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=-2.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_HIGH,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 559D0C6778D for ; Tue, 11 Sep 2018 01:48:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CBCA020645 for ; Tue, 11 Sep 2018 01:48:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="D+Oofkfi" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CBCA020645 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 S1727122AbeIKGpY (ORCPT ); Tue, 11 Sep 2018 02:45:24 -0400 Received: from mail-ed1-f68.google.com ([209.85.208.68]:35591 "EHLO mail-ed1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726562AbeIKGpW (ORCPT ); Tue, 11 Sep 2018 02:45:22 -0400 Received: by mail-ed1-f68.google.com with SMTP id y20-v6so17998270edq.2 for ; Mon, 10 Sep 2018 18:48:32 -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=X9f0tj5vsVUdzhrWKSKjpuy79m2IHGhKE6CbiI4NyPA=; b=D+Oofkfiv7u58Olx2NamFEWRP6f+OmHYsojL+U0XZFWru/5Y2T3pzYHlXRlU+x8Y1v FKZeH7IeGUoHBVD87lqcM48NfBICJldiJ0HKwh4Jl4nXLYd6Sddl+u3fe/pVWZZTi3zH rBgJfQXPMkNEijhZ5ENFnZcA2QJCuQiW7lAbi8MQzYjf1mWSjtqLmpAE+WGOzNedzM4E PGLP5kytHhxacd9OwoOYzlQg/AXkSExOuK3vqyWOz+e3qCa0BYPprEmiWfSBb+bdLAfl +kV2SJubej5NU7d04pf0OVKTmRsx5sJv6iTKH6sFT8I7QzFIiniomNWMV4zDc96MKTJq DEnw== 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=X9f0tj5vsVUdzhrWKSKjpuy79m2IHGhKE6CbiI4NyPA=; b=IkjrlEZICLil+uST8NJb2qzTGVs+70Ueqky374/OeOIl/tLBNLzW+h/1PUouuG5Jkp fJtT56JsgqwiKdSkah4FSyerMIPDBwZ2e/YEkgAHIg8Um3mvqbT14rM7I4IC5Bw9736M IsGNJlUZ3qiZ5iJZKHGmQ5v1t65G9uoTywShPRO2vfGGfFWfuzIl6TFtJTdUNC+7EzMU YAUEy5/tcRKr0ypGMFBYq2jIIuu8GYSqrhf57vdkwIeKtmVBgtVjHfiGzea+2AYCz6JO NiD0Y3v31fxREub5ZGtGQAsaNfoGpCpFg4Tn5Uk8PcS35yIsNy8pkJYQ3Xgeg//+HG7O jbTA== X-Gm-Message-State: APzg51CCH9a8raMTPvHJC/CPgtbQ9kDcPe01C+CJtrlVTvML3d6OMPBT 780SxJzKsH6RWzi1b8G9t5MbACUXSeU= X-Google-Smtp-Source: ANB0VdZLZvCQaBT3bzV6BThY3aRtLhuMBMN3imrFJ+TQfETDIJSm5nB1I6Ot85dXRzgreI4Jn6oJJQ== X-Received: by 2002:a50:9622:: with SMTP id y31-v6mr25698927eda.141.1536630511823; Mon, 10 Sep 2018 18:48:31 -0700 (PDT) Received: from dhcp.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id x22-v6sm9171002edb.8.2018.09.10.18.48.30 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 10 Sep 2018 18:48:30 -0700 (PDT) From: Dmitry Safonov To: linux-kernel@vger.kernel.org Cc: Dmitry Safonov <0x7f454c46@gmail.com>, Dmitry Safonov , Daniel Axtens , Dmitry Vyukov , Michael Neuling , Mikulas Patocka , Nathan March , =?UTF-8?q?Pasi=20K=C3=A4rkk=C3=A4inen?= , Peter Hurley , "Rong, Chen" , Sergey Senozhatsky , Tan Xiaojun , Tetsuo Handa , Greg Kroah-Hartman , Jiri Slaby Subject: [PATCHv3 6/6] tty/ldsem: Decrement wait_readers on timeouted down_read() Date: Tue, 11 Sep 2018 02:48:21 +0100 Message-Id: <20180911014821.26286-7-dima@arista.com> X-Mailer: git-send-email 2.13.6 In-Reply-To: <20180911014821.26286-1-dima@arista.com> References: <20180911014821.26286-1-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 832accbbcb6d..f7966ab7b450 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -237,6 +237,7 @@ 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