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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Message-ID: <a6792135-3285-0861-014e-3db85ea251dc@i-love.sakura.ne.jp>
Date:   Wed, 1 Jul 2020 22:24:29 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        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 2020/07/01 19:08, Christian Borntraeger wrote:
> 
> 
> 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);

Well, it is not br_stp_call_user() but br_stp_start() which is expecting
to set sub_info->retval for both KWIFEXITED() case and KWIFSIGNALED() case.
That is, sub_info->retval needs to carry raw value (i.e. without "umh: fix
processed error when UMH_WAIT_PROC is used" will be the correct behavior).