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=-2.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, 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 A0443C04ABB for ; Wed, 12 Sep 2018 00:17:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5A70920866 for ; Wed, 12 Sep 2018 00:17:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="AfBEnBxN" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5A70920866 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 S1728174AbeILFTD (ORCPT ); Wed, 12 Sep 2018 01:19:03 -0400 Received: from mail-ed1-f68.google.com ([209.85.208.68]:33482 "EHLO mail-ed1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726861AbeILFTB (ORCPT ); Wed, 12 Sep 2018 01:19:01 -0400 Received: by mail-ed1-f68.google.com with SMTP id d8-v6so371352edv.0 for ; Tue, 11 Sep 2018 17:17:16 -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=AfBEnBxNhRtFU6Dh8F0nITA42hrLxMA78o5O22BX3H5i4N5c1MNBPgHWAJ+5LobWzj Oy+qPjqJzS6E71ivm0TEssbrGChvrnHpFbH44SsreYsut/UhTFC97reC/YiLHdrZYKAm tifOWCE5NRgvvdp+pib67sAK+1TgEqXb2ahx/hWG5BP+bKpVTqwGUM4J0CQDxEXkQ+w7 WDT1/UeZR4tvypm7RaD9yCvN/9MeZHHtCTgBkh6qNg0J5pcJXC+IudGTaENAElRGpYpg sHbExCoCkLmhduPDITehY502qNPMxOFs2xw2QKb43AD77baxCbYXjTxXUWFurg2Xhw5r W/Vw== 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=hgkhrsCLOXQezu2YhpWp3+T1UlA9D1+ifAkf0/Xlr4WvJrWgzKEgvMOZWl0MRzYT/u BLQpYqvpwas/OgENByEbMz2xfJ4w9dvxuEDoHjkqSovIVTrLv+DH5kpB6cf5G9VNTkNF tszVqwoXUDkF3KMH18+BuClx9nU5NALEYQku8JAFkLVJjEwcihSQMNJ9kfWdm02m1zVe AT1zzqrBO2R9S6Hfpzc7tXbK0JMsomn3AUtgml5CNrSZaVJEjc89EYeGBmUmXhr1Z4Yf W7Lww0WUzde+TY1FsD0+WJIrXg7lr17YTwQvLeObdPDWbo/wotwEBsLZdfGl6Fxu5j0o fZTw== X-Gm-Message-State: APzg51BqOwPFxFTqPhJ+ZvUst6PZQgFjYvXZLjwAh6JKGUWQr+C+UTET /i4MmfvDvwWt/E5OZnwRZGCNu7d1x40= X-Google-Smtp-Source: ANB0VdZrhnAASfm76bUrSscA977tblJV+PKfDYCbqx0/rpTQy3csE28Zbj1ZPlVAUYTODzNTbBRn+g== X-Received: by 2002:a50:aba3:: with SMTP id u32-v6mr29895029edc.257.1536711435387; Tue, 11 Sep 2018 17:17:15 -0700 (PDT) Received: from dhcp.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id l16-v6sm10380593edb.41.2018.09.11.17.17.14 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 11 Sep 2018 17:17:14 -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: [PATCHv4 7/7] tty/ldsem: Decrement wait_readers on timeouted down_read() Date: Wed, 12 Sep 2018 01:17:01 +0100 Message-Id: <20180912001702.18522-8-dima@arista.com> X-Mailer: git-send-email 2.13.6 In-Reply-To: <20180912001702.18522-1-dima@arista.com> References: <20180912001702.18522-1-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