Date: Thu, 23 Apr 2015 22:24:16 +0000 (GMT)
From: Eunbong Song <eunb.song@samsung.com>
Subject: Re: Re: [PATCH] tools/liblockdep: change current_obj from thread-local
 storage to non thread-local storage
To: Sasha Levin <sasha.levin@oracle.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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> On 04/23/2015 02:55 AM, Eunbong Song wrote:
>> current_obj is declared as a thread-local storage.
>> This prevent to detect locking  problem between multiple threads because
>> each thread has it's own current_obj. liblockdep can only detect locking problem in a single
>> thread. However, pthread_mutex_xxx, pthread_rwlock_xxx functions are mainly used for synchro
>> nization of data between multiple threads.
>> This patch changes current_obj to non thread-local storage. and current_obj.pid is getting
>> from getpid system call.

> um... It always worked with threads:

I am sorry for confusing you. I did some mistake with my test. 
Thanks for your reply. 

> $ cat tests/ABBA_threads.c
> #include 
> #include "common.h"

> pthread_mutex_t a, b;

> void *thread_a(void *arg)
> {
> LOCK_UNLOCK_2(a, b);

> return NULL;
> }

void *thread_b(void *arg)
{
LOCK_UNLOCK_2(b, a);

return NULL;
}

void main(void)
{
pthread_t ta, tb;

pthread_mutex_init(&a, NULL);
pthread_mutex_init(&b, NULL);

pthread_create(&ta, NULL, thread_a, NULL);
pthread_create(&tb, NULL, thread_b, NULL);

pthread_join(ta, NULL);
pthread_join(tb, NULL);
}
$ tests/ABBA_threads

======================================================
[ INFO: possible circular locking dependency detected ]
liblockdep 4.0.0
-------------------------------------------------------
ABBA_threads/12101 is trying to acquire lock:
(0x10bb700){......}, at: tests/ABBA_threads() [0x401333]

but task is already holding lock:
(0x10bb680){......}, at: tests/ABBA_threads() [0x401333]

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (0x10bb680){......}:
tests/ABBA_threads[0x4019d3]
tests/ABBA_threads[0x4036f6]
tests/ABBA_threads[0x4039c2]
tests/ABBA_threads[0x403fde]
tests/ABBA_threads[0x404aa7]
tests/ABBA_threads[0x405250]
tests/ABBA_threads[0x4053d3]
tests/ABBA_threads[0x4055cd]
tests/ABBA_threads[0x40135d]
tests/ABBA_threads[0x401395]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x80a5)[0x7f8e6e1dc0a5]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7f8e6df09cfd]

-> #0 (0x10bb700){......}:
tests/ABBA_threads[0x4019d3]
tests/ABBA_threads[0x402f51]
tests/ABBA_threads[0x4035c4]
tests/ABBA_threads[0x4039c2]
tests/ABBA_threads[0x403fde]
tests/ABBA_threads[0x404aa7]
tests/ABBA_threads[0x405565]
tests/ABBA_threads(pthread_mutex_lock+0x51)[0x4063fd]
tests/ABBA_threads[0x401333]
tests/ABBA_threads[0x4013c6]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x80a5)[0x7f8e6e1dc0a5]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7f8e6df09cfd]

other info that might help us debug this:

Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(0x10bb680);
                               lock(0x10bb700);
                               lock(0x10bb680);
  lock(0x10bb700);

*** DEADLOCK ***

2 locks held by ABBA_threads/12101:
#0:  (&b){......}, at: tests/ABBA_threads() [0x4013bc]
#1:  (0x10bb680){......}, at: tests/ABBA_threads() [0x401333]

stack backtrace:
tests/ABBA_threads[0x4016dd]
tests/ABBA_threads[0x40300b]
tests/ABBA_threads[0x4035c4]
tests/ABBA_threads[0x4039c2]
tests/ABBA_threads[0x403fde]
tests/ABBA_threads[0x404aa7]
tests/ABBA_threads[0x405565]
tests/ABBA_threads(pthread_mutex_lock+0x51)[0x4063fd]
tests/ABBA_threads[0x401333]
tests/ABBA_threads[0x4013c6]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x80a5)[0x7f8e6e1dc0a5]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7f8e6df09cfd]


Thanks,
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