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 2D891C04ABB for ; Wed, 12 Sep 2018 00:17:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D55B620866 for ; Wed, 12 Sep 2018 00:17:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="PVeyOio0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D55B620866 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 S1727982AbeILFS5 (ORCPT ); Wed, 12 Sep 2018 01:18:57 -0400 Received: from mail-ed1-f65.google.com ([209.85.208.65]:33473 "EHLO mail-ed1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726861AbeILFS4 (ORCPT ); Wed, 12 Sep 2018 01:18:56 -0400 Received: by mail-ed1-f65.google.com with SMTP id d8-v6so371266edv.0 for ; Tue, 11 Sep 2018 17:17:11 -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=he0HXqppHUTbBLA6Bjwne6q49IoG3fa5OMEO+oLgI88=; b=PVeyOio0ZzvsZtpnwz7fRCs701dWjIKtDUiimCjSFR3ZoTHXGWXeAHkQcLVUrWb84C O1Yn8zbot2/CO5tga6lZUuqgQogZjV37m9tYKWiYuQqwSi/5/Dc3LVGS1RBuC6p/vhUV jI95NaHH1z+JMiSQPkEmTC02nmCGlp6PqVsjeYJwz60RpO+6bylUhcUUj+gF7QpukdsE TU+dqXGsm3zFu57XeAuqqj5A0iyFfTYEJv2Dy6znZX9BsB84SmI0qbbQgqJuqPPT7hSb HHh0neDRwJgEDrFNPME7yLwL5dPYJj4zujKlYgIfsfPUJox4YrCH4C/hCpVrQTvnRT2S 4lDQ== 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=he0HXqppHUTbBLA6Bjwne6q49IoG3fa5OMEO+oLgI88=; b=Soi6CiIwlGSQaxKxqG0SWhbukd87VXhcxNH7inwtRqL61rS1PpaiyaTSeV8RNRbQ4i x08FTdiek2W7GxxJHJO9Yn2M5diD/J7NRkwJZUwny8BKSZXDsnh4iSWalf6+Q8vzEiVq 9ekw5qtiQIiCoFJjiUOLjVGxm8O9q9YLx3pW3oJo5WMcV4t3uUpNhxxVZJfHjPyVtxRL ObIIQJkdORDVXdWpcISEC91JUDwAe0SkhLEV1HUkVBLXtJIXFznTX2IZg5x7oSp/mKuy VMZ5l1xD3ZCt7lgl8zA1F3DehZzOdmZbbSBePP0JG1n7KiD9XKmC1T54Z7BB/qhkZA/P iSuQ== X-Gm-Message-State: APzg51D/WP+C/ErKQaxX6ffi2Ukj2n3XfamLcQRi+P2kKjLMCL3ZURnz DkttY4x6gBwem3ueB73taBrwh2uf2qk= X-Google-Smtp-Source: ANB0VdZBDId7oP7p4sl2yRKiBJB7l74FHHXqzGPEjutMj4O07YtvBAi7FK5SAhlqB29khDHQ9fseGA== X-Received: by 2002:a50:ba59:: with SMTP id 25-v6mr30764083eds.214.1536711429896; Tue, 11 Sep 2018 17:17:09 -0700 (PDT) Received: from dhcp.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id l16-v6sm10380593edb.41.2018.09.11.17.17.08 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 11 Sep 2018 17:17:09 -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: [PATCHv4 3/7] tty/ldsem: Wake up readers after timed out down_write() Date: Wed, 12 Sep 2018 01:16:57 +0100 Message-Id: <20180912001702.18522-4-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 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 by waking them up. 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 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); -- 2.13.6