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 A711AECDE44 for ; Thu, 1 Nov 2018 00:25:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C4B42064C for ; Thu, 1 Nov 2018 00:25:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="oLseqnDH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6C4B42064C 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 S1727637AbeKAJZn (ORCPT ); Thu, 1 Nov 2018 05:25:43 -0400 Received: from mail-ed1-f66.google.com ([209.85.208.66]:46534 "EHLO mail-ed1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727485AbeKAJZk (ORCPT ); Thu, 1 Nov 2018 05:25:40 -0400 Received: by mail-ed1-f66.google.com with SMTP id f8-v6so2837052edt.13 for ; Wed, 31 Oct 2018 17:25:07 -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=ZpTN5pGA7IFAwGBczXrryaSm+c6IlC0lW6r8xaAIF8A=; b=oLseqnDHr4p5PB7/ES8hk1xtj9E6ekh/vEPRkxzPe7sRa5WieveThRzItz3Z/LoY/P jAyWk4LZCNVz6OnNQZgvItK6AB/t0pdDzRVcTH1+dVIcE6fKh9XHc4kyTTC7Uz5zvWGl gJek8PSnJA7qgmVEcV96BET7dfyxefWHuYhwXHZ7YTFoGhqYaXfiT9shFgz6EAa02sXR OlWInqZG/cOZQW2Fj7N98MuPP8Y+UTl6Ox9cd5SfKvIkSYoSRPxOyhqlGS2F/VeaDCbB 5hiyxrhzUOxmeogKY2Lwl2YJbnPfJPcYS8+plIpJGEfOnAPGgj+bFBeP7VKjL7wwJ1LY 0M0g== 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=ZpTN5pGA7IFAwGBczXrryaSm+c6IlC0lW6r8xaAIF8A=; b=uKyGcRRev6JDwCaB0IilqBwHnQIyWoouHK1A5x3g0r4blqLCTtmInpjjU7g9zc/Beu PCqSALGDE9V5UK1puUigNDlxp0X3eD19SeBvcu4m6kUEfFoJ2Z+tvVTkwDa38MQaxejc qzxlfd7vwMuEAlLUpgjMG0USZ2q9sp07w8cyiIS61ALrQNwqFjhr78BKTOd12uKRisZJ 8BFE6TTXErHQJ34JEDQOse0bFnpKpBBy4zfMg656c4toMvAGJmNKaO/gcNe4u0U6zodU xdmkz/CUGfGVr45actYYK1arhMhi0RIYp7pL2ZLdcPjzH1agLgE8Wdy2fJ+v3eWTo8Sz qCGQ== X-Gm-Message-State: AGRZ1gL7u/dl0axUYe31wCbGn5wg+53SPEi7sO8+4mXHQhsK4jiYrdec TLvINgo0uDA/n9fi3MoLTlYQiW3lxv0= X-Google-Smtp-Source: AJdET5c4wOFKjJazBTYcLh5V2Z+H2q3Mk/+81MxDV79n6gd3H57gSkYJ159h1Yu/1yxYwVYQTs3kOg== X-Received: by 2002:a17:906:2ec8:: with SMTP id s8-v6mr2795559eji.192.1541031906337; Wed, 31 Oct 2018 17:25:06 -0700 (PDT) Received: from Mindolluin.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id s12-v6sm10188175edd.39.2018.10.31.17.25.04 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 31 Oct 2018 17:25:05 -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: [PATCHv6 7/7] tty/ldsem: Decrement wait_readers on timeouted down_read() Date: Thu, 1 Nov 2018 00:24:52 +0000 Message-Id: <20181101002452.5483-8-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 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); -- 2.19.1