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Subject: Re: [bug] lockdep warning: module_mutex vs. ftrace_lock
From: Steven Rostedt <srostedt@redhat.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>, linux-kernel@vger.kernel.org,
       rusty@rustcorp.com.au, mingo@elte.hu
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References: <E1LrEGG-0000ag-Js@pomaz-ex.szeredi.hu>
	 <20090407183014.GA7531@nowhere>
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Date: Mon, 13 Apr 2009 10:08:27 -0400
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Sorry for the late reply, I just got back from San Fran, and I do not
check my Red Hat email while I'm traveling.


On Tue, 2009-04-07 at 20:30 +0200, Frederic Weisbecker wrote:
> On Tue, Apr 07, 2009 at 06:34:56PM +0200, Miklos Szeredi wrote:
> > =======================================================
> > [ INFO: possible circular locking dependency detected ]
> > 2.6.29-09854-gd508afb-dirty #6
> > -------------------------------------------------------
> > modprobe/3184 is trying to acquire lock:
> >  (ftrace_lock){+.+.+.}, at: [<ffffffff80277e71>] ftrace_convert_nops+0x32/0x267
> > 
> > but task is already holding lock:
> >  (module_mutex){+.+.+.}, at: [<ffffffff8026a539>] sys_init_module+0x3f/0x1d3
> > 
> > which lock already depends on the new lock.
> > 
> > 
> > the existing dependency chain (in reverse order) is:
> > 
> > -> #1 (module_mutex){+.+.+.}:
> >        [<ffffffff8026134a>] __lock_acquire+0x12fe/0x1668
> >        [<ffffffff802617a2>] lock_acquire+0xee/0x112
> >        [<ffffffff804fe0a6>] mutex_lock_nested+0x4f/0x305
> >        [<ffffffff8026709e>] module_update_tracepoints+0x1c/0x73
> >        [<ffffffff80274f74>] tracepoint_update_probes+0x21/0x23
> >        [<ffffffff8027510a>] tracepoint_probe_register+0x4a/0x68
> >        [<ffffffff80277cae>] register_ftrace_graph+0x2a9/0x30f
> >        [<ffffffff8027f928>] trace_selftest_startup_function_graph+0x2e/0xbb
> >        [<ffffffff8027fdc5>] register_tracer+0x151/0x26e
> >        [<ffffffff8070b942>] init_graph_trace+0x10/0x12
> >        [<ffffffff80209066>] do_one_initcall+0x5b/0x135
> >        [<ffffffff806fa5e4>] kernel_init+0x12f/0x185
> >        [<ffffffff8020c2ba>] child_rip+0xa/0x20
> >        [<ffffffffffffffff>] 0xffffffffffffffff
> > 
> > -> #0 (ftrace_lock){+.+.+.}:
> >        [<ffffffff80261067>] __lock_acquire+0x101b/0x1668
> >        [<ffffffff802617a2>] lock_acquire+0xee/0x112
> >        [<ffffffff804fe0a6>] mutex_lock_nested+0x4f/0x305
> >        [<ffffffff80277e71>] ftrace_convert_nops+0x32/0x267
> >        [<ffffffff802780bd>] ftrace_init_module+0x17/0x19
> >        [<ffffffff8026a011>] load_module+0x1122/0x160b
> >        [<ffffffff8026a556>] sys_init_module+0x5c/0x1d3
> >        [<ffffffff8020b21b>] system_call_fastpath+0x16/0x1b
> >        [<ffffffffffffffff>] 0xffffffffffffffff
> 
> 
> 
> Ah that's this ftrace/modules lock dependency that Steven told me about
> recently. Steven, do you know more about it now?

Yeah, I think I submitted a patch to fix that. I'll check my repo.

-- Steve


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