linux-next: umh: fix processed error when UMH_WAIT_PROC is used seems to break linux bridge on s390x (bisected)

[Christian Borntraeger]

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.