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Commit 5fe85be0 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Ingo Molnar
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20091209100706.753790977@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 663997d4

kernel/sched.c

+5 −5
Original line number Diff line number Diff line
@@ -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;

}