Commit 3f17da69 authored Feb 15, 2006 by Oleg Nesterov Committed by Linus Torvalds Feb 15, 2006

[PATCH] fix kill_proc_info() vs CLONE_THREAD race



There is a window after copy_process() unlocks ->sighand.siglock
and before it adds the new thread to the thread list.

In that window __group_complete_signal(SIGKILL) will not see the
new thread yet, so this thread will start running while the whole
thread group was supposed to exit.

I beleive we have another good reason to place attach_pid(PID/TGID)
under ->sighand.siglock. We can do the same for

	release_task()->__unhash_process()

	de_thread()->switch_exec_pids()

After that we don't need tasklist_lock to iterate over the thread
list, and we can simplify things, see for example do_sigaction()
or sys_times().

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 7775aa76

kernel/fork.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -1123,8 +1123,8 @@ static task_t *copy_process(unsigned long clone_flags,
		p->real_parent = current;
		p->parent = p->real_parent;

		if (clone_flags & CLONE_THREAD) {
		spin_lock(&current->sighand->siglock);
		if (clone_flags & CLONE_THREAD) {
		/*
		* Important: if an exit-all has been started then
		* do not create this new thread - the whole thread
		@@ -1162,8 +1162,6 @@ static task_t *copy_process(unsigned long clone_flags,
		*/
		p->it_prof_expires = jiffies_to_cputime(1);
		}

		spin_unlock(&current->sighand->siglock);
		}

		/*
		@@ -1189,6 +1187,7 @@ static task_t *copy_process(unsigned long clone_flags,

		nr_threads++;
		total_forks++;
		spin_unlock(&current->sighand->siglock);
		write_unlock_irq(&tasklist_lock);
		proc_fork_connector(p);
		return p;

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