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authorPeter Zijlstra <peterz@infradead.org>2010-06-28 16:51:01 +0200
committerIngo Molnar <mingo@elte.hu>2010-06-28 18:21:30 +0200
commitb433c3d4549ae74935b585115f076c6fb7bc48fe (patch)
treefa69951fe2dcdfed7482976d6d6fc0a0bd5d1d5d /init
parent0d98bb2656e9bd2dfda2d089db1fe1dbdab41504 (diff)
downloadlinux-linaro-android-b433c3d4549ae74935b585115f076c6fb7bc48fe.tar.gz
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: 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>
Diffstat (limited to 'init')
-rw-r--r--init/main.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/init/main.c b/init/main.c
index 3bdb152f412..633442f79e9 100644
--- a/init/main.c
+++ b/init/main.c
@@ -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();
/*