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

[Tetsuo Handa]

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()).