[bug] lockdep warning: module_mutex vs. ftrace_lock

[Miklos Szeredi]

=======================================================
[ 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

other info that might help us debug this:

1 lock held by modprobe/3184:
 #0:  (module_mutex){+.+.+.}, at: [<ffffffff8026a539>] sys_init_module+0x3f/0x1d3

stack backtrace:
Pid: 3184, comm: modprobe Not tainted 2.6.29-09854-gd508afb-dirty #6
Call Trace:
 [<ffffffff8025fba1>] print_circular_bug_tail+0xc5/0xd0
 [<ffffffff80261067>] __lock_acquire+0x101b/0x1668
 [<ffffffff80267905>] ? find_symbol_in_section+0x39/0xda
 [<ffffffff80266a52>] ? each_symbol_in_section+0x3a/0x7a
 [<ffffffff802617a2>] lock_acquire+0xee/0x112
 [<ffffffff80277e71>] ? ftrace_convert_nops+0x32/0x267
 [<ffffffff804fe0a6>] mutex_lock_nested+0x4f/0x305
 [<ffffffff80277e71>] ? ftrace_convert_nops+0x32/0x267
 [<ffffffff8020af16>] ? ftrace_call+0x5/0x2b
 [<ffffffff80277e71>] ftrace_convert_nops+0x32/0x267
 [<ffffffff802780bd>] ftrace_init_module+0x17/0x19
 [<ffffffff8026a011>] load_module+0x1122/0x160b
 [<ffffffff8025f3a5>] ? trace_hardirqs_on_caller+0x114/0x138
 [<ffffffff8026a556>] sys_init_module+0x5c/0x1d3
 [<ffffffff8020b21b>] system_call_fastpath+0x16/0x1b
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