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 A25DEECE563 for ; Mon, 17 Sep 2018 23:53:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5C251214AB for ; Mon, 17 Sep 2018 23:53:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="RCMbsVvx" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5C251214AB 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 S1728991AbeIRFXA (ORCPT ); Tue, 18 Sep 2018 01:23:00 -0400 Received: from mail-ed1-f65.google.com ([209.85.208.65]:46096 "EHLO mail-ed1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725952AbeIRFWx (ORCPT ); Tue, 18 Sep 2018 01:22:53 -0400 Received: by mail-ed1-f65.google.com with SMTP id k14-v6so349761edr.13 for ; Mon, 17 Sep 2018 16:53:11 -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=DPpt0f/8LcZSCa9NDagMFTu6e0WQH286AZEzI/uklGw=; b=RCMbsVvxwUsTuEdUHueXzKB9PcShBqstZRSP/ekeNrqErU2tngNdcmp3WNgoFTqyah EW4zFt2wKj072z30v+0ZAKaa6tx70lBsFzclgwwOIERxSORtz8HaziseUvDJPwsndO/H 801zFw6+Ooht1T/R80+LCz4nwNeu+QxPA6P8r3GjyLE+jl3qI2VBaaRL5AZAMuGlEqKF 0BFbw+0pCVW25UOrW+nw1rr/wO8a80g21Af6X1XscYTB/YuomMdCRaBa2ySe2qK+x4yq A2hmyZ08pVErobju7JjQnbiBqlusWW0s/RbaGtUC9iY4gFebpQeAZV+sMkWiFT4x870t d/BQ== 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=DPpt0f/8LcZSCa9NDagMFTu6e0WQH286AZEzI/uklGw=; b=DBYLbhr4ToYlasu1XN+oj7ujvD+31SWXuwc6+Ou1Cu6nzFNdUG2dNs3KjaloLtaODi H5h8luBog4wJ5v5fGLbWy199n0c2EsjX0SI4QE7FuSk2KzDK4TTuGo+9NfqvSRLCyjgS 9xMKN+Td5iggcoGR2yRdzlAvwNHVZINNWKMvQP3skiHBZfKv9wGEDyRpfIaoleJei1A7 DbVKuTeztwpCnXKCVgj06mNGdx55GJd1fWf+EniZRXqstMcmGtbCskXa57pOIQ1Iv4VD OSj/ZlQNJ1PrUM0ZLkAhoZ6rosWWa3igxySQxaVBHNvl0n6FB7Oez4r16u/bg/6FV1mj SYPQ== X-Gm-Message-State: APzg51DKIYYf+g7hv0QYhfM0SYv2/mCfWrz2r7p4BUfRZOCrMIcjKeNw xMREWsHuMC9pmQCtpfxn67fowPJDfyw= X-Google-Smtp-Source: ANB0VdYHa4Z7MI7nr2urSo8nnUcaTdCxl8e8IBnH7a1RFz54ls1qAUNYxSodqqEzoO2aPPKfg35e5A== X-Received: by 2002:a50:ade6:: with SMTP id b35-v6mr24754702edd.168.1537228390296; Mon, 17 Sep 2018 16:53:10 -0700 (PDT) Received: from dhcp.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id r35-v6sm7193912edr.59.2018.09.17.16.53.09 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 17 Sep 2018 16:53:09 -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 7/7] tty/ldsem: Decrement wait_readers on timeouted down_read() Date: Tue, 18 Sep 2018 00:52:58 +0100 Message-Id: <20180917235258.5719-8-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 It seems like when ldsem_down_read() fails with timeout, it misses update for sem->wait_readers. By that reason, when writer finally releases write end of the semaphore __ldsem_wake_readers() does adjust sem->count with wrong value: sem->wait_readers * (LDSEM_ACTIVE_BIAS - LDSEM_WAIT_BIAS) I.e, if update comes with 1 missed wait_readers decrement, sem->count will be 0x100000001 which means that there is active reader and it'll make any further writer to fail in acquiring the semaphore. It looks like, this is a dead-code, because ldsem_down_read() is never called with timeout different than MAX_SCHEDULE_TIMEOUT, so it might be worth to delete timeout parameter and error path fall-back.. Cc: Greg Kroah-Hartman Cc: Jiri Slaby Signed-off-by: Dmitry Safonov --- drivers/tty/tty_ldsem.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c index d4d0dbf4a6d9..717292c1c0df 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -212,6 +212,7 @@ down_read_failed(struct ld_semaphore *sem, long count, long timeout) raw_spin_lock_irq(&sem->wait_lock); if (waiter.task) { atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count); + sem->wait_readers--; list_del(&waiter.list); raw_spin_unlock_irq(&sem->wait_lock); put_task_struct(waiter.task); -- 2.13.6