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Commit b433c3d4 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

init, sched: Fix race between init and kthreadd 



Ilya reported that on a very slow machine he could reliably
reproduce a race between forking init and kthreadd. We first
fork init so that it  obtains pid-1, however since the scheduler
is already fully running at this point it can preempt and run
the init thread before we spawn and set kthreadd_task.

The init thread can then attempt spawning kthreads without
kthreadd being present which results in an OOPS.

Reported-by: default avatarIlya Loginov <isloginov@gmail.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <1277736661.3561.110.camel@laptop>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 0d98bb26

init/main.c

+12 −0
Original line number Diff line number Diff line
@@ -422,18 +422,26 @@ static void __init setup_command_line(char *command_line) 
 * gcc-3.4 accidentally inlines this function, so use noinline.

 */



static __initdata DECLARE_COMPLETION(kthreadd_done);



static noinline void __init_refok rest_init(void)

	__releases(kernel_lock)

{

	int pid;



	rcu_scheduler_starting();

	/*

	 * We need to spawn init first so that it obtains pid-1, however

	 * the init task will end up wanting to create kthreads, which, if

	 * we schedule it before we create kthreadd, will OOPS.

	 */

	kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);

	numa_default_policy();

	pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);

	rcu_read_lock();

	kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);

	rcu_read_unlock();

	complete(&kthreadd_done);

	unlock_kernel();



	/*
@@ -855,6 +863,10 @@ static noinline int init_post(void) 


static int __init kernel_init(void * unused)

{

	/*

	 * Wait until kthreadd is all set-up.

	 */

	wait_for_completion(&kthreadd_done);

	lock_kernel();



	/*