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Subject[073/123] sched: Use rcu in sys_sched_getscheduler/sys_sched_getparam()
From: Thomas Gleixner <tglx@linutronix.de>

commit 5fe85be081edf0ac92d83f9c39e0ab5c1371eb82 upstream

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>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
kernel/sched.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6505,7 +6505,7 @@ 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);
@@ -6513,7 +6513,7 @@ 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;
}

@@ -6531,7 +6531,7 @@ 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)
@@ -6542,7 +6542,7 @@ 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 ...
@@ -6552,7 +6552,7 @@ SYSCALL_DEFINE2(sched_getparam, pid_t, p
return retval;

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




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