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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>
This commit is contained in:
Thomas Gleixner 2009-12-09 10:14:58 +00:00 committed by Ingo Molnar
parent 663997d417
commit 5fe85be081
1 changed files with 5 additions and 5 deletions
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10
kernel/sched.c
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@ -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;
}