Re: Need help to interpret pthread_mutex_t structure as printed by gdb

[David Niklas <doark at mail dot com>]

On Wed, 17 Aug 2016 16:49:52 <ollemblomgren@gmail.com> wrote:

Forgive the top post.
I was wondering if this problem was ever solved (it's been ~2 weeks), it
interested me, though I'm just as baffled as anyone else.

Thanks,
David

> Source code and instructions have been sent. Thanks!
> 
> On Wed, Aug 17, 2016 at 1:16 AM, Adhemerval Zanella
> <adhemerval.zanella@linaro.org> wrote:
> > 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.