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=-9.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 15009ECE563 for ; Mon, 17 Sep 2018 23:53:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C090B20C0E for ; Mon, 17 Sep 2018 23:53:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="Sx2HcmVm" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C090B20C0E Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=arista.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728787AbeIRFWt (ORCPT ); Tue, 18 Sep 2018 01:22:49 -0400 Received: from mail-ed1-f68.google.com ([209.85.208.68]:36852 "EHLO mail-ed1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725952AbeIRFWq (ORCPT ); Tue, 18 Sep 2018 01:22:46 -0400 Received: by mail-ed1-f68.google.com with SMTP id f4-v6so392440edq.3 for ; Mon, 17 Sep 2018 16:53:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arista.com; s=googlenew; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=wqltNY8k7Rov893LK2+c57lHF/MKn3vl6wo65bAnJB4=; b=Sx2HcmVmHhkyjpOf/iA0BIUwfhZKzrjGwk+YcFpEwNDc/fqEa7qfy7J3XcS9ayZvVj oDn73pu962z51cNzKYS0P3N7LYP/bE+O2oL0odSNnUxW4B7xY8BA50bPcTRWOSV0VeUZ qYLneGMquHwjiWwgu1LmEkrgPDIIetX+6EQ6GJ4p7/ber43SyqRWmGe9Xj3vNL2P4h5X 4V8/Z95YNIbYQqidb4JYYII6V8RVqFwzexGw8eJgsqz+r4dTt//15Y10Il7w71aAPEuU r6ZFLdQD0sqjjU/HDfhkKbIS0GXts8kTGaVc/ZCL5GixMy0XHT0C/aQ8Vjiin2BjFaNy rg4g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=wqltNY8k7Rov893LK2+c57lHF/MKn3vl6wo65bAnJB4=; b=rLuypNl1oZj1JUSKjC9FCoVb6I357sDPHOXJbEpdAQwnejmd4RnbkBdI5h0OKM8kTo 4mew0/BHWy6XeHXBAmJSxlwoljuCZCnlb3AOIfXWX//27B7i5P3pva8eG+lEKlA7HARE 4LIBmC4+ivdmCtJQei3crCvtuzrEfDn+tJQoxZTDQWmTZxuEunRNRi9IyjRH2hecG1Ny VCGi1gbHVfQf4Adkw/fgoSKoM6njPXT7qE5afZ7ugHsWDfE1hsXnW1fY4hmfXHyTSnZi zmE/7pBl7GpYnChPR4OtQ07SN+Ycqcj58DXiDam/NgU4E653aQYo7L0QjuvqEnrFFgFO cloQ== X-Gm-Message-State: APzg51BaffvMxva6rNEeRm/aqutZXfT48Z1hvxxaxv+3VPybss5lDVsQ anzY6f4I1iIUX/emNPzfZOHxqVpp45A= X-Google-Smtp-Source: ANB0Vda8ZFP2cZPXWGJi4evFWxyRkZMZ5gZvBKA8xXaYGSiBvup4XhIo30GKTUzHqbA26t3iP4W+CA== X-Received: by 2002:a50:aa83:: with SMTP id q3-v6mr47210828edc.64.1537228383506; Mon, 17 Sep 2018 16:53:03 -0700 (PDT) Received: from dhcp.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id r35-v6sm7193912edr.59.2018.09.17.16.53.02 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 17 Sep 2018 16:53:02 -0700 (PDT) From: Dmitry Safonov To: linux-kernel@vger.kernel.org Cc: Dmitry Safonov <0x7f454c46@gmail.com>, Dmitry Safonov , Daniel Axtens , Dmitry Vyukov , Mark Rutland , Michael Neuling , Mikulas Patocka , Nathan March , =?UTF-8?q?Pasi=20K=C3=A4rkk=C3=A4inen?= , Peter Hurley , Peter Zijlstra , "Rong, Chen" , Sergey Senozhatsky , Tan Xiaojun , Tetsuo Handa , Greg Kroah-Hartman , Jiri Slaby Subject: [PATCHv5 2/7] tty/ldsem: Wake up readers after timed out down_write() Date: Tue, 18 Sep 2018 00:52:53 +0100 Message-Id: <20180917235258.5719-3-dima@arista.com> X-Mailer: git-send-email 2.13.6 In-Reply-To: <20180917235258.5719-1-dima@arista.com> References: <20180917235258.5719-1-dima@arista.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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: Greg Kroah-Hartman Cc: Jiri Slaby Cc: Peter Zijlstra Reported-by: kernel test robot Signed-off-by: Dmitry Safonov --- drivers/tty/tty_ldsem.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c index 0c98d88f795a..b989ca26fc78 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -293,6 +293,16 @@ down_write_failed(struct ld_semaphore *sem, long count, long timeout) if (!locked) atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count); 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_current_state(TASK_RUNNING); -- 2.13.6