Messages in this thread Patch in this message | | | Subject | [PATCH] init: Fix race between init and kthreadd -v3 | From | Peter Zijlstra <> | Date | Mon, 28 Jun 2010 16:51:01 +0200 |
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On Mon, 2010-06-28 at 16:19 +0200, Ingo Molnar wrote:
> I think you may be using a mutex as a completion in essence. Why not use > completions instead?
Totally forgot about those things.. Yes they fit perfectly.
--- Subject: init: Fix race between init and kthreadd -v2
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> --- init/main.c | 12 ++++++++++++ 1 files changed, 12 insertions(+), 0 deletions(-)
diff --git a/init/main.c b/init/main.c index e2a2bf3..2280f63 100644 --- a/init/main.c +++ b/init/main.c @@ -420,18 +420,26 @@ 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(); /* @@ -847,6 +855,10 @@ 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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