Messages in this thread | | | Subject | Re: Question on lockdep and MAX_LOCK_DEPTH | From | Steven Rostedt <> | Date | Tue, 05 Feb 2013 21:52:04 -0500 |
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On Tue, 2013-02-05 at 18:26 -0800, Ben Greear wrote: > Well, here it is..something is calling rcu_read_lock lots and lots,
Or a bug in the way lockdep handles rcu mappings.
> it seems. Any way to get a better idea of where those calls are > made?
Yeah, with ftrace.
> 96 locks held by swapper/0/0: > #0: (rcu_read_lock){.+.+..}, at: [<ffffffff81476836>] rcu_read_lock+0x0/0x6f > #1: (rcu_read_lock){.+.+..}, at: [<ffffffff81476836>] rcu_read_lock+0x0/0x6f [...] > #92: (rcu_read_lock){.+.+..}, at: [<ffffffff81476836>] rcu_read_lock+0x0/0x6f > #93: (&(&wl->cfg_spin_lock)->rlock){..-...}, at: [<ffffffffa07bc4d0>] handle_rcv+0x15d/0x1dd [wanlink] > #94: (&wl_threads[q].my_wq){..-...}, at: [<ffffffff810abe4d>] __wake_up+0x1d/0x48 > #95: (&p->pi_lock){-.-.-.}, at: [<ffffffff810b09c1>] try_to_wake_up+0x29/0x20b
If you haven't already configured ftrace into your kernel, can you please do so. Specifically:
CONFIG_FUNCTION_TRACER=y CONFIG_FUNCTION_GRAPH_TRACER=y CONFIG_DYNAMIC_FTRACE=y
Then, before triggering this, run the following as root:
# mount -t debugfs nodev /sys/kernel/debug # cd /sys/kernel/debug/tracing # echo net_rx_action > set_graph_function # echo function_graph > current_tracer
In the kernel, where you added the above dump, before any of the printks happen, add this too:
trace_printk("BUG\n"); tracing_off();
This will stop the trace at the point of the error. The trace_printk() is a nice way to see the trace too.
Then after you trigger the bug, do the following:
cat /sys/kernel/debug/tracing/trace
and reply with that.
To turn tracing on again (because the tracing_off() disabled it), you can do:
echo 1 > /sys/kernel/debug/tracing/tracing_on
Careful not to do "echo 1> ..." ;-)
-- Steve
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