From: Oleg Nesterov Date: Wed, 4 Jun 2014 23:12:19 +0000 (-0700) Subject: kthreads: kill CLONE_KERNEL, change kernel_thread(kernel_init) to avoid CLONE_SIGHAND X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=34a1b7236ad6113883f6c448d1da854cad60265e;p=deliverable%2Flinux.git kthreads: kill CLONE_KERNEL, change kernel_thread(kernel_init) to avoid CLONE_SIGHAND 1. Remove CLONE_KERNEL, it has no users and it is dangerous. The (old) comment says "List of flags we want to share for kernel threads" but this is not true, we do not want to share ->sighand by default. This flag can only be used if the caller is sure that both parent/child will never play with signals (say, allow_signal/etc). 2. Change rest_init() to clone kernel_init() without CLONE_SIGHAND. In this case CLONE_SIGHAND does not really hurt, and it looks like optimization because copy_sighand() can avoid kmem_cache_alloc(). But in fact this only adds the minor pessimization. kernel_init() is going to exec the init process, and de_thread() will need to unshare ->sighand and do kmem_cache_alloc(sighand_cachep) anyway, but it needs to do more work and take tasklist_lock and siglock. Signed-off-by: Oleg Nesterov Acked-by: Peter Zijlstra Acked-by: Steven Rostedt Cc: Frederic Weisbecker Cc: Ingo Molnar Cc: Mathieu Desnoyers Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/include/linux/sched.h b/include/linux/sched.h index 611676fd4c2c..8fcd0e6098d9 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -136,12 +136,6 @@ struct filename; #define VMACACHE_SIZE (1U << VMACACHE_BITS) #define VMACACHE_MASK (VMACACHE_SIZE - 1) -/* - * List of flags we want to share for kernel threads, - * if only because they are not used by them anyway. - */ -#define CLONE_KERNEL (CLONE_FS | CLONE_FILES | CLONE_SIGHAND) - /* * These are the constant used to fake the fixed-point load-average * counting. Some notes: diff --git a/init/main.c b/init/main.c index 8ac3833f2bdf..4de815c0309a 100644 --- a/init/main.c +++ b/init/main.c @@ -380,7 +380,7 @@ static noinline void __init_refok rest_init(void) * 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); + kernel_thread(kernel_init, NULL, CLONE_FS); numa_default_policy(); pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES); rcu_read_lock();