[PATCH] sys_setpgid: eliminate unnecessary do_each_task_pid(PIDTYPE_PGID)

All tasks in the process group have the same sid, we don't need to iterate
them all to check that the caller of sys_setpgid() doesn't change its
session.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 4 insertions, 7 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index 4f9d23a3095f..c7675c1bfdf2 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1397,16 +1397,13 @@ asmlinkage long sys_setpgid(pid_t pid, pid_t pgid)
                 goto out;
 
         if (pgid != pid) {
-                struct task_struct *p;
+                struct task_struct *g =
+                        find_task_by_pid_type(PIDTYPE_PGID, pgid);
 
-                do_each_task_pid(pgid, PIDTYPE_PGID, p) {
-                        if (process_session(p) == process_session(group_leader))
-                                goto ok_pgid;
-                } while_each_task_pid(pgid, PIDTYPE_PGID, p);
-                goto out;
+                if (!g || process_session(g) != process_session(group_leader))
+                        goto out;
         }
 
-ok_pgid:
         err = security_task_setpgid(p, pgid);
         if (err)
                 goto out;