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Commit d68b46fe authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

vfork: make it killable 



Make vfork() killable.

Change do_fork(CLONE_VFORK) to do wait_for_completion_killable().  If it
fails we do not return to the user-mode and never touch the memory shared
with our child.

However, in this case we should clear child->vfork_done before return, we
use task_lock() in do_fork()->wait_for_vfork_done() and
complete_vfork_done() to serialize with each other.

Note: now that we use task_lock() we don't really need completion, we
could turn task->vfork_done into "task_struct *wake_up_me" but this needs
some complications.

NOTE: this and the next patches do not affect in-kernel users of
CLONE_VFORK, kernel threads run with all signals ignored including
SIGKILL/SIGSTOP.

However this is obviously the user-visible change.  Not only a fatal
signal can kill the vforking parent, a sub-thread can do execve or
exit_group() and kill the thread sleeping in vfork().

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c415c3b4

include/linux/sched.h

+1 −1
Original line number Diff line number Diff line
@@ -2372,7 +2372,7 @@ static inline int thread_group_empty(struct task_struct *p) 
 * Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring

 * subscriptions and synchronises with wait4().  Also used in procfs.  Also

 * pins the final release of task.io_context.  Also protects ->cpuset and

 * ->cgroup.subsys[].

 * ->cgroup.subsys[]. And ->vfork_done.

 *

 * Nests both inside and outside of read_lock(&tasklist_lock).

 * It must not be nested with write_lock_irq(&tasklist_lock),

kernel/fork.c

+32 −8
Original line number Diff line number Diff line
@@ -670,10 +670,34 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode) 


void complete_vfork_done(struct task_struct *tsk)

{

	struct completion *vfork_done = tsk->vfork_done;

	struct completion *vfork;



	task_lock(tsk);

	vfork = tsk->vfork_done;

	if (likely(vfork)) {

		tsk->vfork_done = NULL;

	complete(vfork_done);

		complete(vfork);

	}

	task_unlock(tsk);

}



static int wait_for_vfork_done(struct task_struct *child,

				struct completion *vfork)

{

	int killed;



	freezer_do_not_count();

	killed = wait_for_completion_killable(vfork);

	freezer_count();



	if (killed) {

		task_lock(child);

		child->vfork_done = NULL;

		task_unlock(child);

	}



	put_task_struct(child);

	return killed;

}



/* Please note the differences between mmput and mm_release.
@@ -717,7 +741,8 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm) 
	 * If we're exiting normally, clear a user-space tid field if

	 * requested.  We leave this alone when dying by signal, to leave

	 * the value intact in a core dump, and to save the unnecessary

	 * trouble otherwise.  Userland only wants this done for a sys_exit.

	 * trouble, say, a killed vfork parent shouldn't touch this mm.

	 * Userland only wants this done for a sys_exit.

	 */

	if (tsk->clear_child_tid) {

		if (!(tsk->flags & PF_SIGNALED) &&
@@ -1551,6 +1576,7 @@ long do_fork(unsigned long clone_flags, 
		if (clone_flags & CLONE_VFORK) {

			p->vfork_done = &vfork;

			init_completion(&vfork);

			get_task_struct(p);

		}



		/*
@@ -1568,9 +1594,7 @@ long do_fork(unsigned long clone_flags, 
			ptrace_event(trace, nr);



		if (clone_flags & CLONE_VFORK) {

			freezer_do_not_count();

			wait_for_completion(&vfork);

			freezer_count();

			if (!wait_for_vfork_done(p, &vfork))

				ptrace_event(PTRACE_EVENT_VFORK_DONE, nr);

		}

	} else {