[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>

1 files changed, 2 insertions, 3 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 8e88b374cee9..3683ce10f4a9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1123,8 +1123,8 @@ static task_t *copy_process(unsigned long clone_flags,
                 p->real_parent = current;
         p->parent = p->real_parent;
 
+        spin_lock(&current->sighand->siglock);
         if (clone_flags & CLONE_THREAD) {
-                spin_lock(&current->sighand->siglock);
                 /*
                  * 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;