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kthread: Ensure struct kthread is present for all kthreads
Today the rules are a bit iffy and arbitrary about which kernel threads have struct kthread present. Both idle threads and thread started with create_kthread want struct kthread present so that is effectively all kernel threads. Make the rule that if PF_KTHREAD and the task is running then struct kthread is present. This will allow the kernel thread code to using tsk->exit_code with different semantics from ordinary processes. To make ensure that struct kthread is present for all kernel threads move it's allocation into copy_process. Add a deallocation of struct kthread in exec for processes that were kernel threads. Move the allocation of struct kthread for the initial thread earlier so that it is not repeated for each additional idle thread. Move the initialization of struct kthread into set_kthread_struct so that the structure is always and reliably initailized. Clear set_child_tid in free_kthread_struct to ensure the kthread struct is reliably freed during exec. The function free_kthread_struct does not need to clear vfork_done during exec as exec_mm_release called from exec_mmap has already cleared vfork_done. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
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40966e316f
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@ -1307,6 +1307,8 @@ int begin_new_exec(struct linux_binprm * bprm)
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*/
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force_uaccess_begin();
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if (me->flags & PF_KTHREAD)
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free_kthread_struct(me);
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me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
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PF_NOFREEZE | PF_NO_SETAFFINITY);
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flush_thread();
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@ -33,7 +33,7 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
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unsigned int cpu,
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const char *namefmt);
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void set_kthread_struct(struct task_struct *p);
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bool set_kthread_struct(struct task_struct *p);
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void kthread_set_per_cpu(struct task_struct *k, int cpu);
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bool kthread_is_per_cpu(struct task_struct *k);
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@ -2118,6 +2118,10 @@ static __latent_entropy struct task_struct *copy_process(
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p->io_context = NULL;
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audit_set_context(p, NULL);
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cgroup_fork(p);
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if (p->flags & PF_KTHREAD) {
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if (!set_kthread_struct(p))
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goto bad_fork_cleanup_threadgroup_lock;
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}
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#ifdef CONFIG_NUMA
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p->mempolicy = mpol_dup(p->mempolicy);
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if (IS_ERR(p->mempolicy)) {
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@ -93,20 +93,27 @@ static inline struct kthread *__to_kthread(struct task_struct *p)
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return kthread;
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}
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void set_kthread_struct(struct task_struct *p)
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bool set_kthread_struct(struct task_struct *p)
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{
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struct kthread *kthread;
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if (__to_kthread(p))
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return;
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if (WARN_ON_ONCE(to_kthread(p)))
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return false;
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kthread = kzalloc(sizeof(*kthread), GFP_KERNEL);
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if (!kthread)
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return false;
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init_completion(&kthread->exited);
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init_completion(&kthread->parked);
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p->vfork_done = &kthread->exited;
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/*
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* We abuse ->set_child_tid to avoid the new member and because it
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* can't be wrongly copied by copy_process(). We also rely on fact
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* that the caller can't exec, so PF_KTHREAD can't be cleared.
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* can't be wrongly copied by copy_process().
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*/
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p->set_child_tid = (__force void __user *)kthread;
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return true;
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}
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void free_kthread_struct(struct task_struct *k)
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@ -114,13 +121,13 @@ void free_kthread_struct(struct task_struct *k)
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struct kthread *kthread;
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/*
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* Can be NULL if this kthread was created by kernel_thread()
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* or if kmalloc() in kthread() failed.
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* Can be NULL if kmalloc() in set_kthread_struct() failed.
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*/
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kthread = to_kthread(k);
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#ifdef CONFIG_BLK_CGROUP
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WARN_ON_ONCE(kthread && kthread->blkcg_css);
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#endif
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k->set_child_tid = (__force void __user *)NULL;
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kfree(kthread);
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}
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@ -315,7 +322,6 @@ static int kthread(void *_create)
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struct kthread *self;
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int ret;
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set_kthread_struct(current);
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self = to_kthread(current);
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/* If user was SIGKILLed, I release the structure. */
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@ -325,17 +331,8 @@ static int kthread(void *_create)
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kthread_exit(-EINTR);
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}
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if (!self) {
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create->result = ERR_PTR(-ENOMEM);
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complete(done);
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kthread_exit(-ENOMEM);
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}
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self->threadfn = threadfn;
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self->data = data;
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init_completion(&self->exited);
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init_completion(&self->parked);
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current->vfork_done = &self->exited;
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/*
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* The new thread inherited kthreadd's priority and CPU mask. Reset
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@ -8599,14 +8599,6 @@ void __init init_idle(struct task_struct *idle, int cpu)
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__sched_fork(0, idle);
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/*
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* The idle task doesn't need the kthread struct to function, but it
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* is dressed up as a per-CPU kthread and thus needs to play the part
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* if we want to avoid special-casing it in code that deals with per-CPU
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* kthreads.
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*/
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set_kthread_struct(idle);
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raw_spin_lock_irqsave(&idle->pi_lock, flags);
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raw_spin_rq_lock(rq);
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@ -9427,6 +9419,14 @@ void __init sched_init(void)
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mmgrab(&init_mm);
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enter_lazy_tlb(&init_mm, current);
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/*
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* The idle task doesn't need the kthread struct to function, but it
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* is dressed up as a per-CPU kthread and thus needs to play the part
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* if we want to avoid special-casing it in code that deals with per-CPU
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* kthreads.
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*/
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WARN_ON(set_kthread_struct(current));
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/*
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* Make us the idle thread. Technically, schedule() should not be
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* called from this thread, however somewhere below it might be,
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