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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 67DBDC433F5 for ; Thu, 29 Sep 2022 16:40:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235871AbiI2QkU (ORCPT ); Thu, 29 Sep 2022 12:40:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39224 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235729AbiI2QkK (ORCPT ); Thu, 29 Sep 2022 12:40:10 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A2269237D1 for ; Thu, 29 Sep 2022 09:40:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1664469603; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=L6vXI1WS0UxzQeZpA4OgRrRLeEgBfGYudqcjKdjRj7M=; b=TJu5WBQlN7rYlZSGpbBnpQwfU39CO66Qg3tONs0XE8Wtmq8G7Om3OCmm8oblHwIeOaPhgo ZT/6jLk9UNq0HkFV/sv6Ik8575MCR/sIKy69ftC1Q5ujGuUGEDpATRQk7IpEs8Q8AyMk0q GJ0uqUbkfWPBAU93VXOELHaT3DfVfhg= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-582-6I3q8TJ0Pm2bKTmHsCLDzQ-1; Thu, 29 Sep 2022 12:40:00 -0400 X-MC-Unique: 6I3q8TJ0Pm2bKTmHsCLDzQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9C5FB85A5B6; Thu, 29 Sep 2022 16:39:59 +0000 (UTC) Received: from localhost (unknown [10.22.11.90]) by smtp.corp.redhat.com (Postfix) with ESMTP id F310F1731B; Thu, 29 Sep 2022 16:39:58 +0000 (UTC) Date: Thu, 29 Sep 2022 13:39:57 -0300 From: "Luis Claudio R. Goncalves" To: Ulf Hansson Cc: "dinggao.pan" , "bigeasy@linutronix.de" , "tglx@linutronix.de" , "rostedt@goodmis.org" , "ming.yu" , "yunqian.wang" , "linux-mmc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-rt-users@vger.kernel.org" Subject: Re: [PATCH RFC stable 4.14 1/1] mmc: core: fix hung task caused by race condition on context_info Message-ID: References: <21f604139a9a4675b9ed49292839dcfb@horizon.ai> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 29, 2022 at 02:41:26PM +0200, Ulf Hansson wrote: > On Mon, 5 Sept 2022 at 08:22, dinggao.pan wrote: > > > > Hi, > > After applying rt patches to our 4.14 kernel and enabling preempt-rt, we met a hung task during boot caused by race condition on context_info stored in struct mmc_host. > > From our investigation, context_info should not be changed by threads that have not claimed the host, hence the following fix. > > > > Any comments are much appreciated. > > Dinggao Pan > > Hi Dinggao, > > Apologize for the delay. > > The 4.14 kernel is too old for me to be able to comment. In > particular, the mmc block layer moved to blk-mq in v4.16, which means > the path you are investigating doesn't exist any more, sorry. And the new code has the queue operations protected by a spinlock (queue_lock), which I believe is necessary to fix the issue reported here. Luis > Kind regards > Uffe > > > > > From: "Dinggao Pan" > > > > 　　A race condition happens under following circumstances: > > (mmc_thread1) | (mmc_thread2) > > mmc_issue_rq(req1) | > > > qcnt++ for req1 | > > host handling req1 | > > mmc_queue_thread(req=null) | > > > enter queue thread | > > again, fetches blk req | > > (return null), sets | > > is_waiting_last_req 1 | mmc_request_fn(req1) -> set is_new_req 1 > > | and wake_up wait_queue > > mmc_issue_rq(req2) | > mmc_thread2 tries to claim host > > > **qcnt++ for req2** | > > mmc_finalize_req(req2) | > > > should wait for req1 | > > done but req2 return | > > MMC_BLK_NEW_REQ | > > due to is_new_req | > > already set to 1 | > > | > > | > > req1 done | > > > qcnt-- for req1 | > > mmc_issue_rq(req3) | > > > qcnt++ for req3 | > > req2 is not handled but qcnt is already added(noted by **), > > thus mmc_thread1 will never release host, causing mmc_threads > > except thread1 to hung. Fix race by moving wake_up to the front of > > context_info update. > > > > Reviewed By: Yunqian Wang > > Signed-off-by: Dinggao Pan > > Signed-off-by: Ming Yu > > --- > > drivers/mmc/core/queue.c | 7 +++++-- > > 1 file changed, 5 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/mmc/core/queue.c b/drivers/mmc/core/queue.c > > index 0a4e77a5b..58318c102 100644 > > --- a/drivers/mmc/core/queue.c > > +++ b/drivers/mmc/core/queue.c > > @@ -107,6 +107,11 @@ static void mmc_request_fn(struct request_queue *q) > > return; > > } > > > > + if (mq->asleep) { > > + wake_up_process(mq->thread); > > + return; > > + } > > + > > cntx = &mq->card->host->context_info; > > > > if (cntx->is_waiting_last_req) { > > @@ -114,8 +119,6 @@ static void mmc_request_fn(struct request_queue *q) > > wake_up_interruptible(&cntx->wait); > > } > > > > - if (mq->asleep) > > - wake_up_process(mq->thread); > > } > > > > static struct scatterlist *mmc_alloc_sg(int sg_len, gfp_t gfp) > > -- > > 2.36.1 > ---end quoted text---