34PM +0300, Leon Romanovsky wrote: > > > Thanks, it is very rare situation where call to flush/drain queue > > > (in our case kthread_flush_worker) in the middle of the allocation > > > flow can be correct. I can't remember any such case. > > > > > > So even we don't fully understand the root cause, the reimplementation > > > is still valid and improves existing code. > > > > It's not valid. pwq release is async and while wq free in the error path > > isn't. The flush is there so that we finish the async part before > > synchronize error handling. The patch you posted will can lead to double > > free after a pwq allocation failure. We can make the error path synchronous > > but the pwq free path should be updated first so that it stays synchronous > > in the error path. Note that it *needs* to be asynchronous in non-error > > paths, so it's going to be a bit subtle one way or the other. > > But at that point, we didn't add newly created WQ to any list which will execute > that asynchronous release. Did I miss something? > Maybe it is more subtle than thought, but not difficult to make the wq allocation path sync. See if the patch could survive your test. --- x/include/linux/workqueue.h +++ y/include/linux/workqueue.h @@ -402,6 +402,7 @@ enum wq_flags { */ WQ_POWER_EFFICIENT = 1 << 7, + __WQ_INITIALIZING = 1 << 14, /* internal: workqueue is initializing */ __WQ_DESTROYING = 1 << 15, /* internal: workqueue is destroying */ __WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */ __WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */ --- x/kernel/workqueue.c +++ y/kernel/workqueue.c @@ -5080,6 +5080,8 @@ static void pwq_release_workfn(struct kt * is gonna access it anymore. Schedule RCU free. */ if (is_last) { + if (wq->flags & __WQ_INITIALIZING) + return; wq_unregister_lockdep(wq); call_rcu(&wq->rcu, rcu_free_wq); } @@ -5714,8 +5716,10 @@ struct workqueue_struct *alloc_workqueue goto err_unreg_lockdep; } + wq->flags |= __WQ_INITIALIZING; if (alloc_and_link_pwqs(wq) < 0) goto err_free_node_nr_active; + wq->flags &= ~__WQ_INITIALIZING; if (wq_online && init_rescuer(wq) < 0) goto err_destroy; --