Note for docker users: "crash in libVallka getValue()"

[alexey001]

Version: 1.2.2-0ubuntu1-focalppa1 (self compiled same effect)
Crash on demo application websocket-mse-demo .

Backtrace:

Program terminated with signal SIGSEGV, Segmentation fault.
#0 __new_sem_getvalue (sem=0x0, sval=0x7ffddd6ddc94) at sem_getvalue.c:38
38 sem_getvalue.c: No such file or directory.
(gdb) bt
#0 __new_sem_getvalue (sem=0x0, sval=0x7ffddd6ddc94) at sem_getvalue.c:38
#1 0x00007f2e6b2b78c6 in SharedMemRingBufferBase::getValue() () from /lib/libValkka.so.1
#2 0x00007f2e6b2b7a31 in SharedMemRingBufferBase::zero() () from /lib/libValkka.so.1
#3 0x00007f2e6b2b8118 in SharedMemRingBufferBase::SharedMemRingBufferBase(char const*, int, unsigned long, int, bool) () from /lib/libValkka.so.1
#4 0x00007f2e6b2a5239 in FragMP4SharedMemRingBuffer::FragMP4SharedMemRingBuffer(char const*, int, unsigned long, int, bool) () from /lib/libValkka.so.1
#5 0x00007f2e6b2a548c in FragMP4ShmemFrameFilter::FragMP4ShmemFrameFilter(char const*, int, unsigned long, int) () from /lib/libValkka.so.1
#6 0x00007f2e6c9d371f in _wrap_new_FragMP4ShmemFrameFilter () from /usr/lib/python3/dist-packages/valkka/core/_valkka_core.so
#7 0x00000000005f2d6a in cfunction_call_varargs (kwargs=, args=,
func=<built-in method new_FragMP4ShmemFrameFilter of module object at remote 0x7f2e6ca3c4a0>) at ../Include/internal/pycore_pyerrors.h:13

OS:
cat /etc/os-release
NAME="Ubuntu"
VERSION="20.04.3 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04.3 LTS"
VERSION_ID="20.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=focal
UBUNTU_CODENAME=focal

(running in LXD container).

df -h | grep shm
tmpfs 16G 8.0K 16G 1% /dev/shm

ipcs -m

------ Shared Memory Segments --------
key shmid owner perms bytes nattch status

SIGSEGV occurs when run as regular user and root.

[elsampsa]

Thanks for the report.

A quick follow-up question: you have only seen this segfault when using the LXD container, right?

[alexey001]

Yes. I have not tried other options as my host system not debian-based (gentoo) and more work needs to be done to compile libvalkka.

[alexey001]

It looks like the problem is somewhere in my system. I will analyze more..

==24324== ---Thread-Announcement------------------------------------------
==24324==
==24324== Thread #1 is the program's root thread
==24324==
==24324== ----------------------------------------------------------------
==24324==
==24324== Thread #1's call to sem_open failed
==24324== with error code 13 (EACCES: Permission denied)
==24324== at 0x48445F4: sem_open (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_helgrind-amd64-linux.so)
==24324== by 0x5EF9FDE: SharedMemRingBufferBase::SharedMemRingBufferBase(char const*, int, unsigned long, int, bool) (in /usr/lib/libValkka.so.1.2.2)
==24324== by 0x5EE7238: FragMP4SharedMemRingBuffer::FragMP4SharedMemRingBuffer(char const*, int, unsigned long, int, bool) (in /usr/lib/libValkka.so.1.2.2)
==24324== by 0x5EE748B: FragMP4ShmemFrameFilter::FragMP4ShmemFrameFilter(char const*, int, unsigned long, int) (in /usr/lib/libValkka.so.1.2.2)
==24324== by 0x5C5771E: _wrap_new_FragMP4ShmemFrameFilter (in /usr/lib/python3/dist-packages/valkka/core/_valkka_core.so.1.2.2)
==24324== by 0x5F2D69: UnknownInlinedFun (call.c:758)
==24324== by 0x5F2D69: PyCFunction_Call (call.c:773)
==24324== by 0x5F300F: _PyObject_MakeTpCall (call.c:159)
==24324== by 0x5700F2: UnknownInlinedFun (abstract.h:125)
==24324== by 0x5700F2: UnknownInlinedFun (abstract.h:115)
==24324== by 0x5700F2: UnknownInlinedFun (ceval.c:4963)
==24324== by 0x5700F2: _PyEval_EvalFrameDefault (ceval.c:3469)
==24324== by 0x568D99: UnknownInlinedFun (ceval.c:741)
==24324== by 0x568D99: _PyEval_EvalCodeWithName (ceval.c:4298)
==24324== by 0x5F5B32: _PyFunction_Vectorcall (call.c:436)

[elsampsa]

thanks!

One detail: working with shared memory (and semaphores?) in containers, can give surprises. See for example the comments in libValkka's dockerhub page.

Could this be a problem with user rights in your container's /dev/shm folder? : link

[alexey001]

The problem was simple - I launched the application one time as a root and of course, after that the application could not open /dev/shmXXX (running as regular user). Probably it is worth providing for the analysis of the return code when opening shared memory dev's.

[elsampsa]

I will keep this open to remind me that using shared memory in docker containers can give surprises & this must be properly documented