From 572a42d1f4c4dcf686eb7b25741e99e789f8d213 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 28 Jun 2010 16:51:01 +0200 Subject: [PATCH] init, sched: Fix race between init and kthreadd commit b433c3d4549ae74935b585115f076c6fb7bc48fe upstream. 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 Signed-off-by: Peter Zijlstra Acked-by: Linus Torvalds LKML-Reference: <1277736661.3561.110.camel@laptop> Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- init/main.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/init/main.c b/init/main.c index bc109c706486..1eb4bd5f09ac 100644 --- a/init/main.c +++ b/init/main.c @@ -407,16 +407,24 @@ 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); kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns); + complete(&kthreadd_done); unlock_kernel(); /* @@ -841,6 +849,10 @@ 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(); /* -- 2.34.1