Commit d9c82fd8 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'for-linus-2020-01-03' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux 

Pull thread fixes from Christian Brauner:
 "Here are two fixes:

   - Panic earlier when global init exits to generate useable coredumps.

     Currently, when global init and all threads in its thread-group
     have exited we panic via:

       do_exit()
       -> exit_notify()
          -> forget_original_parent()
             -> find_child_reaper()

     This makes it hard to extract a useable coredump for global init
     from a kernel crashdump because by the time we panic exit_mm() will
     have already released global init's mm. We now panic slightly
     earlier. This has been a problem in certain environments such as
     Android.

   - Fix a race in assigning and reading taskstats for thread-groups
     with more than one thread.

     This patch has been waiting for quite a while since people
     disagreed on what the correct fix was at first"

* tag 'for-linus-2020-01-03' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  exit: panic before exit_mm() on global init exit
  taskstats: fix data-race
parents 6f2e9c3d 43cf75d9

kernel/exit.c

+8 −4
Original line number Diff line number Diff line
@@ -517,10 +517,6 @@ static struct task_struct *find_child_reaper(struct task_struct *father, 
	}



	write_unlock_irq(&tasklist_lock);

	if (unlikely(pid_ns == &init_pid_ns)) {

		panic("Attempted to kill init! exitcode=0x%08x\n",

			father->signal->group_exit_code ?: father->exit_code);

	}



	list_for_each_entry_safe(p, n, dead, ptrace_entry) {

		list_del_init(&p->ptrace_entry);
@@ -766,6 +762,14 @@ void __noreturn do_exit(long code) 
	acct_update_integrals(tsk);

	group_dead = atomic_dec_and_test(&tsk->signal->live);

	if (group_dead) {

		/*

		 * If the last thread of global init has exited, panic

		 * immediately to get a useable coredump.

		 */

		if (unlikely(is_global_init(tsk)))

			panic("Attempted to kill init! exitcode=0x%08x\n",

				tsk->signal->group_exit_code ?: (int)code);



#ifdef CONFIG_POSIX_TIMERS

		hrtimer_cancel(&tsk->signal->real_timer);

		exit_itimers(tsk->signal);

kernel/taskstats.c

+19 −11
Original line number Diff line number Diff line
@@ -554,25 +554,33 @@ static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info) 
static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)

{

	struct signal_struct *sig = tsk->signal;

	struct taskstats *stats;

	struct taskstats *stats_new, *stats;



	if (sig->stats || thread_group_empty(tsk))

		goto ret;

	/* Pairs with smp_store_release() below. */

	stats = smp_load_acquire(&sig->stats);

	if (stats || thread_group_empty(tsk))

		return stats;



	/* No problem if kmem_cache_zalloc() fails */

	stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);

	stats_new = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);



	spin_lock_irq(&tsk->sighand->siglock);

	if (!sig->stats) {

		sig->stats = stats;

		stats = NULL;

	stats = sig->stats;

	if (!stats) {

		/*

		 * Pairs with smp_store_release() above and order the

		 * kmem_cache_zalloc().

		 */

		smp_store_release(&sig->stats, stats_new);

		stats = stats_new;

		stats_new = NULL;

	}

	spin_unlock_irq(&tsk->sighand->siglock);



	if (stats)

		kmem_cache_free(taskstats_cache, stats);

ret:

	return sig->stats;

	if (stats_new)

		kmem_cache_free(taskstats_cache, stats_new);



	return stats;

}



/* Send pid data out on exit */

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