netdev - Re: [PATCH net] net/smc: cancel event worker during device removal

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Message-Id: <0b5d992d-2447-1606-f8ce-73801643160a@linux.ibm.com>
Date:   Sun, 8 Mar 2020 20:59:33 +0100
From:   Karsten Graul <kgraul@...ux.ibm.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, heiko.carstens@...ibm.com,
        raspl@...ux.ibm.com, ubraun@...ux.ibm.com
Subject: Re: [PATCH net] net/smc: cancel event worker during device removal

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@...kaller.appspotmail.com
>> Signed-off-by: Karsten Graul <kgraul@...ux.ibm.com>
>> Reviewed-by: Ursula Braun <ubraun@...ux.ibm.com>
>> ---
>>  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.

>>  	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)