Commit a7f0765e authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

ptrace: __ptrace_detach: do __wake_up_parent() if we reap the tracee



The bug is old, it wasn't cause by recent changes.

Test case:

	static void *tfunc(void *arg)
	{
		int pid = (long)arg;

		assert(ptrace(PTRACE_ATTACH, pid, NULL, NULL) == 0);
		kill(pid, SIGKILL);

		sleep(1);
		return NULL;
	}

	int main(void)
	{
		pthread_t th;
		long pid = fork();

		if (!pid)
			pause();

		signal(SIGCHLD, SIG_IGN);
		assert(pthread_create(&th, NULL, tfunc, (void*)pid) == 0);

		int r = waitpid(-1, NULL, __WNOTHREAD);
		printf("waitpid: %d %m\n", r);

		return 0;
	}

Before the patch this program hangs, after this patch waitpid() correctly
fails with errno == -ECHILD.

The problem is, __ptrace_detach() reaps the EXIT_ZOMBIE tracee if its
->real_parent is our sub-thread and we ignore SIGCHLD.  But in this case
we should wake up other threads which can sleep in do_wait().
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Vitaly Mayatskikh <vmayatsk@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1dd3a273
......@@ -2059,6 +2059,7 @@ extern int kill_pgrp(struct pid *pid, int sig, int priv);
extern int kill_pid(struct pid *pid, int sig, int priv);
extern int kill_proc_info(int, struct siginfo *, pid_t);
extern int do_notify_parent(struct task_struct *, int);
extern void __wake_up_parent(struct task_struct *p, struct task_struct *parent);
extern void force_sig(int, struct task_struct *);
extern void force_sig_specific(int, struct task_struct *);
extern int send_sig(int, struct task_struct *, int);
......
......@@ -1575,6 +1575,11 @@ static int ptrace_do_wait(struct wait_opts *wo, struct task_struct *tsk)
return 0;
}
void __wake_up_parent(struct task_struct *p, struct task_struct *parent)
{
wake_up_interruptible_sync(&parent->signal->wait_chldexit);
}
static long do_wait(struct wait_opts *wo)
{
DECLARE_WAITQUEUE(wait, current);
......
......@@ -266,9 +266,10 @@ static int ignoring_children(struct sighand_struct *sigh)
* or self-reaping. Do notification now if it would have happened earlier.
* If it should reap itself, return true.
*
* If it's our own child, there is no notification to do.
* But if our normal children self-reap, then this child
* was prevented by ptrace and we must reap it now.
* If it's our own child, there is no notification to do. But if our normal
* children self-reap, then this child was prevented by ptrace and we must
* reap it now, in that case we must also wake up sub-threads sleeping in
* do_wait().
*/
static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p)
{
......@@ -278,8 +279,10 @@ static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p)
if (!task_detached(p) && thread_group_empty(p)) {
if (!same_thread_group(p->real_parent, tracer))
do_notify_parent(p, p->exit_signal);
else if (ignoring_children(tracer->sighand))
else if (ignoring_children(tracer->sighand)) {
__wake_up_parent(p, tracer);
p->exit_signal = -1;
}
}
if (task_detached(p)) {
/* Mark it as in the process of being reaped. */
......
......@@ -1382,15 +1382,6 @@ int send_sigqueue(struct sigqueue *q, struct task_struct *t, int group)
return ret;
}
/*
* Wake up any threads in the parent blocked in wait* syscalls.
*/
static inline void __wake_up_parent(struct task_struct *p,
struct task_struct *parent)
{
wake_up_interruptible_sync(&parent->signal->wait_chldexit);
}
/*
* Let a parent know about the death of a child.
* For a stopped/continued status change, use do_notify_parent_cldstop instead.
......
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment