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=-9.3 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 C3C9DECDE44 for ; Thu, 1 Nov 2018 00:25:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 891CB2064C for ; Thu, 1 Nov 2018 00:25:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="WYQIK3LS" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 891CB2064C 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 S1726700AbeKAJZc (ORCPT ); Thu, 1 Nov 2018 05:25:32 -0400 Received: from mail-ed1-f66.google.com ([209.85.208.66]:40412 "EHLO mail-ed1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726012AbeKAJZa (ORCPT ); Thu, 1 Nov 2018 05:25:30 -0400 Received: by mail-ed1-f66.google.com with SMTP id z12-v6so9411124edp.7 for ; Wed, 31 Oct 2018 17:24:57 -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 :mime-version:content-transfer-encoding; bh=WlrQzTFiPM+4wvhfAOXLKeQLq894q6/wVEpY/LQpVd0=; b=WYQIK3LSCWRZN1/RJ4O00AHkkXlMIfC8IFjqoboe8Q73SIxKXwG2r8n+H0rOa+ZLNS uVPILpHByZ51vP/jktYa/W7RaaKgVNmntlsChbHT06bT/hHN0yuHE91hAz8KhNPyVFiv XbsH2VMNAO+3jGu9JK9jAcud1Vgcp4Q6aL536X7OuaS3tXtJ4jx+zSNQDTyJeP/ayNEp rOdDN5PvXzyM5tarSMRSFvgmZ9V3wDnWfudZH1zu2ueZXvXqf4DbbPKsAAenTv1+ZuG1 AlPyLrWR6X6pUfDqcpWh4XqbodeGZeEYU7nr1T1sd7lWV17NoN94NZhCNYfMonFb6NxB qagw== 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:mime-version:content-transfer-encoding; bh=WlrQzTFiPM+4wvhfAOXLKeQLq894q6/wVEpY/LQpVd0=; b=rHuy4Ow8Gu/gYwfJ+NeO/UFJJJCaCPBkH5lD3b8itSwecSvPJ7Rz37Gzm4goB2Rrg+ bS6uHixMsQfmhz8ETB3XH1jqiqbiPah9mDtHm8b3NvKrthE/TZH+dypENCPPW5V5/pXg pg1pJKlC/wiV5Wkt/ltFNP5SH01P03hwx1JOHFT+/3D01z3h786fOeiaJfA1dvhv+ZS/ JpouTjTIKpDfR+iGE8v+M/JaPbcN13zhNd0Z7iZjT5f2Tor3IrcbzM6vn4eiwlTpGySZ 3Sgc9NHjhdIwru8+HRQuzG4fA+9OzzMBFeU5S/V6QOVc7D6gWEhgLdUsYY9Lpd9A66il VDYA== X-Gm-Message-State: AGRZ1gLga+cQjHXAaNJtLwMe5v/nVDCRxCOnwk7vKAgpDBqhahBBUuvp 2jnYfXjS9p832tDelk+IkG5xjVF0SLA= X-Google-Smtp-Source: AJdET5eNTj9LABD/4aPneQxvHmNhK82an9adOHdaxW3QeBbwxWA40CaxPgn5oJVSHSe1qWdL1ZYvqg== X-Received: by 2002:a17:906:12c6:: with SMTP id l6-v6mr2816246ejb.74.1541031896480; Wed, 31 Oct 2018 17:24:56 -0700 (PDT) Received: from Mindolluin.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id s12-v6sm10188175edd.39.2018.10.31.17.24.55 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 31 Oct 2018 17:24:55 -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 , stable@vger.kernel.org Subject: [PATCHv6 1/7] tty/ldsem: Wake up readers after timed out down_write() Date: Thu, 1 Nov 2018 00:24:46 +0000 Message-Id: <20181101002452.5483-2-dima@arista.com> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20181101002452.5483-1-dima@arista.com> References: <20181101002452.5483-1-dima@arista.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 Cc: stable@vger.kernel.org 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); -- 2.19.1