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: <eb0b2ec2-52db-81a4-11b0-c0112b39a7aa@de.ibm.com>
Date:   Wed, 1 Jul 2020 18:01:59 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        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 17:58, Luis Chamberlain wrote:
[...]

>>>
>>> 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. 
> 
> OK thanks for testing, that was fast! Does your code go through the
> STP kernel path or userpath? If it is taking the STP kernel path
> then this is not the real culprit to your issue then.

I have no idea and I cannot look into this right now. I can test
patches as compile,reboot and test is almost no effort.

FWIW, this is just the network of a KVM guest of libvirts default network
no longer working, maybe you can reproduce this on x86 as well?