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=-5.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 10B21ECE58C for ; Mon, 7 Oct 2019 14:49:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D2E6321479 for ; Mon, 7 Oct 2019 14:49:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D2E6321479 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 6FF938E0005; Mon, 7 Oct 2019 10:49:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6AFC98E0003; Mon, 7 Oct 2019 10:49:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5C59C8E0005; Mon, 7 Oct 2019 10:49:41 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0182.hostedemail.com [216.40.44.182]) by kanga.kvack.org (Postfix) with ESMTP id 3A7E98E0003 for ; Mon, 7 Oct 2019 10:49:41 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id D04EF40E1 for ; Mon, 7 Oct 2019 14:49:40 +0000 (UTC) X-FDA: 76017272520.25.ghost27_7192247ffc649 X-HE-Tag: ghost27_7192247ffc649 X-Filterd-Recvd-Size: 3517 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf50.hostedemail.com (Postfix) with ESMTP for ; Mon, 7 Oct 2019 14:49:39 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 7523EAD45; Mon, 7 Oct 2019 14:49:38 +0000 (UTC) Date: Mon, 7 Oct 2019 16:49:37 +0200 From: Michal Hocko To: Petr Mladek Cc: Qian Cai , akpm@linux-foundation.org, sergey.senozhatsky.work@gmail.com, rostedt@goodmis.org, peterz@infradead.org, linux-mm@kvack.org, john.ogness@linutronix.de, david@redhat.com, linux-kernel@vger.kernel.org, Heiko Carstens , Vasily Gorbik , Christian Borntraeger Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() Message-ID: <20191007144937.GO2381@dhcp22.suse.cz> References: <1570228005-24979-1-git-send-email-cai@lca.pw> <20191007143002.l37bt2lzqtnqjqxu@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191007143002.l37bt2lzqtnqjqxu@pathway.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: [Cc s390 maintainers - the lockdep is http://lkml.kernel.org/r/1570228005-24979-1-git-send-email-cai@lca.pw Petr has explained it is a false positive http://lkml.kernel.org/r/20191007143002.l37bt2lzqtnqjqxu@pathway.suse.cz] On Mon 07-10-19 16:30:02, Petr Mladek wrote: [...] > I believe that it cannot really happen because: > > static int __init > sclp_console_init(void) > { > [...] > rc = sclp_rw_init(); > [...] > register_console(&sclp_console); > return 0; > } > > sclp_rw_init() is called before register_console(). And > console_unlock() will never call sclp_console_write() before > the console is registered. > > AFAIK, lockdep only compares existing chain of locks. It does > not know about console registration that would make some > code paths mutually exclusive. > > I believe that it is a false positive. I do not know how to > avoid this lockdep report. I hope that it will disappear > by deferring all printk() calls rather soon. Thanks a lot for looking into this Petr. I have also checked the code and I really fail to see why the allocation has to be done under the lock in the first place. sclp_read_sccb and sclp_init_sccb are global variables but I strongly suspect that they need a synchronization during early init, callbacks are registered only later IIUC: diff --git a/drivers/s390/char/sclp.c b/drivers/s390/char/sclp.c index d2ab3f07c008..4b1c033e3255 100644 --- a/drivers/s390/char/sclp.c +++ b/drivers/s390/char/sclp.c @@ -1169,13 +1169,13 @@ sclp_init(void) unsigned long flags; int rc = 0; + sclp_read_sccb = (void *) __get_free_page(GFP_ATOMIC | GFP_DMA); + sclp_init_sccb = (void *) __get_free_page(GFP_ATOMIC | GFP_DMA); spin_lock_irqsave(&sclp_lock, flags); /* Check for previous or running initialization */ if (sclp_init_state != sclp_init_state_uninitialized) goto fail_unlock; sclp_init_state = sclp_init_state_initializing; - sclp_read_sccb = (void *) __get_free_page(GFP_ATOMIC | GFP_DMA); - sclp_init_sccb = (void *) __get_free_page(GFP_ATOMIC | GFP_DMA); BUG_ON(!sclp_read_sccb || !sclp_init_sccb); /* Set up variables */ INIT_LIST_HEAD(&sclp_req_queue); -- Michal Hocko SUSE Labs