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 675C9C388F9 for ; Tue, 3 Nov 2020 21:49:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1817221556 for ; Tue, 3 Nov 2020 21:49:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604440168; bh=W/wWV///xM5VSgh9MqitXakSYutwEYqy9wk82CiwRDU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=TmfswhNV/uMexhQMIQ05DXynMeCa4VLFtDTCHAP9YKsWoZLFA6PdYSbAACT6kUO/y NWVhCzSXobI5k5c7u9i4aPGANf68hv7PJuPrpVWg8gnknhGQc32tz5aed+3B7pdJk7 JZd2NvdjDmSVQswJ3LwfTpHUDKA/ZpSDZKg45j2w= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731819AbgKCVt0 (ORCPT ); Tue, 3 Nov 2020 16:49:26 -0500 Received: from mail.kernel.org ([198.145.29.99]:42866 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731188AbgKCUti (ORCPT ); Tue, 3 Nov 2020 15:49:38 -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 0F63020719; Tue, 3 Nov 2020 20:49:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604436578; bh=W/wWV///xM5VSgh9MqitXakSYutwEYqy9wk82CiwRDU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=k2ameiwGFfqo7Mgof+ZnTcTRsH1qFzgfKm9vD3xv3TyukM7Cb33pdIi3NrGZigXX6 +FBhvUMuYDf0bZS/jQXB0Nkdf8Cn+w7ppNnod+5yGVnhf2Stov46QfRLbJ0cM7B5qw jWh3CuxsB7cJrqZy5TNDUBLoW2lZaY+I+qikNQQU= 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 5.9 312/391] ubi: check kthread_should_stop() after the setting of task state Date: Tue, 3 Nov 2020 21:36:03 +0100 Message-Id: <20201103203408.163282671@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201103203348.153465465@linuxfoundation.org> References: <20201103203348.153465465@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 @@ -1639,6 +1639,19 @@ 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; }