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Re: Need help to interpret pthread_mutex_t structure as printed by gdb
Sure, I can take a look! Just send the instruction on how to setup the
environment.
On 16/08/2016 19:53, Olle Blomgren wrote:
> I have test case that fails 9 out of 10 times on my machine. Do I send
> the code and instructions to you on this mail address? The code will
> be GPL:ed before release but I don't want it to float around on he
> Internet just yet. I want to send it outside this conversation if
> that's ok?
>
> On Tue, Aug 16, 2016 at 10:44 PM, Adhemerval Zanella
> <adhemerval.zanella@linaro.org> wrote:
>> For thread race conditions checks I usually ran with Thread Sanitizer
>> (both gcc and clang uses it).
>>
>> But again, bug reports for runtime issues in default usage modes are
>> usually debugged with *reproducible* testcase. It could be either a snippet
>> that stresses the issue or a more complex scenario on how to trigger the
>> issue.
>>
>> What it is somewhat frustrating is report with partial debug information
>> where one must constantly assume or guess scenarios about the origin
>> environment.
>>
>> So if you could provide a way to reproduce this issue it would be
>> *really* helpful to check what it is really happening.
>>
>> On 16/08/2016 16:53, Olle Blomgren wrote:
>>> I have now run valgrind tools memcheck, helgrind and drd on both
>>> client and server. The latter two are intended for MT programs using a
>>> pthread implementation. When I run the tools on the client side, the
>>> hang never occurs. When I run the tools on the server the hang occurs
>>> as usual. Although the hang occurs there is nothing in the logs that
>>> suggests an error that would cause the hang.
>>>
>>> When I use the helgrind tool it is possible to attach to the valgrind
>>> GDB server with a GDB client and query all the known mutexes and ask
>>> to see if any are held. This query reports 0 locked mutexes although
>>> the client hangs on a mutex it believes is locked, as I pass the query
>>> (monitor info locks).
>>>
>>> I have also run the Linux GRUB memtest86+ to ensure my RAM is
>>> physically ok, and it is.
>>>
>>> Do you have any debug tools or any other hints on what I can try to
>>> crack this on my own? If not, I would really appreciate sending my
>>> code to build and run on an x86_64 machine at the hands of someone
>>> more knowledgeable than myself.
>>>
>>>
>>> On Mon, Aug 15, 2016 at 11:45 PM, Adhemerval Zanella
>>> <adhemerval.zanella@linaro.org> wrote:
>>>>
>>>>
>>>> On 15/08/2016 18:14, Olle Blomgren wrote:
>>>>>> Could you provide the glibc version, a complete backtrace of both processes
>>>>>> and if possible a testcase?
>>>>>
>>>>> I use glibc-2.23.
>>>>> I have downloaded the source and built it with debug symbols. Full
>>>>> back traces follows below.
>>>>> Client back trace + printout of offending mutex. (This is the one that hangs)
>>>>> -------------------------------------------------------------------------------------------------------------------
>>>>> Thread 3 (Thread 0x7ff8d1fcc700 (LWP 14005)):
>>>>> #0 0x00007ff8d231b82d in poll () at ../sysdeps/unix/syscall-template.S:84
>>>>> #1 0x00007ff8d2b39434 in _daemon_monitor (attr=0x7ff8d2da8300
>>>>> <_mon_thr_attr>) at mam.c:1346
>>>>> #2 0x00007ff8d2db03e4 in start_thread (arg=0x7ff8d1fcc700) at
>>>>> pthread_create.c:333
>>>>> #3 0x00007ff8d23248ad in clone () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
>>>>>
>>>>> Thread 2 (Thread 0x7ff8d15cb700 (LWP 14006)):
>>>>> #0 __lll_lock_wait () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
>>>>> #1 0x00007ff8d2db2a75 in __GI___pthread_mutex_lock
>>>>> (mutex=0x7ff8d16ac810) at ../nptl/pthread_mutex_lock.c:80
>>>>> #2 0x00007ff8d2b1f962 in lch_lock (name=919552, type=LCH_EXCL,
>>>>> tx=0x7ff8d3446080, ctx=0x7ff8c4001110)
>>>>> at lch.c:124
>>>>> #3 0x00007ff8d2b40c1c in _get_page_get_entry (entry=0x7ff8d15cab80,
>>>>> nbr_bytes=8, ctx=0x7ff8c4001110)
>>>>> at pge.c:1194
>>>>> #4 0x00007ff8d2b41b36 in pge_alloc_entry (entry=0x7ff8d15cab80,
>>>>> nbr_bytes=8, page_sz=1 '\001',
>>>>> ctx=0x7ff8c4001110) at pge.c:1416
>>>>> #5 0x00007ff8d2b5d0bf in api_int_setup_entry
>>>>> (entry_arr=0x7ff8d15cacb8, page_ptr=0x7ff8d15cac88,
>>>>> page_ref=0x7ff8d15cac80, lr=0x7ff8d15cad50, meta=0xf68d50,
>>>>> tx=0x7ff8d3446080, nbr_entries=1, sct=0,
>>>>> ctx=0x7ff8c4001110) at api_int.c:47
>>>>> #6 0x00007ff8d2b5b410 in hope_new (tx=0x7ff8c4000cd0,
>>>>> elm_type=0x40b1c9 "NoColl", nv_list=0x40adf9 "tjing")
>>>>> at hope.c:2495
>>>>> #7 0x0000000000405d6d in _new1 (attr=0x0) at api_tests.c:1579
>>>>> #8 0x00007ff8d2db03e4 in start_thread (arg=0x7ff8d15cb700) at
>>>>> pthread_create.c:333
>>>>> #9 0x00007ff8d23248ad in clone () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
>>>>>
>>>>> Thread 1 (Thread 0x7ff8d34e0700 (LWP 14004)):
>>>>> #0 0x00007ff8d2db164d in pthread_join (threadid=140706641131264,
>>>>> thread_return=0x0) at pthread_join.c:90
>>>>> #1 0x0000000000406252 in _scan_1new40000_1read_1lockmod5remove_3thr
>>>>> (tc=30, print_desc_only=0)
>>>>> at api_tests.c:1682
>>>>> #2 0x000000000040a1b5 in _all_test_cases (tc=30, nbr_updates=0,
>>>>> start_value=0, name=0x0,
>>>>> ref=18446744073709551615, print_desc_only=0) at api_tests.c:2981
>>>>> #3 0x000000000040a784 in main (argc=4, argv=0x7fffed178988) at api_tests.c:3084
>>>>> (gdb) t 2
>>>>> [Switching to thread 2 (Thread 0x7ff8d15cb700 (LWP 14006))]
>>>>> #1 0x00007ff8d2db2a75 in __GI___pthread_mutex_lock
>>>>> (mutex=0x7ff8d16ac810) at ../nptl/pthread_mutex_lock.c:80
>>>>> 80 LLL_MUTEX_LOCK (mutex);
>>>>> (gdb) f 1
>>>>> #1 0x00007ff8d2db2a75 in __GI___pthread_mutex_lock
>>>>> (mutex=0x7ff8d16ac810) at ../nptl/pthread_mutex_lock.c:80
>>>>> 80 LLL_MUTEX_LOCK (mutex);
>>>>> (gdb) p *mutex
>>>>> $2 = {__data = {__lock = 0, __count = 0, __owner = 0, __nusers = 0,
>>>>> __kind = 0, __spins = 0, __elision = 0,
>>>>> __list = {__prev = 0x0, __next = 0x0}}, __size = '\000' <repeats
>>>>> 39 times>, __align = 0}
>>>>>
>>>>>
>>>>> Server back trace (All threads are just waiting around.)
>>>>> ------------------------------------------------------------------------
>>>>> Thread 6 (Thread 0x7f0686b45700 (LWP 14094)):
>>>>> #0 pthread_cond_wait@@GLIBC_2.3.2 () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
>>>>> #1 0x00007f0687838d8b in migrator (attr=0x7f0687c4f758) at hsh_int.c:207
>>>>> #2 0x00007f06875fb3e4 in start_thread (arg=0x7f0686b45700) at
>>>>> pthread_create.c:333
>>>>> #3 0x00007f0686e2d8ad in clone () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
>>>>>
>>>>> Thread 5 (Thread 0x7f0684b41700 (LWP 14098)):
>>>>> #0 pthread_cond_timedwait@@GLIBC_2.3.2 () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_timedwait.S:225
>>>>> #1 0x00007f0687896555 in _do_checkpoint (attr=0x0) at ckp.c:1411
>>>>> #2 0x00007f06875fb3e4 in start_thread (arg=0x7f0684b41700) at
>>>>> pthread_create.c:333
>>>>> #3 0x00007f0686e2d8ad in clone () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
>>>>>
>>>>> Thread 4 (Thread 0x7f0685342700 (LWP 14097)):
>>>>> #0 pthread_cond_wait@@GLIBC_2.3.2 () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
>>>>> #1 0x00007f0687838d8b in migrator (attr=0x7f0687c51280) at hsh_int.c:207
>>>>> #2 0x00007f06875fb3e4 in start_thread (arg=0x7f0685342700) at
>>>>> pthread_create.c:333
>>>>> #3 0x00007f0686e2d8ad in clone () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
>>>>>
>>>>> Thread 3 (Thread 0x7f0685b43700 (LWP 14096)):
>>>>> #0 pthread_cond_wait@@GLIBC_2.3.2 () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
>>>>> #1 0x00007f06878541bc in _rm_log (attr=0x0) at tlg.c:1527
>>>>> #2 0x00007f06875fb3e4 in start_thread (arg=0x7f0685b43700) at
>>>>> pthread_create.c:333
>>>>> #3 0x00007f0686e2d8ad in clone () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
>>>>>
>>>>> Thread 2 (Thread 0x7f0686344700 (LWP 14095)):
>>>>> #0 pthread_cond_wait@@GLIBC_2.3.2 () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
>>>>> #1 0x00007f0687853110 in flush_log_buffer (attr=0x0) at tlg.c:1385
>>>>> #2 0x00007f06875fb3e4 in start_thread (arg=0x7f0686344700) at
>>>>> pthread_create.c:333
>>>>> #3 0x00007f0686e2d8ad in clone () at
>>>>> ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
>>>>>
>>>>> Thread 1 (Thread 0x7f0687cef700 (LWP 14093)):
>>>>> #0 0x00007f0686e264f3 in select () at ../sysdeps/unix/syscall-template.S:84
>>>>> #1 0x00007f068785dcf0 in _daemon_server_loop (attr=0x7ffff2d255d0) at mam.c:730
>>>>> #2 0x00007f068785e1bc in mam_daemon_server_run (ctx=0x7ffff2d255d0)
>>>>> at mam.c:860
>>>>> #3 0x00007f0687870053 in dae_init (instance=0x212d180
>>>>> "/tmp/func_api", force=1, ctx=0x7ffff2d255d0)
>>>>> at dae.c:297
>>>>> #4 0x00007f068785bf4a in _do_start_daemon (ctx=0x7ffff2d255d0) at clu.c:320
>>>>> #5 0x00007f068785c388 in clu_execute (ctx=0x7ffff2d255d0) at clu.c:449
>>>>> #6 0x0000000000400994 in main (argc=6, argv=0x7ffff2d25b58) at db.c:21
>>>>>
>>>>> I can see that it is always server thread #5 that interferes with the
>>>>> hanging client thread in the following way:
>>>>> Server thread acquires mutex X.
>>>>> Client thread acquires mutex X (it sits waiting for the server thread
>>>>> to release mutex X).
>>>>> Server thread releases mutex X and continues its work...
>>>>> Client thread never wakes up. It continues to hang on mutex X.
>>>>>
>>>>> I have written a test program to try to provoke the same access
>>>>> pattern but I cannot make the same thing happen.
>>>>> I can see that the same access pattern:
>>>>> 1) server acquires mutex X
>>>>> 2) client acquires mutex X
>>>>> 3) server releases mutex X
>>>>> 4) client acquires mutex X
>>>>> completes successfully numerous times before the client hangs as shown above.
>>>>>
>>>>> Can you give me hints on how to continue further or do you want me to
>>>>> send my code to you?
>>>>> As seen above the hardware is x86_64.
>>>>>
>>>>> Brs
>>>>> /Olle
>>>>
>>>> I think either a testcase or a way to reproduce this issue would be the
>>>> way to proceed since current log is still inconclusive. I tried to check
>>>> on sourceware bug database to check some fixed issue since 2.19, but you
>>>> seemed to already checked with a more recent one.
>>>>
>>>> I strongly recommend you to try first a memory checker (valgrind, asan)
>>>> and/or a thread checker (tsan) to see if you are doing something wrong.