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 X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 50FC7C2D0A3 for ; Tue, 3 Nov 2020 20:59:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 176942053B for ; Tue, 3 Nov 2020 20:59:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604437174; bh=j43P6qp85e/ygXkNNIca/FOFKaOvVJMudsEesMHcvBM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=AHl/sg2MBEZegwE0bAuzLn6ZKYdj0H8AJINeQbdu4aRkI9rG4tPIAFJHDTKiGk+it fq0BBYekYnFBZyCbCzG25ECOfSuYn6rFD4AmTrWB5Yl++Y5gUTLiRFifr0TqA5OdgD CtYtUrFA+R9sJiS6oh9e9yeoC/7w/mK4Ih4832k0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733120AbgKCU7d (ORCPT ); Tue, 3 Nov 2020 15:59:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:34626 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731817AbgKCU72 (ORCPT ); Tue, 3 Nov 2020 15:59:28 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 337EF2053B; Tue, 3 Nov 2020 20:59:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604437167; bh=j43P6qp85e/ygXkNNIca/FOFKaOvVJMudsEesMHcvBM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=aVmPhQztxBtXniz89zfpfZZxox+dfgbcMovRI9924/sN4EGeNAlotL9ju2/OC/xen 0rQGG1pR9ZobpcIyyoZf36+Y82tYHs7JCm34IgTub/np/gH+Ai1N19/6QLNeUQpH+c M8BkYxpXjZlJcJ3hIarLLr83rEq1K8KcnLcWrB6M= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Zhihao Cheng , syzbot+853639d0cb16c31c7a14@syzkaller.appspotmail.com, Richard Weinberger Subject: [PATCH 5.4 175/214] ubi: check kthread_should_stop() after the setting of task state Date: Tue, 3 Nov 2020 21:37:03 +0100 Message-Id: <20201103203307.130230296@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201103203249.448706377@linuxfoundation.org> References: <20201103203249.448706377@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Zhihao Cheng commit d005f8c6588efcfbe88099b6edafc6f58c84a9c1 upstream. A detach hung is possible when a race occurs between the detach process and the ubi background thread. The following sequences outline the race: ubi thread: if (list_empty(&ubi->works)... ubi detach: set_bit(KTHREAD_SHOULD_STOP, &kthread->flags) => by kthread_stop() wake_up_process() => ubi thread is still running, so 0 is returned ubi thread: set_current_state(TASK_INTERRUPTIBLE) schedule() => ubi thread will never be scheduled again ubi detach: wait_for_completion() => hung task! To fix that, we need to check kthread_should_stop() after we set the task state, so the ubi thread will either see the stop bit and exit or the task state is reset to runnable such that it isn't scheduled out indefinitely. Signed-off-by: Zhihao Cheng Cc: Fixes: 801c135ce73d5df1ca ("UBI: Unsorted Block Images") Reported-by: syzbot+853639d0cb16c31c7a14@syzkaller.appspotmail.com Signed-off-by: Richard Weinberger Signed-off-by: Greg Kroah-Hartman --- drivers/mtd/ubi/wl.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) --- a/drivers/mtd/ubi/wl.c +++ b/drivers/mtd/ubi/wl.c @@ -1629,6 +1629,19 @@ int ubi_thread(void *u) !ubi->thread_enabled || ubi_dbg_is_bgt_disabled(ubi)) { set_current_state(TASK_INTERRUPTIBLE); spin_unlock(&ubi->wl_lock); + + /* + * Check kthread_should_stop() after we set the task + * state to guarantee that we either see the stop bit + * and exit or the task state is reset to runnable such + * that it's not scheduled out indefinitely and detects + * the stop bit at kthread_should_stop(). + */ + if (kthread_should_stop()) { + set_current_state(TASK_RUNNING); + break; + } + schedule(); continue; }