[PATCH] cpuset: current_cpuset_is_being_rebound() need rcu lock
KOSAKI Motohiro
the fixing is trivial. but I wonder why don't cpuset_being_rebound assignment
and read need a memory barrier pairing?
=============== CUT HERE ==========================================
Subject: [PATCH] cpuset: current_cpuset_is_being_rebound() need rcu lock.
Currently, rcu-lockdep display following warning.
because current_cpuset_is_being_rebound() call task_cs(), but it isn't
protected by rcu lock.
This patch fixes it.
===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
include/linux/cgroup.h:534 invoked rcu_dereference_check() without
protection!
other info that might help us debug this:
no locks held by swapper/0.
stack backtrace:
Pid: 0, comm: swapper Not tainted 2.6.34-rc1-mm1+ #94
Call Trace:
[<ffffffff81086961>] lockdep_rcu_dereference+0xa1/0xb0
[<ffffffff810a8cba>] current_cpuset_is_being_rebound+0x7a/0x80
[<ffffffff8112ae0a>] __mpol_dup+0x3a/0xa0
[<ffffffff8143b9e9>] ? sub_preempt_count+0x9/0xa0
[<ffffffff81438105>] ? _raw_spin_unlock+0x35/0x60
[<ffffffff810a29dd>] ? cgroup_fork+0x4d/0x70
[<ffffffff8104d1b0>] copy_process+0x530/0x1360
[<ffffffff8104e067>] do_fork+0x87/0x470
[<ffffffff8100a8a7>] ? native_sched_clock+0x27/0x80
[<ffffffff81078adf>] ? cpu_clock+0x4f/0x60
[<ffffffff81435b2e>] ? mutex_unlock+0xe/0x10
[<ffffffff81084c09>] ? trace_hardirqs_off_caller+0x29/0xe0
[<ffffffff8143b9e9>] ? sub_preempt_count+0x9/0xa0
[<ffffffff8108579e>] ? put_lock_stats+0xe/0x30
[<ffffffff8100b5c1>] kernel_thread+0x71/0x80
[<ffffffff81b465b3>] ? kernel_init+0x0/0x253
[<ffffffff81003f10>] ? kernel_thread_helper+0x0/0x10
[<ffffffff8106ea24>] ? rcu_scheduler_starting+0x24/0x60
[<ffffffff8141c6a6>] rest_init+0x26/0x110
[<ffffffff81b46dea>] start_kernel+0x3b9/0x3c5
[<ffffffff81b46310>] x86_64_start_reservations+0x120/0x124
[<ffffffff81b463f8>] x86_64_start_kernel+0xe4/0xeb
Signed-off-by: KOSAKI Motohiro <kosaki....@jp.fujitsu.com>
Cc: Miao Xie <mi...@cn.fujitsu.com>
Cc: Paul Menage <men...@google.com>
Cc: David Rientjes <rien...@google.com>
Cc: Li Zefan <li...@cn.fujitsu.com>
Cc: Nick Piggin <npi...@suse.de>
---
kernel/cpuset.c | 9 ++++++++-
1 files changed, 8 insertions(+), 1 deletions(-)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index b15c01c..4d44f76 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1129,7 +1129,14 @@ done:
int current_cpuset_is_being_rebound(void)
{
- return task_cs(current) == cpuset_being_rebound;
+ int being_rebound = 0;
+
+ rcu_read_lock();
+ if (task_cs(current) == cpuset_being_rebound)
+ being_rebound = 1;
+ rcu_read_unlock();
+
+ return being_rebound;
}
static int update_relax_domain_level(struct cpuset *cs, s64 val)
--
1.6.5.2
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Paul E. McKenney
> rcu lockdep detected cpuset have wrong rcu usage.
> the fixing is trivial. but I wonder why don't cpuset_being_rebound assignment
> and read need a memory barrier pairing?
The fix is in -tip, commit 99ee4ca746dda71326db7645463b4075ac1d665c.
This is an initialization-time use of rcu_dereference(), so no other
task has a reference to this data. Hence it is constant. Other uses
of this code operate on shared data structures, which might change at
any time.
Thanx, Paul
KOSAKI Motohiro
> > rcu lockdep detected cpuset have wrong rcu usage.
> > the fixing is trivial. but I wonder why don't cpuset_being_rebound assignment
> > and read need a memory barrier pairing?
>
> The fix is in -tip, commit 99ee4ca746dda71326db7645463b4075ac1d665c.
>
> This is an initialization-time use of rcu_dereference(), so no other
> task has a reference to this data. Hence it is constant. Other uses
> of this code operate on shared data structures, which might change at
> any time.
thanks. I haven't notice such commit.
I think you are talking about task_cs(current) accessing and you are right
in such point.
but I'm talking cpuset_being_rebound global variable.
update_tasks_nodemask() has following code
static void update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem,
struct ptr_heap *heap)
{
cpuset_being_rebound = cs; /* start transaction */
cgroup_scan_tasks(&scan);
cpuset_being_rebound = NULL; /* end transaction */
Paul E. McKenney
> > On Thu, Mar 11, 2010 at 02:46:15PM +0900, KOSAKI Motohiro wrote:
> > > rcu lockdep detected cpuset have wrong rcu usage.
> > > the fixing is trivial. but I wonder why don't cpuset_being_rebound assignment
> > > and read need a memory barrier pairing?
> >
> > The fix is in -tip, commit 99ee4ca746dda71326db7645463b4075ac1d665c.
> >
> > This is an initialization-time use of rcu_dereference(), so no other
> > task has a reference to this data. Hence it is constant. Other uses
> > of this code operate on shared data structures, which might change at
> > any time.
>
> thanks. I haven't notice such commit.
>
> I think you are talking about task_cs(current) accessing and you are right
> in such point.
> but I'm talking cpuset_being_rebound global variable.
>
> update_tasks_nodemask() has following code
>
> static void update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem,
> struct ptr_heap *heap)
> {
> cpuset_being_rebound = cs; /* start transaction */
> cgroup_scan_tasks(&scan);
> cpuset_being_rebound = NULL; /* end transaction */
> }
Hmmm... What commit are you looking at in what tree? I instead see
a much larger function body for update_tasks_nodemask(). I am looking
in a number of places, including 522dba7134d6b2e5821d3457f7941ec34f668e6d
in Linus's git tree.
Thanx, Paul
KOSAKI Motohiro
> > > On Thu, Mar 11, 2010 at 02:46:15PM +0900, KOSAKI Motohiro wrote:
> > > > rcu lockdep detected cpuset have wrong rcu usage.
> > > > the fixing is trivial. but I wonder why don't cpuset_being_rebound assignment
> > > > and read need a memory barrier pairing?
> > >
> > > The fix is in -tip, commit 99ee4ca746dda71326db7645463b4075ac1d665c.
> > >
> > > This is an initialization-time use of rcu_dereference(), so no other
> > > task has a reference to this data. Hence it is constant. Other uses
> > > of this code operate on shared data structures, which might change at
> > > any time.
> >
> > thanks. I haven't notice such commit.
> >
> > I think you are talking about task_cs(current) accessing and you are right
> > in such point.
> > but I'm talking cpuset_being_rebound global variable.
> >
> > update_tasks_nodemask() has following code
> >
> > static void update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem,
> > struct ptr_heap *heap)
> > {
> > cpuset_being_rebound = cs; /* start transaction */
> > cgroup_scan_tasks(&scan);
> > cpuset_being_rebound = NULL; /* end transaction */
> > }
>
> Hmmm... What commit are you looking at in what tree? I instead see
> a much larger function body for update_tasks_nodemask(). I am looking
> in a number of places, including 522dba7134d6b2e5821d3457f7941ec34f668e6d
> in Linus's git tree.
Ahh, I'm sorry. I wrote essential piece of the function instead
full cut-n-paste.
Plus, my previous explanation was too little and unclear. I don't think
your commit is wrong. it is definitely right. I only talked about I think
current_cpuset_is_being_rebound() has another sick.