[tip:sched/urgent] init, sched: Fix race between init and kthreadd
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From: tip-bot for Peter Zijlstra on 28 Jun 2010 16:30 Commit-ID: b433c3d4549ae74935b585115f076c6fb7bc48fe Gitweb: http://git.kernel.org/tip/b433c3d4549ae74935b585115f076c6fb7bc48fe Author: Peter Zijlstra <peterz(a)infradead.org> AuthorDate: Mon, 28 Jun 2010 16:51:01 +0200 Committer: Ingo Molnar <mingo(a)elte.hu> CommitDate: Mon, 28 Jun 2010 18:21:30 +0200 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(a)gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl> Acked-by: Linus Torvalds <torvalds(a)linux-foundation.org> LKML-Reference: <1277736661.3561.110.camel(a)laptop> Signed-off-by: Ingo Molnar <mingo(a)elte.hu> --- init/main.c | 12 ++++++++++++ 1 files changed, 12 insertions(+), 0 deletions(-) diff --git a/init/main.c b/init/main.c index 3bdb152..633442f 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(); /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |