From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:59026 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725796AbgCIIEp (ORCPT ); Mon, 9 Mar 2020 04:04:45 -0400 Date: Mon, 9 Mar 2020 10:04:39 +0200 From: Leon Romanovsky Subject: Re: [PATCH net] net/smc: cancel event worker during device removal Message-ID: <20200309080439.GJ11496@unreal> References: <20200306134518.84416-1-kgraul@linux.ibm.com> <20200308150107.GC11496@unreal> <0b5d992d-2447-1606-f8ce-73801643160a@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0b5d992d-2447-1606-f8ce-73801643160a@linux.ibm.com> Sender: linux-s390-owner@vger.kernel.org List-ID: To: Karsten Graul 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 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 > > >> 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) >