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Subject[PATCH 2/4] 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>

--- 2.6.18-rc4/kernel/sched.c~2_signal 2006-08-19 20:22:09.000000000 +0400
+++ 2.6.18-rc4/kernel/sched.c 2006-08-19 21:14:19.000000000 +0400
@@ -4043,6 +4043,8 @@ static void __setscheduler(struct task_s
* @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)
@@ -4078,19 +4080,26 @@ 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) &&
@@ -4156,14 +4165,13 @@ do_sched_setscheduler(pid_t pid, int pol
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;
}
-
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