[PATCH] do_sched_setscheduler(): don't take tasklist_lock

Use rcu locks instead. sched_setscheduler() now takes ->siglock
before reading ->signal->rlim[].

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 18 insertions, 10 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index b946209d9c15..f9b3c6a414f1 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4080,6 +4080,8 @@ static void __setscheduler(struct task_struct *p, int policy, int prio)
  * @p: the task in question.
  * @policy: new policy.
  * @param: structure containing the new RT priority.
+ *
+ * NOTE: the task may be already dead
  */
 int sched_setscheduler(struct task_struct *p, int policy,
                        struct sched_param *param)
@@ -4115,19 +4117,26 @@ recheck:
          * Allow unprivileged RT tasks to decrease priority:
          */
         if (!capable(CAP_SYS_NICE)) {
+                unsigned long rlim_rtprio;
+                unsigned long flags;
+
+                if (!lock_task_sighand(p, &flags))
+                        return -ESRCH;
+                rlim_rtprio = p->signal->rlim[RLIMIT_RTPRIO].rlim_cur;
+                unlock_task_sighand(p, &flags);
+
                 /*
                  * can't change policy, except between SCHED_NORMAL
                  * and SCHED_BATCH:
                  */
                 if (((policy != SCHED_NORMAL && p->policy != SCHED_BATCH) &&
                         (policy != SCHED_BATCH && p->policy != SCHED_NORMAL)) &&
-                                !p->signal->rlim[RLIMIT_RTPRIO].rlim_cur)
+                                !rlim_rtprio)
                         return -EPERM;
                 /* can't increase priority */
                 if ((policy != SCHED_NORMAL && policy != SCHED_BATCH) &&
                     param->sched_priority > p->rt_priority &&
-                    param->sched_priority >
-                                p->signal->rlim[RLIMIT_RTPRIO].rlim_cur)
+                    param->sched_priority > rlim_rtprio)
                         return -EPERM;
                 /* can't change other user's priorities */
                 if ((current->euid != p->euid) &&
@@ -4193,14 +4202,13 @@ do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param)
                 return -EINVAL;
         if (copy_from_user(&lparam, param, sizeof(struct sched_param)))
                 return -EFAULT;
-        read_lock_irq(&tasklist_lock);
+
+        rcu_read_lock();
+        retval = -ESRCH;
         p = find_process_by_pid(pid);
-        if (!p) {
-                read_unlock_irq(&tasklist_lock);
-                return -ESRCH;
-        }
-        retval = sched_setscheduler(p, policy, &lparam);
-        read_unlock_irq(&tasklist_lock);
+        if (p != NULL)
+                retval = sched_setscheduler(p, policy, &lparam);
+        rcu_read_unlock();
 
         return retval;
 }