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=-3.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, URIBL_BLOCKED autolearn=ham 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 BC506C10F00 for ; Tue, 2 Apr 2019 14:22:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8A1892084B for ; Tue, 2 Apr 2019 14:22:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="jh+RUIr8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731481AbfDBOW5 (ORCPT ); Tue, 2 Apr 2019 10:22:57 -0400 Received: from mail-it1-f195.google.com ([209.85.166.195]:54491 "EHLO mail-it1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730527AbfDBOWz (ORCPT ); Tue, 2 Apr 2019 10:22:55 -0400 Received: by mail-it1-f195.google.com with SMTP id a190so3867782ite.4; Tue, 02 Apr 2019 07:22:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=BTuuXgow23yAHO5FBRml6rBxyZpkve6TBfv3tPtT1X0=; b=jh+RUIr8uACojozI1ZwNh1fAPIjDUqxfdDpVgzvzoFMKgBWHdlnUpgseUMJbr3YpcR E2MwJLi1sap5ZMDsfdUvR48OUjuSO2ZCnpimRHUd9U6teribvwVkOJjrvVfu7WQqhDtZ WL5PPpMxVvlqoG7+s3fwc6CGopJzENn9ZAKQdf/UtNKFpGxZsmNN7YDEe/YE8FIeeVm/ NH2XwETitiQ9PR9TvhaY9diDWmBxGHozhdJptHPB3pFjGBy/aWrX1u8fiGG31zP2Yrez n+hIL95FkWXQTRsqMz250NVOoCtyEMqnIvAgbEjDekWwCirhDz9j2Hr5cDFfM7Zj8KKG PAnQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=BTuuXgow23yAHO5FBRml6rBxyZpkve6TBfv3tPtT1X0=; b=LRXM6qFYgdKuxR5+V07YSDvYrPMuHd19esKd8NCTLe9lLrIsR6cxlk3wHNGnE6xCFl iqoFjxKUjl0QCJsyOEslDj5vjzWWWmz41/6WpOXJ78gzSHdMRg0LudYGCDFNfGy8vI7T SC2Opt3lGTem2pcW4CIKrMmvlwpIk0eAeC6iN7KP1iCbtSTAO5yNVQiDnkC6TNL9JLZH 30ImqZ3j/QsZJDZIpUhSY+BHDd/xF4fU1vjVU6iHdqtPYAwBunpi8iyumWpZZZhm0k2H 8+YmtzzVul4UIjtyHJ2MjAghuV/lDBG99TZOROeWtGOuqvQ/phNdqO10jHbeUF2vnwDE Okyw== X-Gm-Message-State: APjAAAViKB8GASyncKZo5gBW0kaeenU/v3gQ8FpFnYBTfs/XnpnzXYfx b41HJvHqcamXj1Q+e73c5AhAj10NvS1L1P6wvvo= X-Google-Smtp-Source: APXvYqz6PokoQGCuz6F+HLOuYffRjWrqJ8U5XU/0N541JLlGTSupuCe+KBAkEDQIu8LGBBqJZeqmLexFuz2UBR+BjZE= X-Received: by 2002:a02:5f5b:: with SMTP id r88mr11258459jab.22.1554214974780; Tue, 02 Apr 2019 07:22:54 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Dmitry Safonov <0x7f454c46@gmail.com> Date: Tue, 2 Apr 2019 15:22:43 +0100 Message-ID: Subject: Re: [PATCH 3.16 23/99] tty/ldsem: Wake up readers after timed out down_write() To: Ben Hutchings Cc: open list , stable , Andrew Morton , Denis Kirjanov , Greg Kroah-Hartman , Jiri Slaby , kernel test robot , Dmitry Safonov , Peter Zijlstra Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ben, JFI: I haven't checked your tree, but the same patches set contains fixes that are more important to my mind (looking at 4.9 stable tree): - "tty: Drop tty->count on tty_reopen() failure" commit fe3241679009 - "tty: Hold tty_ldisc_lock() during tty_reopen()" commit 83d817f41070 with follow-up fixup "tty: Don't hold ldisc lock in tty_reopen() if ldisc present" commit d3736d82e816 So, I don't know your policy about choosing backports, but I thought worth to mention those patches as you might like to glance at them. (maybe they are already in your tree) Thanks, Dmitry On Tue, 2 Apr 2019 at 14:44, Ben Hutchings wrote: > > 3.16.65-rc1 review patch. If anyone has any objections, please let me know. > > ------------------ > > From: Dmitry Safonov > > commit 231f8fd0cca078bd4396dd7e380db813ac5736e2 upstream. > > ldsem_down_read() will sleep if there is pending writer in the queue. > If the writer times out, readers in the queue should be woken up, > otherwise they may miss a chance to acquire the semaphore until the last > active reader will do ldsem_up_read(). > > There was a couple of reports where there was one active reader and > other readers soft locked up: > Showing all locks held in the system: > 2 locks held by khungtaskd/17: > #0: (rcu_read_lock){......}, at: watchdog+0x124/0x6d1 > #1: (tasklist_lock){.+.+..}, at: debug_show_all_locks+0x72/0x2d3 > 2 locks held by askfirst/123: > #0: (&tty->ldisc_sem){.+.+.+}, at: ldsem_down_read+0x46/0x58 > #1: (&ldata->atomic_read_lock){+.+...}, at: n_tty_read+0x115/0xbe4 > > Prevent readers wait for active readers to release ldisc semaphore. > > Link: lkml.kernel.org/r/20171121132855.ajdv4k6swzhvktl6@wfg-t540p.sh.intel.com > Link: lkml.kernel.org/r/20180907045041.GF1110@shao2-debian > Cc: Jiri Slaby > Cc: Peter Zijlstra > Reported-by: kernel test robot > Signed-off-by: Dmitry Safonov > Signed-off-by: Greg Kroah-Hartman > Signed-off-by: Ben Hutchings > --- > drivers/tty/tty_ldsem.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > --- a/drivers/tty/tty_ldsem.c > +++ b/drivers/tty/tty_ldsem.c > @@ -306,6 +306,16 @@ down_write_failed(struct ld_semaphore *s > if (!locked) > ldsem_atomic_update(-LDSEM_WAIT_BIAS, sem); > list_del(&waiter.list); > + > + /* > + * In case of timeout, wake up every reader who gave the right of way > + * to writer. Prevent separation readers into two groups: > + * one that helds semaphore and another that sleeps. > + * (in case of no contention with a writer) > + */ > + if (!locked && list_empty(&sem->write_wait)) > + __ldsem_wake_readers(sem); > + > raw_spin_unlock_irq(&sem->wait_lock); > > __set_task_state(tsk, TASK_RUNNING); >