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    SubjectPlease revert kobject_uevent UMH_NO_WAIT
    Please revert commit f520360d93cdc37de5d972dac4bf3bdef6a7f6a7
    "kobject: don't block for each kobject_uevent".

    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.

    Or keep the UMH_NO_WAIT, and complicate the code to allocate and free
    these resources correctly? 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.


    [PATCH] revert kobject_uevent UMH_NO_WAIT

    Reported-by: Tetsuo Handa <>
    Signed-off-by: Hugh Dickins <>

    lib/kobject_uevent.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- 2.6.30-rc2/lib/kobject_uevent.c 2009-04-08 18:20:24.000000000 +0100
    +++ linux/lib/kobject_uevent.c 2009-04-16 20:31:17.000000000 +0100
    @@ -258,7 +258,7 @@ int kobject_uevent_env(struct kobject *k
    goto exit;

    retval = call_usermodehelper(argv[0], argv,
    - env->envp, UMH_NO_WAIT);
    + env->envp, UMH_WAIT_EXEC);


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