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Subject[patch 1/4] sched: Use rcu in sys_sched_getscheduler/sys_sched_getparam()
read_lock(&tasklist_lock) does not protect sys_sched_getscheduler and
sys_sched_getparam() against a concurrent update of the policy or
scheduler parameters as do_sched_setscheduler() does not take the
tasklist_lock. The accessed integers can be retrieved w/o locking and
are snapshots anyway.

Using rcu_read_lock() to protect find_task_by_vpid() and prevent the
task struct from going away is not changing the above situation.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/sched.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

Index: linux-2.6-tip/kernel/sched.c
===================================================================
--- linux-2.6-tip.orig/kernel/sched.c
+++ linux-2.6-tip/kernel/sched.c
@@ -6477,7 +6477,7 @@ SYSCALL_DEFINE1(sched_getscheduler, pid_
return -EINVAL;

retval = -ESRCH;
- read_lock(&tasklist_lock);
+ rcu_read_lock();
p = find_process_by_pid(pid);
if (p) {
retval = security_task_getscheduler(p);
@@ -6485,7 +6485,7 @@ SYSCALL_DEFINE1(sched_getscheduler, pid_
retval = p->policy
| (p->sched_reset_on_fork ? SCHED_RESET_ON_FORK : 0);
}
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
return retval;
}

@@ -6503,7 +6503,7 @@ SYSCALL_DEFINE2(sched_getparam, pid_t, p
if (!param || pid < 0)
return -EINVAL;

- read_lock(&tasklist_lock);
+ rcu_read_lock();
p = find_process_by_pid(pid);
retval = -ESRCH;
if (!p)
@@ -6514,7 +6514,7 @@ SYSCALL_DEFINE2(sched_getparam, pid_t, p
goto out_unlock;

lp.sched_priority = p->rt_priority;
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();

/*
* This one might sleep, we cannot do it with a spinlock held ...
@@ -6524,7 +6524,7 @@ SYSCALL_DEFINE2(sched_getparam, pid_t, p
return retval;

out_unlock:
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
return retval;
}




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