Hello, Mike.
Sorry about the delay. Was on vacation and then had a strep throat.
On Mon, Feb 20, 2017 at 11:15:23AM +0100, Mike Galbraith wrote:
> Running LTP on master.today (v4.10) with a seriously bloated PREEMPT
> config inspired box to emit the below.
>
> [ 7160.458996] ===============================
> [ 7160.463195] [ INFO: suspicious RCU usage. ]
> [ 7160.467387] 4.10.0-default #100 Tainted: G E
> [ 7160.472808] -------------------------------
> [ 7160.476999] ./include/linux/cgroup.h:435 suspicious
> rcu_dereference_check() usage!
> [ 7160.484576]
> [ 7160.484576] other info that might help us debug this:
> [ 7160.484576]
> [ 7160.492577]
> [ 7160.492577] rcu_scheduler_active = 2, debug_locks = 1
> [ 7160.499113] 1 lock held by pids_task1/19308:
> [ 7160.503390] #0: (&cgroup_threadgroup_rwsem){+++++.}, at:
> [<ffffffff81095b60>] _do_fork+0xf0/0x710
> [ 7160.512450]
> [ 7160.512450] stack backtrace:
> [ 7160.516810] CPU: 5 PID: 19308 Comm: pids_task1 Tainted: G E
> 4.10.0-default #100
> [ 7160.525239] Hardware name: IBM System x3550 M3 -[7944K3G]-/69Y5698 ,
> BIOS -[D6E150AUS-1.10]- 12/15/2010
> [ 7160.534965] Call Trace:
> [ 7160.537414] dump_stack+0x85/0xc9
> [ 7160.540732] lockdep_rcu_suspicious+0xd5/0x110
> [ 7160.545177] task_css.constprop.7+0x88/0x90
> [ 7160.549357] pids_can_fork+0x132/0x160
> [ 7160.553106] cgroup_can_fork+0x63/0xc0
That gotta be a spurious one coming from the incorrect
!CONFIG_PROVE_RCU definition of the task_css_set_check() macro.
Something like the following should fix it.
If you still have the .config around, can you please attach it? I'll
verify the fix and send out the fix.
Thanks.
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index f6b43fb..870ea9a 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -396,7 +396,7 @@ extern spinlock_t css_set_lock;
((task)->flags & PF_EXITING) || (__c))
#else
#define task_css_set_check(task, __c) \
- rcu_dereference((task)->cgroups)
+ rcu_dereference_check((task)->cgroups, (__c))
#endif
/**
