Messages in this thread | | | Subject | Re: __update_max_tr: rcu_read_lock() used illegally while idle! | From | Steven Rostedt <> | Date | Tue, 31 Jul 2012 09:44:13 -0400 |
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On Tue, 2012-07-31 at 20:10 +0800, Fengguang Wu wrote:
> Another note: the above __update_max_tr back trace only appear accasionally. > The more typical error messages look like this: > > [ 16.195315] Running tests on trace events: > [ 16.196586] Testing event kfree_skb: [ 16.200404] ------------[ cut here ]------------ > [ 16.201428] WARNING: at /c/wfg/linux/kernel/lockdep.c:3506 check_flags+0x125/0x154() > [ 16.203036] Hardware name: Bochs > [ 16.203763] Pid: 44, comm: rcu_torture_wri Not tainted 3.5.0+ #82 > [ 16.205067] Call Trace: > > [ 16.205640] [<c102a9f8>] warn_slowpath_common+0x63/0x78 > [ 16.206842] [<c10644ed>] ? check_flags+0x125/0x154 > [ 16.207865] [<c102aaa7>] warn_slowpath_null+0x14/0x18 > [ 16.208939] [<c10644ed>] check_flags+0x125/0x154 > [ 16.210009] [<c106522b>] lock_is_held+0x28/0x82 > [ 16.210023] [<c1031849>] ? _local_bh_enable_ip+0x9e/0x166 > [ 16.210023] [<c107d0ac>] rcu_read_lock_held+0x26/0x2c
This is caused by the function tracer. Every function can call this (even rcu_read_lock itself).
We use a schedule rcu to reference a structure, and call rcu_dereference_raw() to get it.
Perhaps we should just bypass the check?
Hmm, looking at this again, perhaps it needs the rcu_dereference_sched()? When this was first added (3f379b03) rcu_dereference_raw was:
#define rcu_dereference_raw(p) ({ \ typeof(p) _________p1 = ACCESS_ONCE(p); \ smp_read_barrier_depends(); \ (_________p1); \ })
With no check. In fact, the check called the raw. Now it's reversed. I'm thinking that we need a way to not have a check. Function tracing is *extremely* invasive. As I said, this gets called *by* rcu_read_lock()! I'm not sure we want checks involved here.
-- Steve
> [ 16.210023] [<c107d59d>] ftrace_ops_list_func+0x82/0xca > [ 16.210023] [<c1050ce8>] ? sub_preempt_count+0x5/0xf1 > [ 16.210023] [<c13e5699>] trace+0x13/0x1b > [ 16.210023] [<c10318ec>] ? _local_bh_enable_ip+0x141/0x166 > [ 16.210023] [<c1050ced>] ? sub_preempt_count+0xa/0xf1 > [ 16.210023] [<c1031849>] _local_bh_enable_ip+0x9e/0x166 > [ 16.210023] [<c1077fea>] ? rcu_torture_writer+0xa1/0x1c5 > [ 16.220592] [<c1031bc4>] local_bh_enable_ip+0xd/0xf > [ 16.220592] [<c13e3ff9>] _raw_spin_unlock_bh+0x34/0x37 > [ 16.220592] [<c1077fea>] rcu_torture_writer+0xa1/0x1c5 > [ 16.220592] [<c104544f>] kthread+0x6c/0x71 > [ 16.220592] [<c1077f49>] ? rcu_torture_barrier_cbs+0x199/0x199 > [ 16.220592] [<c10453e3>] ? insert_kthread_work+0xa8/0xa8 > [ 16.220592] [<c13e5662>] kernel_thread_helper+0x6/0x10 > > Thanks, > Fengguang
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