On Wed, 22 Oct 2014, Steven Rostedt wrote:
> > Still, the lockdep stacktrace is bogus and didn't really help
> > understanding this. Any idea why it's wrong?
>
> Could possibly be from a tail call?
Doesn't seem so:
(gdb) disassemble cpuidle_pause
Dump of assembler code for function cpuidle_pause:
0xffffffff81491880 <+0>: push %rbp
0xffffffff81491881 <+1>: xor %esi,%esi
0xffffffff81491883 <+3>: mov $0xffffffff81a9eb20,%rdi
0xffffffff8149188a <+10>: mov %rsp,%rbp
0xffffffff8149188d <+13>: callq 0xffffffff815b9ed0 <mutex_lock_nested>
0xffffffff81491892 <+18>: callq 0xffffffff81491680
<cpuidle_uninstall_idle_handler>
0xffffffff81491897 <+23>: mov $0xffffffff81a9eb20,%rdi
0xffffffff8149189e <+30>: callq 0xffffffff815bbe60 <mutex_unlock>
0xffffffff814918a3 <+35>: pop %rbp
0xffffffff814918a4 <+36>: retq
End of assembler dump.
(gdb) disassemble cpuidle_uninstall_idle_handler
Dump of assembler code for function cpuidle_uninstall_idle_handler:
0xffffffff81491680 <+0>: mov 0x159da32(%rip),%eax #
0xffffffff82a2f0b8 <enabled_devices>
0xffffffff81491686 <+6>: push %rbp
0xffffffff81491687 <+7>: mov %rsp,%rbp
0xffffffff8149168a <+10>: test %eax,%eax
0xffffffff8149168c <+12>: je 0xffffffff8149169d
<cpuidle_uninstall_idle_handler+29>
0xffffffff8149168e <+14>: movl $0x0,0x64794c(%rip) #
0xffffffff81ad8fe4 <initialized>
0xffffffff81491698 <+24>: callq 0xffffffff810cf9b0
<wake_up_all_idle_cpus>
0xffffffff8149169d <+29>: callq 0xffffffff810b47b0 <synchronize_sched>
0xffffffff814916a2 <+34>: pop %rbp
0xffffffff814916a3 <+35>: retq
End of assembler dump.
(gdb) disassemble synchronize_sched
Dump of assembler code for function synchronize_sched:
0xffffffff810b47b0 <+0>: push %rbp
0xffffffff810b47b1 <+1>: xor %edx,%edx
0xffffffff810b47b3 <+3>: mov $0xad5,%esi
0xffffffff810b47b8 <+8>: mov $0xffffffff817fad6d,%rdi
0xffffffff810b47bf <+15>: mov %rsp,%rbp
0xffffffff810b47c2 <+18>: callq 0xffffffff81075900 <__might_sleep>
0xffffffff810b47c7 <+23>: incl %gs:0xbaa0
0xffffffff810b47cf <+31>: mov 0x5587b2(%rip),%rdi #
0xffffffff8160cf88 <cpu_online_mask>
0xffffffff810b47d6 <+38>: mov $0x200,%esi
0xffffffff810b47db <+43>: callq 0xffffffff8130e710 <__bitmap_weight>
0xffffffff810b47e0 <+48>: decl %gs:0xbaa0
0xffffffff810b47e8 <+56>: cmp $0x1,%eax
0xffffffff810b47eb <+59>: jbe 0xffffffff810b4803 <synchronize_sched+83>
0xffffffff810b47ed <+61>: mov 0xbdf97d(%rip),%eax #
0xffffffff81c94170 <rcu_expedited>
0xffffffff810b47f3 <+67>: test %eax,%eax
0xffffffff810b47f5 <+69>: jne 0xffffffff810b4808 <synchronize_sched+88>
0xffffffff810b47f7 <+71>: mov $0xffffffff810b3d80,%rdi
0xffffffff810b47fe <+78>: callq 0xffffffff810b1b00 <wait_rcu_gp>
0xffffffff810b4803 <+83>: pop %rbp
0xffffffff810b4804 <+84>: retq
0xffffffff810b4805 <+85>: nopl (%rax)
0xffffffff810b4808 <+88>: callq 0xffffffff810b4820
<synchronize_sched_expedited>
0xffffffff810b480d <+93>: pop %rbp
0xffffffff810b480e <+94>: xchg %ax,%ax
0xffffffff810b4810 <+96>: retq
> > > ======================================================
> > > [ INFO: possible circular locking dependency detected ]
> > > 3.18.0-rc1-00069-gc2661b8 #1 Not tainted
> > > -------------------------------------------------------
> > > do_s2disk/2367 is trying to acquire lock:
> > > (cpuidle_lock){+.+.+.}, at: [<ffffffff814916c2>]
> > > cpuidle_pause_and_lock+0x12/0x20
> > >
> > > but task is already holding lock:
> > > (cpu_hotplug.lock#2){+.+.+.}, at: [<ffffffff810522ea>]
> > > cpu_hotplug_begin+0x4a/0x80
> > >
> > > which lock already depends on the new lock.
> > >
> > > the existing dependency chain (in reverse order) is:
> > >
> > > -> #1 (cpu_hotplug.lock#2){+.+.+.}:
> > > [<ffffffff81099fac>] lock_acquire+0xac/0x130
> > > [<ffffffff815b9f2c>] mutex_lock_nested+0x5c/0x3b0
> > > [<ffffffff81491892>] cpuidle_pause+0x12/0x30
>
> Where exactly does that address point to?
(gdb) disassemble cpuidle_pause
Dump of assembler code for function cpuidle_pause:
0xffffffff81491880 <+0>: push %rbp
0xffffffff81491881 <+1>: xor %esi,%esi
0xffffffff81491883 <+3>: mov $0xffffffff81a9eb20,%rdi
0xffffffff8149188a <+10>: mov %rsp,%rbp
0xffffffff8149188d <+13>: callq 0xffffffff815b9ed0 <mutex_lock_nested>
0xffffffff81491892 <+18>: callq 0xffffffff81491680
<cpuidle_uninstall_idle_handler>
0xffffffff81491897 <+23>: mov $0xffffffff81a9eb20,%rdi
0xffffffff8149189e <+30>: callq 0xffffffff815bbe60 <mutex_unlock>
0xffffffff814918a3 <+35>: pop %rbp
0xffffffff814918a4 <+36>: retq
--
Jiri Kosina
SUSE Labs
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