deadlock in lttng_ust_init

[Daniel d'Andrada]

Happens when running tests for https://code.launchpad.net/~dandrader/qtmir/content-hub-clipboard/+merge/303863 by CI.

This is the backtrace of where it gets stuck:
#0 0xffffffff in __pthread_mutex_unlock_usercnt (mutex=0xb6fff514 <_rtld_global+1220>, decr=1) at pthread_mutex_unlock.c:51
#1 0xffffffff in tls_get_addr_tail (ti=0xb637021c, dtv=0xb3757008, the_map=<optimized out>) at dl-tls.c:778
#2 0xffffffff in lttng_ust_init () at /usr/include/urcu/static/urcu-bp.h:158
#3 0xffffffff in lttng_ust_init () at lttng-ust-comm.c:369
#4 0xffffffff in lttng_ust_init () at lttng-ust-comm.c:1481
#5 0xffffffff in call_init (l=<optimized out>, argc=argc@entry=1, argv=argv@entry=0xbefff3d4, env=env@entry=0xbefff3dc) at dl-init.c:72
#6 0xffffffff in _dl_init (env=<optimized out>, argv=<optimized out>, argc=<optimized out>, l=<optimized out>) at dl-init.c:30
#7 0xffffffff in _dl_init (main_map=0xb6fff958, argc=1, argv=0xbefff3d4, env=0xbefff3dc) at dl-init.c:120
#8 0xffffffff in _dl_start_user () at /lib/ld-linux-armhf.so.3

It gets stuck during initialization, more specifically, inside lttng_fixup_urcu_bp_tls()

[Gerry Boland (gerboland)]

This issue was worked around, but with a far-from-ideal solution

[Simon Marchi (simon-marchi)]

Which version of liblttng-ust is that?

[Mathieu Desnoyers (mathieu-desnoyers)]

It seems odd that touching a shared object TLS (which triggers a TLS fixup) from a constructor would deadlock. Which version of glibc are you using ?

[Daniel d'Andrada (dandrader)]

It might have something to do with arm or chroot envs (likely what CI does) as tests run fine on my amd64 desktop but deadlock in a chroot on an arm device (like mako or flo).

[Daniel d'Andrada (dandrader)]

But on CI it also deadlocks in amd64.

[Daniel d'Andrada (dandrader)]

liblttng-ust 2.7.1-1~vividoverlay1
libglib2.0 2.44.1-1ubuntu1

About comments #4 and #5: what seems more relevant is actually ubuntu release/pkg versions since my desktop runs xenial+stable-phone-overlay whereas my arm devices run vivid+stable-phone-overlay.

[Mathieu Desnoyers (mathieu-desnoyers)]

What is your glibc version ? You provided your libglib version which is unrelated to lttng-ust.

Or are you using Android bionic libc... ?

[Daniel d'Andrada (dandrader)]

libc6 2.21-0ubuntu4.0.1

[Michael Jeanson (mjeanson)]

Looks like a glibc 2.21 bug with TLS constructors, see:

https://bugzilla.redhat.com/show_bug.cgi?id=1223055

Seems to be fixed upstream by these commits:
https://github.com/bminor/glibc/commit/e400f3ccd36fe91d432cc7d45b4ccc799dece763
https://github.com/bminor/glibc/commit/90b37cac8b5a3e1548c29d91e3e0bff1014d2e5c