[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20100603183040.GA2385@linux.vnet.ibm.com>
Date: Thu, 3 Jun 2010 11:30:40 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Li Zefan <lizf@...fujitsu.com>
Cc: Daniel J Blueman <daniel.blueman@...il.com>,
Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] RCU: don't turn off lockdep when find suspicious
rcu_dereference_check() usage
On Thu, Jun 03, 2010 at 05:22:04PM +0800, Li Zefan wrote:
> Paul E. McKenney wrote:
> > On Tue, Jun 01, 2010 at 02:06:13PM +0100, Daniel J Blueman wrote:
> >> Hi Paul,
> >>
> >> With 2.6.35-rc1 and your patch in the context below, we still see
> >> "include/linux/cgroup.h:534 invoked rcu_dereference_check() without
> >> protection!", so need this additional patch:
> >>
> >> Acquire read-side RCU lock around task_group() calls, addressing
> >> "include/linux/cgroup.h:534 invoked rcu_dereference_check() without
> >> protection!" warning.
> >>
> >> Signed-off-by: Daniel J Blueman <daniel.blueman@...il.com>
> >
> > Thank you, Daniel! I have queued this for 2.6.35.
> >
> > I had to apply the patch by hand due to line wrapping. Could you please
> > check your email-agent settings? This simple patch was no problem to
> > hand apply, but for a larger patch this process would be both tedious
> > and error prone.
> >
> > Thanx, Paul
> >
> >> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> >> index 217e4a9..50ec9ea 100644
> >> --- a/kernel/sched_fair.c
> >> +++ b/kernel/sched_fair.c
> >> @@ -1241,6 +1241,7 @@ static int wake_affine(struct sched_domain *sd,
> >> struct task_struct *p, int sync)
> >> * effect of the currently running task from the load
> >> * of the current CPU:
> >> */
> >> + rcu_read_lock();
> >> if (sync) {
> >> tg = task_group(current);
> >> weight = current->se.load.weight;
> >> @@ -1250,6 +1251,7 @@ static int wake_affine(struct sched_domain *sd,
> >> struct task_struct *p, int sync)
> >> }
> >>
> >> tg = task_group(p);
> >> + rcu_read_unlock();
>
> Hmmm.. I think it's not safe to access tg after rcu_read_unlock.
It does indeed look unsafe. How about the following on top of this patch?
> >> weight = p->se.load.weight;
> >>
> >> imbalance = 100 + (sd->imbalance_pct - 100) / 2;
Seems worth reviewing the other uses of task_group():
1. set_task_rq() -- only a runqueue and a sched_rt_entity leave
the RCU read-side critical section. Runqueues do persist.
I don't claim to understand the sched_rt_entity life cycle.
2. __sched_setscheduler() -- not clear to me that this one is
protected to begin with. If it is somehow correctly protected,
it discards the RCU-protected pointer immediately, so is OK
otherwise.
3. cpu_cgroup_destroy() -- ditto.
4. cpu_shares_read_u64() -- ditto.
5. print_task() -- protected by rcu_read_lock() and discards the
RCU-protected pointer immediately, so this one is OK.
Any task_group() experts able to weigh in on #2, #3, and #4?
Thanx, Paul
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 50ec9ea..224ef98 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1251,7 +1251,6 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
}
tg = task_group(p);
- rcu_read_unlock();
weight = p->se.load.weight;
imbalance = 100 + (sd->imbalance_pct - 100) / 2;
@@ -1268,6 +1267,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
balanced = !this_load ||
100*(this_load + effective_load(tg, this_cpu, weight, weight)) <=
imbalance*(load + effective_load(tg, prev_cpu, 0, weight));
+ rcu_read_unlock();
/*
* If the currently running task will sleep within
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists