linux-kernel - Re: linux-next: umh: fix processed error when UMH_WAIT_PROC is used seems to break linux bridge on s390x (bisected)

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Date:   Wed, 1 Jul 2020 12:08:11 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>, ast@...nel.org,
        axboe@...nel.dk, bfields@...ldses.org,
        bridge@...ts.linux-foundation.org, chainsaw@...too.org,
        christian.brauner@...ntu.com, chuck.lever@...cle.com,
        davem@...emloft.net, dhowells@...hat.com,
        gregkh@...uxfoundation.org, jarkko.sakkinen@...ux.intel.com,
        jmorris@...ei.org, josh@...htriplett.org, keescook@...omium.org,
        keyrings@...r.kernel.org, kuba@...nel.org,
        lars.ellenberg@...bit.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-security-module@...r.kernel.org, nikolay@...ulusnetworks.com,
        philipp.reisner@...bit.com, ravenexp@...il.com,
        roopa@...ulusnetworks.com, serge@...lyn.com, slyfox@...too.org,
        viro@...iv.linux.org.uk, yangtiezhu@...ngson.cn,
        netdev@...r.kernel.org, markward@...ux.ibm.com,
        linux-s390 <linux-s390@...r.kernel.org>
Subject: Re: linux-next: umh: fix processed error when UMH_WAIT_PROC is used
 seems to break linux bridge on s390x (bisected)



On 30.06.20 19:57, Luis Chamberlain wrote:
> On Fri, Jun 26, 2020 at 02:54:10AM +0000, Luis Chamberlain wrote:
>> On Wed, Jun 24, 2020 at 08:37:55PM +0200, Christian Borntraeger wrote:
>>>
>>>
>>> On 24.06.20 20:32, Christian Borntraeger wrote:
>>> [...]> 
>>>> So the translations look correct. But your change is actually a sematic change
>>>> if(ret) will only trigger if there is an error
>>>> if (KWIFEXITED(ret)) will always trigger when the process ends. So we will always overwrite -ECHILD
>>>> and we did not do it before. 
>>>>
>>>
>>> So the right fix is
>>>
>>> diff --git a/kernel/umh.c b/kernel/umh.c
>>> index f81e8698e36e..a3a3196e84d1 100644
>>> --- a/kernel/umh.c
>>> +++ b/kernel/umh.c
>>> @@ -154,7 +154,7 @@ static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
>>>                  * the real error code is already in sub_info->retval or
>>>                  * sub_info->retval is 0 anyway, so don't mess with it then.
>>>                  */
>>> -               if (KWIFEXITED(ret))
>>> +               if (KWEXITSTATUS(ret))
>>>                         sub_info->retval = KWEXITSTATUS(ret);
>>>         }
>>>  
>>> I think.
>>
>> Nope, the right form is to check for WIFEXITED() before using WEXITSTATUS().
>> I'm not able to reproduce this on x86 with a bridge. What type of bridge
>> are you using on a guest, or did you mean using KVM so that the *host*
>> can spawn kvm guests?
>>
>> It would be good if you can try to add a bridge manually and see where
>> things fail. Can you do something like this:
>>
>> brctl addbr br0
>> brctl addif br0 ens6 
>> ip link set dev br0 up
>>
>> Note that most callers are for modprobe. I'd be curious to see which
>> umh is failing which breaks bridge for you. Can you trut this so we can
>> see which umh call is failing?
> 
> Christian, any luck getting to test the code below to see what this
> reveals?
> 
>   Luis

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