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| author | Peter Zijlstra <peterz@infradead.org> | 2010-06-28 16:51:01 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2010-06-28 18:21:30 +0200 |
| commit | b433c3d4549ae74935b585115f076c6fb7bc48fe (patch) | |
| tree | fa69951fe2dcdfed7482976d6d6fc0a0bd5d1d5d | |
| parent | 0d98bb2656e9bd2dfda2d089db1fe1dbdab41504 (diff) | |
| download | lwn-b433c3d4549ae74935b585115f076c6fb7bc48fe.tar.gz lwn-b433c3d4549ae74935b585115f076c6fb7bc48fe.zip | |
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>
| -rw-r--r-- | init/main.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/init/main.c b/init/main.c index 3bdb152f412f..633442f79e90 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(); /* |