From 05f54c13cd0c33694eec39a265475c5d6cf223cf Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hugh@veritas.com>
Date: Thu, 16 Apr 2009 21:55:29 +0100
Subject: [PATCH] Revert "kobject: don't block for each kobject_uevent".

This reverts commit f520360d93cdc37de5d972dac4bf3bdef6a7f6a7.

Tetsuo Handa, running a kernel with CONFIG_DEBUG_PAGEALLOC=y and
CONFIG_UEVENT_HELPER_PATH=/sbin/hotplug, has been hitting RCU detected
CPU stalls: it's been spinning in the loop where do_execve() counts up
the args (but why wasn't fixup_exception working? dunno).

The recent change, switching kobject_uevent_env() from UMH_WAIT_EXEC
to UMH_NO_WAIT, is broken: the exec uses args on the local stack here,
and an env which is kfreed as soon as call_usermodehelper() returns.
It very much needs to wait for the exec to be done.

An alternative would be to keep the UMH_NO_WAIT, and complicate the code
to allocate and free these resources correctly? but no, as GregKH
pointed out when making the commit, CONFIG_UEVENT_HELPER_PATH="" is a
much better optimization - though some distros are still saying
/sbin/hotplug in their .config, yet with no such binary in their initrd
or their root.

Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: Will Newton <will.newton@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 lib/kobject_uevent.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index 97a777ad4f59..dafeecf5b143 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -258,7 +258,7 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 			goto exit;
 
 		retval = call_usermodehelper(argv[0], argv,
-					     env->envp, UMH_NO_WAIT);
+					     env->envp, UMH_WAIT_EXEC);
 	}
 
 exit:
-- 
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