uglify while_each_pid_task() to make sure we don't count the execing pricess twice

There is a window when de_thread() switches the leader and drops
tasklist_lock.  In that window do_each_pid_task(PIDTYPE_PID) finds both new
and old leaders.

The problem is pretty much theoretical and probably can be ignored.  Currently
the only users of do_each_pid_task(PIDTYPE_PID) are send_sigio/send_sigurg, so
they can send the signal to the same process twice.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/pid.h b/include/linux/pid.h
index b91f473..f84d532 100644 (file)
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -152,7 +152,13 @@ pid_t pid_vnr(struct pid *pid);
                        hlist_for_each_entry_rcu((task), pos___,        \
                                &pid->tasks[type], pids[type].node) {
 
+                       /*
+                        * Both old and new leaders may be attached to
+                        * the same pid in the middle of de_thread().
+                        */
 #define while_each_pid_task(pid, type, task)                           \
+                               if (type == PIDTYPE_PID)                \
+                                       break;                          \
                        }                                               \
        } while (0)