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>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20091209100706.753790977@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index 258c73c6a2f3adecdf03933706fc1b7d4a364ce5..1782beed2fa75eed098fbdaf60650ed5ca91200f 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6458,7 +6458,7 @@ SYSCALL_DEFINE1(sched_getscheduler, pid_t, 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);
@@ -6466,7 +6466,7 @@ SYSCALL_DEFINE1(sched_getscheduler, pid_t, pid)
                        retval = p->policy
                                | (p->sched_reset_on_fork ? SCHED_RESET_ON_FORK : 0);
        }
-       read_unlock(&tasklist_lock);
+       rcu_read_unlock();
        return retval;
 }
 
@@ -6484,7 +6484,7 @@ SYSCALL_DEFINE2(sched_getparam, pid_t, pid, struct sched_param __user *, param)
        if (!param || pid < 0)
                return -EINVAL;
 
-       read_lock(&tasklist_lock);
+       rcu_read_lock();
        p = find_process_by_pid(pid);
        retval = -ESRCH;
        if (!p)
@@ -6495,7 +6495,7 @@ SYSCALL_DEFINE2(sched_getparam, pid_t, pid, struct sched_param __user *, param)
                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 ...
@@ -6505,7 +6505,7 @@ SYSCALL_DEFINE2(sched_getparam, pid_t, pid, struct sched_param __user *, param)
        return retval;
 
 out_unlock:
-       read_unlock(&tasklist_lock);
+       rcu_read_unlock();
        return retval;
 }