init, sched: Fix race between init and kthreadd (b433c3d4) · Commits · 戴 / test

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:

Ilya Loginov <isloginov@gmail.com> Signed-off-by:

Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by:

Linus Torvalds <torvalds@linux-foundation.org> LKML-Reference: <1277736661.3561.110.camel@laptop> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

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();

		/*

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