* Mathieu Desnoyers ([email protected]) wrote: > * Mathieu Desnoyers ([email protected]) wrote: > > * Burton, Michael ([email protected]) wrote: > > > Mathieu, > > > > > > I think there is a deadlock scenario in UST, which has been causing my > > > problem. > > > > Good catch ! > > > > > > > > sessiond is started as root: > > > - creates global sockets ONLY > > > - DOES NOT CREATE shm in $HOME/lttng-ust-wait-<uid> > > > > > > application linked against ust is run as root: > > > - in lttng_ust_init constructor > > > - ust_listener_thread (local_apps) > > > - fails to connect to local_apps in $HOME/.lttng (as expected) > > > - prev_connect_failed=1 > > > - ust_unlock() > > > - restart > > > - wait_for_sessiond() > > > --> - ust_lock() > > > | - get_map_shm() > > > | - get_wait_shm() > > > DEADLOCK - shm_open() FAILS (not created by sessiond when run by root) > > > | - fork() (trying to create shared memory itself) > > > | - ust_before_fork() > > > ------------> - ust_lock() > > > > > > > > > You should be able to create this with an empty main, with no > > > tracepoints. As long as sessiond is started as root so > > > $HOME/lttng-ust-wait-<uid> is not created. You can also make the > > > lttng-ust constructor (lttng_ust_init) wait forever and then you'll be > > > able to see the deadlock in gdb without even leaving the > > > lttng_ust_init constructor. > > > > Ah, I see. This deadlock is caused by the interaction between > > liblttng-ust-libc-wrapper and liblttng-ust (the fork override is > > performed by liblttng-ust-libc-wrapper). I'll have to look into this > > issue further. More on that soon. > > Actually, I meant that it comes from interaction between > liblttng-ust-fork and liblttng-ust (sorry about the confusion above). > I'll see if I can provide a direct access to the fork() symbol to > liblttng-ust, using a weak symbol so it is defined even when > liblttng-ust-fork is not linked. > > More on that soon...
Fixed by master commit: commit e8508a495280a1396a0319a157409a7ea61ffc5a Author: Mathieu Desnoyers <[email protected]> Date: Wed Jun 13 04:26:34 2012 -0400 Fix: liblttng-ust-fork deadlock and merged into stable-2.0. Thanks for pointing out this important bug. Mathieu -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com _______________________________________________ lttng-dev mailing list [email protected] http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
