linux-kernel - Re: Regression with orderly

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Date:	Tue, 12 Mar 2013 14:54:02 -0300
From:	Lucas De Marchi <lucas.de.marchi@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>, david@...son.dropbear.id.au,
	Kees Cook <keescook@...omium.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Feng Hong <hongfeng@...vell.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
Subject: Re: Regression with orderly_poweroff()

On Tue, Mar 12, 2013 at 11:46 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Mon, Mar 11, 2013 at 8:25 PM, Benjamin Herrenschmidt
> <benh@...nel.crashing.org> wrote:
>>
>> 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:
>
> Hmm.. You should really have cc'd the people who acked it and were in
> the sign-off chain too, because all those people are involved with the
> patch as well.
>
> Also, the patch doesn't revert cleanly any more after commit
> 7ff6764061ec ("usermodehelper: cleanup/fix __orderly_poweroff() &&
> argv_free()") which seems to be a real bug-fix for a double free, but
> which really doesn't seem to work together with UMH_NO_WAIT.

Yep, using it in that way with UMH_NO_WAIT will not work.

>
> So before reverting that one too, let's at least get the people who
> were involved with the original patch (and the bugfix that relies on
> it) in the email thread.

I have some pending patches on LKML to remove
call_usermodehelper_fns() and export call_usermodehelper_{setup,exec}.
 Doing this we can separate the allocation part using GFP_ATOMIC in
order to make it work on interrupt context. May I suggest going with
something like below after that patches are applied (sorry, whitespace
damaged)? I can also rework the patch series so this can be applied
regardless of the rest.


Lucas De Marchi

diff --git a/kernel/sys.c b/kernel/sys.c
index bd15276..6df5ec7 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2194,7 +2194,8 @@ static int __orderly_poweroff(void)
  "PATH=/sbin:/bin:/usr/sbin:/usr/bin",
  NULL
  };
- int ret;
+ struct subprocess_info *info;
+ int ret = -ENOMEM;

  argv = argv_split(GFP_ATOMIC, poweroff_cmd, &argc);
  if (argv == NULL) {
@@ -2203,7 +2204,10 @@ static int __orderly_poweroff(void)
  return -ENOMEM;
  }

- ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
+ info = call_usermodehelper_setup(argv[0], argv, envp, GFP_ATOMIC,
+ NULL, NULL, NULL);
+ if (info)
+ ret = call_usermodehelper_exec(info, UMH_WAIT_EXEC);
  argv_free(argv);

  return ret;
--
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