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: <8d714a23-bac4-7631-e5fc-f97c20a46083@i-love.sakura.ne.jp>
Date:   Wed, 1 Jul 2020 23:08:57 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        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 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()).