Commit d9c82fd8 authored by Linus Torvalds's avatar Linus Torvalds

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
...@@ -517,10 +517,6 @@ static struct task_struct *find_child_reaper(struct task_struct *father, ...@@ -517,10 +517,6 @@ static struct task_struct *find_child_reaper(struct task_struct *father,
} }
write_unlock_irq(&tasklist_lock); 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_for_each_entry_safe(p, n, dead, ptrace_entry) {
list_del_init(&p->ptrace_entry); list_del_init(&p->ptrace_entry);
...@@ -766,6 +762,14 @@ void __noreturn do_exit(long code) ...@@ -766,6 +762,14 @@ void __noreturn do_exit(long code)
acct_update_integrals(tsk); acct_update_integrals(tsk);
group_dead = atomic_dec_and_test(&tsk->signal->live); group_dead = atomic_dec_and_test(&tsk->signal->live);
if (group_dead) { 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 #ifdef CONFIG_POSIX_TIMERS
hrtimer_cancel(&tsk->signal->real_timer); hrtimer_cancel(&tsk->signal->real_timer);
exit_itimers(tsk->signal); exit_itimers(tsk->signal);
......
...@@ -554,25 +554,33 @@ static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info) ...@@ -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) static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)
{ {
struct signal_struct *sig = tsk->signal; struct signal_struct *sig = tsk->signal;
struct taskstats *stats; struct taskstats *stats_new, *stats;
if (sig->stats || thread_group_empty(tsk)) /* Pairs with smp_store_release() below. */
goto ret; stats = smp_load_acquire(&sig->stats);
if (stats || thread_group_empty(tsk))
return stats;
/* No problem if kmem_cache_zalloc() fails */ /* 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); spin_lock_irq(&tsk->sighand->siglock);
if (!sig->stats) { stats = sig->stats;
sig->stats = stats; if (!stats) {
stats = NULL; /*
* 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); spin_unlock_irq(&tsk->sighand->siglock);
if (stats) if (stats_new)
kmem_cache_free(taskstats_cache, stats); kmem_cache_free(taskstats_cache, stats_new);
ret:
return sig->stats; return stats;
} }
/* Send pid data out on exit */ /* Send pid data out on exit */
......
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