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: <20200626090001.GA30103@infradead.org>
Date:   Fri, 26 Jun 2020 10:00:01 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        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 Fri, Jun 26, 2020 at 07:22:34AM +0200, Christian Borntraeger wrote:
> 
> 
> On 26.06.20 04:54, 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().
> 
> But this IS a change over the previous code, no?
> I will test next week as I am travelling right now. 

I'm all for reverting back to the previous behavior.  If someone wants
a behavior change it should be a separate patch.  And out of pure self
interest I'd like to see that change after my addition of the
kernel_wait helper to replace the kernel_wait4 abuse :)