Fix Python agent (double thread, same sessiond) + Python example #12
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It is possible that one of the session daemons left its agent.port file on the file system, for example when killed with SIGKILL. It is also common that both those session daemons use the same port for listening to agent connections. In this case, if one session daemon is running, but two agent.port files exist, the Python agent would connect its two threads to the same session daemon, leading to everything done twice: list shows events twice, tracing records events twice, etc. This patch ensures that if two agent.port files are found and have the same content, only one thread is used. Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
|
merged into master and stable-2.7, thanks! Mathieu |
compudj
pushed a commit
that referenced
this pull request
Dec 9, 2021
Observed issue
==============
Applications which transitively dlopen() a library which, in turn,
dlopen() providers crash when they are compiled with clang or
if LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP is defined.
Core was generated by `././myapp.exe'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x00007fa94f860bc2 in check_event_provider (probe_desc=<optimized out>) at lttng-probes.c:153
153 if (!check_type_provider(field->type)) {
[Current thread is 1 (Thread 0x7fa94fcbc740 (LWP 511754))]
(gdb) bt
#0 0x00007fa94f860bc2 in check_event_provider (probe_desc=<optimized out>) at lttng-probes.c:153
#1 lttng_ust_probe_register (desc=0x7fa94fe9dc80 <lttng_ust__probe_desc___embedded_sys>)
at lttng-probes.c:242
#2 0x00007fa94fe9ba3c in lttng_ust__tracepoints__ptrs_destroy ()
at /usr/include/lttng/tracepoint.h:590
#3 0x00007fa94fedfe2e in call_init () from /lib64/ld-linux-x86-64.so.2
#4 0x00007fa94fedff1c in _dl_init () from /lib64/ld-linux-x86-64.so.2
#5 0x00007fa94fdf7d45 in _dl_catch_exception () from /usr/lib/libc.so.6
#6 0x00007fa94fee420a in dl_open_worker () from /lib64/ld-linux-x86-64.so.2
#7 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6
#8 0x00007fa94fee39bb in _dl_open () from /lib64/ld-linux-x86-64.so.2
#9 0x00007fa94fe8d36c in ?? () from /usr/lib/libdl.so.2
#10 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6
#11 0x00007fa94fdf7db3 in _dl_catch_error () from /usr/lib/libc.so.6
#12 0x00007fa94fe8db99 in ?? () from /usr/lib/libdl.so.2
#13 0x00007fa94fe8d3f8 in dlopen () from /usr/lib/libdl.so.2
#14 0x00007fa94fecc647 in mon_constructeur () at mylib.cpp:20
#15 0x00007fa94fedfe2e in call_init () from /lib64/ld-linux-x86-64.so.2
#16 0x00007fa94fedff1c in _dl_init () from /lib64/ld-linux-x86-64.so.2
#17 0x00007fa94fdf7d45 in _dl_catch_exception () from /usr/lib/libc.so.6
#18 0x00007fa94fee420a in dl_open_worker () from /lib64/ld-linux-x86-64.so.2
#19 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6
#20 0x00007fa94fee39bb in _dl_open () from /lib64/ld-linux-x86-64.so.2
#21 0x00007fa94fe8d36c in ?? () from /usr/lib/libdl.so.2
#22 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6
#23 0x00007fa94fdf7db3 in _dl_catch_error () from /usr/lib/libc.so.6
#24 0x00007fa94fe8db99 in ?? () from /usr/lib/libdl.so.2
#25 0x00007fa94fe8d3f8 in dlopen () from /usr/lib/libdl.so.2
#26 0x00005594f478c18c in main ()
Cause
=====
Building tracepoint instrumentation as C++ using clang causes
LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP to be defined due to a
compiler version detection problem addressed by another patch.
However, building with LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP
defined still results in the crash.
When LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP is defined, the
lttng_ust_event_field lttng_ust__event_fields__[...] structure is
initialized by dynamically-allocating field structures for the various
fields.
As the initialization can't be performed statically, it is performed at
run-time _after_ the execution of the library constructors has
completed.
Moreover, the generated initialization
function of the provider (lttng_ust__events_init__[...]) is declared as being a library
constructor. Hence, this causes it to run before the
tracepoint fields structures has a chance to be initialized.
This all results in a NULL pointer dereference during the validation of
the fields.
Solution
========
When building providers as C++, the initialization function is defined
as the constructor of a class. This class is, in turn, instantiated in
an anonymous namespace.
For the purposes of this patch, the use of an anonymous namespace is
equivalent to declaring the instance as 'static', but it is preferred in
C++11.
Known drawbacks
===============
None.
References
==========
A reproducer is available:
https://github.com/jgalar/ust-clang-reproducer
Problem initially reported on dotnet/runtime's issue tracker:
dotnet/runtime#62398
Relevant LTTng-UST issue:
https://bugs.lttng.org/issues/1339
Fixes: #1339
Change-Id: I51cfbe74729bd45e2613a30bc8de17e08ea8233d
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
compudj
pushed a commit
that referenced
this pull request
Dec 9, 2021
Observed issue
==============
Applications which transitively dlopen() a library which, in turn,
dlopen() providers crash when they are compiled with clang or
if LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP is defined.
Core was generated by `././myapp.exe'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x00007fa94f860bc2 in check_event_provider (probe_desc=<optimized out>) at lttng-probes.c:153
153 if (!check_type_provider(field->type)) {
[Current thread is 1 (Thread 0x7fa94fcbc740 (LWP 511754))]
(gdb) bt
#0 0x00007fa94f860bc2 in check_event_provider (probe_desc=<optimized out>) at lttng-probes.c:153
#1 lttng_ust_probe_register (desc=0x7fa94fe9dc80 <lttng_ust__probe_desc___embedded_sys>)
at lttng-probes.c:242
#2 0x00007fa94fe9ba3c in lttng_ust__tracepoints__ptrs_destroy ()
at /usr/include/lttng/tracepoint.h:590
#3 0x00007fa94fedfe2e in call_init () from /lib64/ld-linux-x86-64.so.2
#4 0x00007fa94fedff1c in _dl_init () from /lib64/ld-linux-x86-64.so.2
#5 0x00007fa94fdf7d45 in _dl_catch_exception () from /usr/lib/libc.so.6
#6 0x00007fa94fee420a in dl_open_worker () from /lib64/ld-linux-x86-64.so.2
#7 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6
#8 0x00007fa94fee39bb in _dl_open () from /lib64/ld-linux-x86-64.so.2
#9 0x00007fa94fe8d36c in ?? () from /usr/lib/libdl.so.2
#10 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6
#11 0x00007fa94fdf7db3 in _dl_catch_error () from /usr/lib/libc.so.6
#12 0x00007fa94fe8db99 in ?? () from /usr/lib/libdl.so.2
#13 0x00007fa94fe8d3f8 in dlopen () from /usr/lib/libdl.so.2
#14 0x00007fa94fecc647 in mon_constructeur () at mylib.cpp:20
#15 0x00007fa94fedfe2e in call_init () from /lib64/ld-linux-x86-64.so.2
#16 0x00007fa94fedff1c in _dl_init () from /lib64/ld-linux-x86-64.so.2
#17 0x00007fa94fdf7d45 in _dl_catch_exception () from /usr/lib/libc.so.6
#18 0x00007fa94fee420a in dl_open_worker () from /lib64/ld-linux-x86-64.so.2
#19 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6
#20 0x00007fa94fee39bb in _dl_open () from /lib64/ld-linux-x86-64.so.2
#21 0x00007fa94fe8d36c in ?? () from /usr/lib/libdl.so.2
#22 0x00007fa94fdf7ce8 in _dl_catch_exception () from /usr/lib/libc.so.6
#23 0x00007fa94fdf7db3 in _dl_catch_error () from /usr/lib/libc.so.6
#24 0x00007fa94fe8db99 in ?? () from /usr/lib/libdl.so.2
#25 0x00007fa94fe8d3f8 in dlopen () from /usr/lib/libdl.so.2
#26 0x00005594f478c18c in main ()
Cause
=====
Building tracepoint instrumentation as C++ using clang causes
LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP to be defined due to a
compiler version detection problem addressed by another patch.
However, building with LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP
defined still results in the crash.
When LTTNG_UST_ALLOCATE_COMPOUND_LITERAL_ON_HEAP is defined, the
lttng_ust_event_field lttng_ust__event_fields__[...] structure is
initialized by dynamically-allocating field structures for the various
fields.
As the initialization can't be performed statically, it is performed at
run-time _after_ the execution of the library constructors has
completed.
Moreover, the generated initialization
function of the provider (lttng_ust__events_init__[...]) is declared as being a library
constructor. Hence, this causes it to run before the
tracepoint fields structures has a chance to be initialized.
This all results in a NULL pointer dereference during the validation of
the fields.
Solution
========
When building providers as C++, the initialization function is defined
as the constructor of a class. This class is, in turn, instantiated in
an anonymous namespace.
For the purposes of this patch, the use of an anonymous namespace is
equivalent to declaring the instance as 'static', but it is preferred in
C++11.
Known drawbacks
===============
None.
References
==========
A reproducer is available:
https://github.com/jgalar/ust-clang-reproducer
Problem initially reported on dotnet/runtime's issue tracker:
dotnet/runtime#62398
Relevant LTTng-UST issue:
https://bugs.lttng.org/issues/1339
Fixes: #1339
Change-Id: I51cfbe74729bd45e2613a30bc8de17e08ea8233d
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
mjeanson
pushed a commit
to mjeanson/lttng-ust
that referenced
this pull request
Oct 5, 2022
Eliminate the following deadlock by calling libc close directly when
called from within the 2.12 fd tracker locking. The 2.13 locks always
need to be taken outside of the 2.12 locks. In the scenario below,
Thread 3 (lttng-ust 2.12 listener thread) takes the locks in the wrong
order.
Thread 3 (Thread 0x7f7679247700 (LWP 621683) "hello-ust"):
#0 __lll_lock_wait (futex=futex@entry=0x7f767a392b60 <ust_safe_guard_fd_mutex>, private=0) at lowlevellock.c:52
lttng#1 0x00007f767a39d843 in __GI___pthread_mutex_lock (mutex=0x7f767a392b60 <ust_safe_guard_fd_mutex>) at ../nptl/pthread_mutex_lock.c:80
-> 2.13 locks fd tracker
2.13 lttng#2 0x00007f767a37ff82 in lttng_ust_lock_fd_tracker_orig () at fd-tracker.c:163
2.13 lttng#3 0x00007f767a380b66 in lttng_ust_safe_close_fd_orig (fd=3, close_cb=0x7f767a56b070 <__GI___close>) at fd-tracker.c:385
2.13 lttng#4 0x00007f767a6e5557 in close (fd=3) at lttng-ust-fd.c:101
2.12 lttng#5 0x00007f767a297e7d in ustcomm_connect_unix_sock (pathname=0x7f767a32bc64 <local_apps+36> "/home/compudj/.lttng/lttng-ust-sock-8", timeout=3000) at lttng-ust-comm.c:157
-> 2.12 listener thread locks fd tracker
-> 2.12 listener thread locks ust_lock
2.12 lttng#6 0x00007f767a2a1f77 in ust_listener_thread (arg=0x7f767a32bc40 <local_apps>) at lttng-ust-comm.c:1591
lttng#7 0x00007f767a39aea7 in start_thread (arg=<optimized out>) at pthread_create.c:477
lttng#8 0x00007f767a57aaef in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
Thread 2 (Thread 0x7f7678a46700 (LWP 621682) "hello-ust"):
#0 __lll_lock_wait (futex=futex@entry=0x7f767a32f780 <ust_mutex>, private=0) at lowlevellock.c:52
lttng#1 0x00007f767a39d843 in __GI___pthread_mutex_lock (mutex=0x7f767a32f780 <ust_mutex>) at ../nptl/pthread_mutex_lock.c:80
2.12 lttng#2 0x00007f767a29da59 in ust_lock () at lttng-ust-comm.c:167
2.12 lttng#3 0x00007f767a2a1d95 in ust_listener_thread (arg=0x7f767a329be0 <global_apps>) at lttng-ust-comm.c:1558
lttng#4 0x00007f767a39aea7 in start_thread (arg=<optimized out>) at pthread_create.c:477
lttng#5 0x00007f767a57aaef in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
Thread 1 (Thread 0x7f767a33a040 (LWP 621681) "hello"):
#0 __lll_lock_wait (futex=futex@entry=0x7f767a32f720 <ust_safe_guard_fd_mutex>, private=0) at lowlevellock.c:52
lttng#1 0x00007f767a39d843 in __GI___pthread_mutex_lock (mutex=0x7f767a32f720 <ust_safe_guard_fd_mutex>) at ../nptl/pthread_mutex_lock.c:80
-> 2.12 lock fd tracker
2.12 lttng#2 0x00007f767a29c37c in lttng_ust_lock_fd_tracker () at lttng-ust-fd-tracker.c:153
2.12 lttng#3 0x00007f767a29ceba in lttng_ust_safe_close_fd (fd=4, close_cb=0x7f767a56b070 <__GI___close>) at lttng-ust-fd-tracker.c:341
2.13 lttng#4 0x00007f767a380b06 in lttng_ust_safe_close_fd_chain (fd=4, close_cb=0x7f767a56b070 <__GI___close>) at fd-tracker.c:348
2.13 lttng#5 0x00007f767a380b5c in lttng_ust_safe_close_fd_orig (fd=4, close_cb=0x7f767a56b070 <__GI___close>) at fd-tracker.c:379
2.13 lttng#6 0x00007f767a6e5557 in close (fd=4) at lttng-ust-fd.c:101
-> 2.13 lock fd tracker
2.13 lttng#7 0x00007f767a43b5e6 in lttng_ust_elf_destroy (elf=0x55b870f044c0) at elf.c:352
2.13 lttng#8 0x00007f767a3f2797 in get_elf_info (bin_data=0x7ffd5481ef70) at lttng-ust-statedump.c:296
2.13 lttng#9 0x00007f767a3f283f in extract_baddr (bin_data=0x7ffd5481ef70) at lttng-ust-statedump.c:319
2.13 lttng#10 0x00007f767a3f3173 in extract_bin_info_events (info=0x7ffd5481fff0, size=64, _data=0x7ffd54820098) at lttng-ust-statedump.c:518
lttng#11 0x00007f767a5b3ad5 in __GI___dl_iterate_phdr (callback=0x7f767a3f2f5a <extract_bin_info_events>, data=0x7ffd54820098) at dl-iteratephdr.c:75
2.13 lttng#12 0x00007f767a3f32c5 in lttng_ust_dl_update_orig (ip=0x7f767a3cb599 <lttng_ust_ctor+683>) at lttng-ust-statedump.c:574
2.13 lttng#13 0x00007f767a3f33f7 in lttng_ust_statedump_init () at lttng-ust-statedump.c:638
2.13 lttng#14 0x00007f767a3cb599 in lttng_ust_ctor () at lttng-ust-comm.c:2246
2.13 lttng#15 0x00007f767a3ccaad in lttng_ust_after_fork_child (restore_sigset=0x7ffd548207e0) at lttng-ust-comm.c:2577
2.13 lttng#16 0x00007f767a6f687f in fork () at ustfork.c:271
lttng#17 0x000055b8705f1034 in make_child ()
lttng#18 0x000055b8705daacc in execute_command_internal ()
lttng#19 0x000055b8705ddcf5 in execute_command ()
lttng#20 0x000055b8705df951 in ?? ()
lttng#21 0x000055b8705daf79 in execute_command_internal ()
lttng#22 0x000055b8705ddcf5 in execute_command ()
lttng#23 0x000055b8705c49db in reader_loop ()
lttng#24 0x000055b8705c3668 in main ()
Getting the state of lttng-ust 2.12 ust_fd_mutex_nest TLS variable is
not straightforward, because it is a static variable (internal state).
The trick used here is to rely on the "lttng_ust_safe_close_fd" symbol
exported by lttng-ust 2.12. When passed fd=-1, with a close_cb which
simply returns 0, we can use the resulting return values to determine
the current state (zero vs nonzero) of the ust_fd_mutex_nest TLS
variable without any side-effect other than temporarily taking/releasing
the fd tracker lock when ust_fd_mutex_nest==0.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I6b95e0fd607abccd67aadf35ec96c19877394b16
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