Oleg Nesterov wrote:
> Yes, yes, and I already tried to comment this part. We probably need a
> dedicated kernel thread, but I still think (although I am not sure) that
> initial change can use workueue. In the likely case system_unbound_wq pool
> should have an idle thread, if not - OK, this change won't help in this
> case. This is minor.
>
I imagined a dedicated kernel thread doing something like shown below.
(I don't know about mm->mmap management.)
mm->mmap_zapped corresponds to MMF_MEMDIE.
I think this kernel thread can be used for normal kill(pid, SIGKILL) cases.
----------
bool has_sigkill_task;
wait_queue_head_t kick_mm_zapper;
static void mm_zapper(void *unused)
{
struct task_struct *g, *p;
struct mm_struct *mm;
sleep:
wait_event(kick_remover, has_sigkill_task);
has_sigkill_task = false;
restart:
rcu_read_lock();
for_each_process_thread(g, p) {
if (likely(!fatal_signal_pending(p)))
continue;
task_lock(p);
mm = p->mm;
if (mm && mm->mmap && !mm->mmap_zapped && down_read_trylock(&mm->mmap_sem)) {
atomic_inc(&mm->mm_users);
task_unlock(p);
rcu_read_unlock();
if (mm->mmap && !mm->mmap_zapped)
zap_page_range(mm->mmap, 0, TASK_SIZE, NULL);
mm->mmap_zapped = 1;
up_read(&mm->mmap_sem);
mmput(mm);
cond_resched();
goto restart;
}
task_unlock(p);
}
rcu_read_unlock();
goto sleep;
}
kthread_run(mm_zapper, NULL, "mm_zapper");
----------
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