orderly_poweroff() is no longer safe in atomic context

From: David Gibson
Date: Wed Feb 27 2013 - 00:37:44 EST

Commit 6c0c0d4d1080840eabb3d055d2fd81911111c5fd "poweroff: fix bug in
orderly_poweroff()" apparently fixes one bug in orderly_poweroff(),
but introduces another. The comments on orderly_poweroff() claim it
can be called from any context - and indeed we call it from interrupt
context in arch/powerpc/platforms/pseries/ras.c for example. But
since that commit this is no longer safe, since
call_usermodehelper_fns() is not safe in interrupt context without the
UMH_NO_WAIT option.

I'm having trouble understanding the commit message to see what the
original bug being fixed was. Specifically I can't make sense of:

| The bug here is, step 1 is always successful with param
| UMH_NO_WAIT, which obey the design goal of orderly_poweroff.

And without understanding the original bug, I'm not sure what the
correct fix is.

David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!

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