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 17:48:48 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, 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 01.07.20 17:38, Luis Chamberlain wrote:
> On Wed, Jul 01, 2020 at 11:08:57PM +0900, Tetsuo Handa wrote:
>> On 2020/07/01 22:53, Luis Chamberlain wrote:
>>>> 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).
>>>
>>> br_stp_start() doesn't check for the raw value, it just checks for err
>>> or !err. So the patch, "umh: fix processed error when UMH_WAIT_PROC is
>>> used" propagates the correct error now.
>>
>> No. If "/sbin/bridge-stp virbr0 start" terminated due to e.g. SIGSEGV
>> (for example, by inserting "kill -SEGV $$" into right after "#!/bin/sh" line),
>> br_stp_start() needs to select BR_KERNEL_STP path. We can't assume that
>> /sbin/bridge-stp is always terminated by exit() syscall (and hence we can't
>> ignore KWIFSIGNALED() case in call_usermodehelper_exec_sync()).
> 
> Ah, well that would be a different fix required, becuase again,
> br_stp_start() does not untangle the correct error today really.
> I also I think it would be odd odd that SIGSEGV or another signal 
> is what was terminating Christian's bridge stp call, but let's
> find out!
> 
> Note we pass 0 to the options to wait so the mistake here could indeed
> be that we did not need KWIFSIGNALED(). I was afraid of this prospect...
> as it other implications.
> 
> It means we either *open code* all callers, or we handle this in a
> unified way on the umh. And if we do handle this in a unified way, it
> then begs the question as to *what* do we pass for the signals case and
> continued case. Below we just pass the signal, and treat continued as
> OK, but treating continued as OK would also be a *new* change as well.
> 
> For instance (this goes just boot tested, but Christian if you can
> try this as well that would be appreciated):


Does not help, the bridge stays in DOWN state.