From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:25034 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725956AbgCIJkZ (ORCPT ); Mon, 9 Mar 2020 05:40:25 -0400 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 0299dOAE133991 for ; Mon, 9 Mar 2020 05:40:23 -0400 Received: from e06smtp04.uk.ibm.com (e06smtp04.uk.ibm.com [195.75.94.100]) by mx0b-001b2d01.pphosted.com with ESMTP id 2ym5e1t9gh-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 09 Mar 2020 05:40:23 -0400 Received: from localhost by e06smtp04.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 9 Mar 2020 09:40:21 -0000 Subject: Re: [PATCH net] net/smc: cancel event worker during device removal References: <20200306134518.84416-1-kgraul@linux.ibm.com> <20200308150107.GC11496@unreal> <0b5d992d-2447-1606-f8ce-73801643160a@linux.ibm.com> <20200309080439.GJ11496@unreal> From: Karsten Graul Date: Mon, 9 Mar 2020 10:40:16 +0100 MIME-Version: 1.0 In-Reply-To: <20200309080439.GJ11496@unreal> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: <49a3e4fc-66c3-e658-c95f-6651c4336510@linux.ibm.com> Sender: linux-s390-owner@vger.kernel.org List-ID: To: Leon Romanovsky Cc: davem@davemloft.net, netdev@vger.kernel.org, linux-s390@vger.kernel.org, heiko.carstens@de.ibm.com, raspl@linux.ibm.com, ubraun@linux.ibm.com On 09/03/2020 09:04, Leon Romanovsky wrote: > On Sun, Mar 08, 2020 at 08:59:33PM +0100, Karsten Graul wrote: >> On 08/03/2020 16:01, Leon Romanovsky wrote: >>> On Fri, Mar 06, 2020 at 02:45:18PM +0100, Karsten Graul wrote: >>>> During IB device removal, cancel the event worker before the device >>>> structure is freed. In the worker, check if the device is being >>>> terminated and do not proceed with the event work in that case. >>>> >>>> Fixes: a4cf0443c414 ("smc: introduce SMC as an IB-client") >>>> Reported-by: syzbot+b297c6825752e7a07272@syzkaller.appspotmail.com >>>> Signed-off-by: Karsten Graul >>>> Reviewed-by: Ursula Braun >>>> --- >>>> net/smc/smc_ib.c | 4 ++++ >>>> 1 file changed, 4 insertions(+) >>>> >>>> diff --git a/net/smc/smc_ib.c b/net/smc/smc_ib.c >>>> index d6ba186f67e2..5e4e64a9aa4b 100644 >>>> --- a/net/smc/smc_ib.c >>>> +++ b/net/smc/smc_ib.c >>>> @@ -240,6 +240,9 @@ static void smc_ib_port_event_work(struct work_struct *work) >>>> work, struct smc_ib_device, port_event_work); >>>> u8 port_idx; >>>> >>>> + if (list_empty(&smcibdev->list)) >>>> + return; >>>> + >>> >>> How can it be true if you are not holding "smc_ib_devices.lock" during >>> execution of smc_ib_port_event_work()? >>> >> >> It is true when smc_ib_remove_dev() runs before the work actually started. >> Other than that its only a shortcut to return earlier, when the item is >> removed from the list after the check then the processing just takes a >> little bit longer...its still save. > > The check itself maybe safe, but it can't fix syzkaller bug reported above. > As you said, the smc_ib_remove_dev() can be called immediately after > your list_empty() check and we return to original behavior. > > The correct design will be to ensure that smc_ib_port_event_work() is > executed only smcibdev->list is not empty. > > Thanks > The fix I had in mind was the cancel_work_sync(&smcibdev->port_event_work); to wait for a running port_event_work to finish before smcibdev is freed. I can remove the list_empty() check if that is too confusing. >> >>>> for_each_set_bit(port_idx, &smcibdev->port_event_mask, SMC_MAX_PORTS) { >>>> smc_ib_remember_port_attr(smcibdev, port_idx + 1); >>>> clear_bit(port_idx, &smcibdev->port_event_mask); >>>> @@ -582,6 +585,7 @@ static void smc_ib_remove_dev(struct ib_device *ibdev, void *client_data) >>>> smc_smcr_terminate_all(smcibdev); >>>> smc_ib_cleanup_per_ibdev(smcibdev); >>>> ib_unregister_event_handler(&smcibdev->event_handler); >>>> + cancel_work_sync(&smcibdev->port_event_work); >>>> kfree(smcibdev); >>>> } >>>> >>>> -- >>>> 2.17.1 >>>> >> >> -- >> Karsten >> >> (I'm a dude) >> -- Karsten (I'm a dude)