From: Oleg Nesterov Currently kernel threads use sigprocmask(SIG_BLOCK) to protect against signals. This doesn't prevent the signal delivery, this only blocks signal_wake_up(). Every "killall -33 kthreadd" means a "struct siginfo" leak. Change kthreadd_setup() to set all handlers to SIG_IGN instead of blocking them (make a new helper ignore_signals() for that). If the kernel thread needs some signal, it should use allow_signal() anyway, and in that case it should not use CLONE_SIGHAND. Note that we can't change daemonize() (should die!) in the same way, because it can be used along with CLONE_SIGHAND. This means that allow_signal() still should unblock the signal to work correctly with daemonize()ed threads. However, disallow_signal() doesn't block the signal any longer but ignores it. NOTE: with or without this patch the kernel threads are not protected from handle_stop_signal(), this seems harmless, but not good. Signed-off-by: Oleg Nesterov Acked-by: "Eric W. Biederman" Signed-off-by: Andrew Morton --- include/linux/sched.h | 1 + kernel/exit.c | 2 +- kernel/kthread.c | 17 +++-------------- kernel/signal.c | 10 ++++++++++ 4 files changed, 15 insertions(+), 15 deletions(-) diff -puN include/linux/sched.h~change-kernel-threads-to-ignore-signals-instead-of-blocking-them include/linux/sched.h --- a/include/linux/sched.h~change-kernel-threads-to-ignore-signals-instead-of-blocking-them +++ a/include/linux/sched.h @@ -1302,6 +1302,7 @@ extern int in_egroup_p(gid_t); extern void proc_caches_init(void); extern void flush_signals(struct task_struct *); +extern void ignore_signals(struct task_struct *); extern void flush_signal_handlers(struct task_struct *, int force_default); extern int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info); diff -puN kernel/exit.c~change-kernel-threads-to-ignore-signals-instead-of-blocking-them kernel/exit.c --- a/kernel/exit.c~change-kernel-threads-to-ignore-signals-instead-of-blocking-them +++ a/kernel/exit.c @@ -350,7 +350,7 @@ int disallow_signal(int sig) return -EINVAL; spin_lock_irq(¤t->sighand->siglock); - sigaddset(¤t->blocked, sig); + current->sighand->action[(sig)-1].sa.sa_handler = SIG_IGN; recalc_sigpending(); spin_unlock_irq(¤t->sighand->siglock); return 0; diff -puN kernel/kthread.c~change-kernel-threads-to-ignore-signals-instead-of-blocking-them kernel/kthread.c --- a/kernel/kthread.c~change-kernel-threads-to-ignore-signals-instead-of-blocking-them +++ a/kernel/kthread.c @@ -215,24 +215,13 @@ EXPORT_SYMBOL(kthread_stop); static __init void kthreadd_setup(void) { struct task_struct *tsk = current; - struct k_sigaction sa; - sigset_t blocked; set_task_comm(tsk, "kthreadd"); - /* Block and flush all signals */ - sigfillset(&blocked); - sigprocmask(SIG_BLOCK, &blocked, NULL); - flush_signals(tsk); - - /* SIG_IGN makes children autoreap: see do_notify_parent(). */ - sa.sa.sa_handler = SIG_IGN; - sa.sa.sa_flags = 0; - siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD)); - do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0); + ignore_signals(tsk); - set_user_nice(current, -5); - set_cpus_allowed(current, CPU_MASK_ALL); + set_user_nice(tsk, -5); + set_cpus_allowed(tsk, CPU_MASK_ALL); } int kthreadd(void *unused) diff -puN kernel/signal.c~change-kernel-threads-to-ignore-signals-instead-of-blocking-them kernel/signal.c --- a/kernel/signal.c~change-kernel-threads-to-ignore-signals-instead-of-blocking-them +++ a/kernel/signal.c @@ -328,6 +328,16 @@ void flush_signals(struct task_struct *t spin_unlock_irqrestore(&t->sighand->siglock, flags); } +void ignore_signals(struct task_struct *t) +{ + int i; + + for (i = 0; i < _NSIG; ++i) + t->sighand->action[i].sa.sa_handler = SIG_IGN; + + flush_signals(t); +} + /* * Flush all handlers for a task. */ _