linux-kernel - Regression with orderly

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Message-ID: <1363058712.4534.12.camel@pasglop>
Date:	Tue, 12 Mar 2013 14:25:12 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	hongfeng <hongfeng@...vell.com>, david@...son.dropbear.id.au
Subject: Regression with orderly_poweroff()

Hi Linus !

A couple of weeks ago, David sent an email that went unanswered about a
regression concerning orderly_poweroff(). I think the original patch
causing it should be reverted, here's the actual email with the
explanation:

<<<
Subject: orderly_poweroff() is no longer safe in atomic context

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.
>>>

Cheers,
Ben.

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