LTTng bugs repository: Issueshttps://bugs.lttng.org/https://bugs.lttng.org/themes/lttng/favicon/a.ico?14249722912023-06-01T18:48:58ZLTTng bugs repository
Redmine LTTng-tools - Bug #1379 (New): Document behavior of live mode with per-pid UST buffershttps://bugs.lttng.org/issues/13792023-06-01T18:48:58ZMathieu Desnoyersmathieu.desnoyers@efficios.com
<p>There is a design limitation of per-pid UST buffers when used in live mode which should be documented.</p>
<p>Basically, because the per-pid buffers are reclaimed soon after the application exits, it may cause the events traced by a short-lived application to never appear in the output of a live trace when per-pid buffers are used.</p>
<p>This is caused by the fact that the live client periodically checks for new buffers, but there is no inherent reference kept on the streams before they disappear.</p>
<p>This means that the information will be available in the disk output of the trace, but it will be missing from the live mode output.</p>
<p>This could eventually be mitigated by keeping references to the streams received by the relay daemon which are of interest to a live client until they are referenced by the live client.</p> LTTng-tools - Bug #1378 (New): Document behavior of snapshot mode with per-pid UST buffershttps://bugs.lttng.org/issues/13782023-06-01T18:01:12ZMathieu Desnoyersmathieu.desnoyers@efficios.com
<p>We should document a design limitation of the per-pid UST buffers which can lead to unexpected results when used with the "snapshot" feature.</p>
<p>Basically, because the per-pid buffers lifetime is bound by the application using them (and the consumer daemon extracting data from them), they are freed almost immediately after the traced application exits. However, in a scenario where we are interested in capturing a snapshot of the content of flight recorder buffers soon after application exits (e.g. caused by a crash), those buffers are not available anymore a few milliseconds after the application exits.</p>
<p>We should document this design limitation, and eventually think about improvements (feature request ?) to allow a configurable delay after application exit during which the consumer daemon could keep references on the buffers so they are available for snapshot.</p> LTTng-tools - Feature #1341 (New): Introduce "--shm-path-ust" to clarify use vs documentationhttps://bugs.lttng.org/issues/13412021-12-07T20:53:52ZMathieu Desnoyersmathieu.desnoyers@efficios.com
<p>Considering that the "--shm-path" argument is documented as applying to all domains, but that currently the kernel domain does not support this argument, it leads us to a situation where users may budget their NVRAM for the space needed only for UST buffers, and eventually upgrade to a new LTTng version which would implement kernel support for shm-path. They would then face issues given the lack of available space.</p>
<p>I would recommend to add a new "--shm-path-ust" argument as an alias to "--shm-path", but document that it only applies to the UST domain. This way, users wishing to budget their NVRAM space only for UST tracing, but still perform kernel tracing in the same session, will be able to do so.</p> LTTng-tools - Bug #1340 (New): Document behavior of per-uid UST buffers with respect to asynchron...https://bugs.lttng.org/issues/13402021-12-07T20:22:28ZMathieu Desnoyersmathieu.desnoyers@efficios.com
<p>We should document a known design limitation of the per-uid UST buffers:</p>
<p>When using lttng-ust with per-uid buffers, there is a known design limitation<br />regarding process terminated by non-handled kill signals: if this occurs while<br />the buffer is being written to (between reserve and commit), it will cause the<br />rest of the per-cpu buffer to be unreadable. This applies to all events<br />recorded by all applications of the same user id for that particular CPU.<br />Recovering from this involves destroying and re-creating the tracing session.</p>
<p>If this kind of scenario is likely for you, you might want to consider using per-<br />pid buffers (lttng enable-channel -u --buffers-pid), which do not suffer from<br />this design limitation. The downside of per-pid buffers is that it allocates<br />more memory on your system for buffering, and adds extra overhead when<br />used with processes that have a short life-time.</p> LTTng-tools - Feature #1287 (New): Use abstract sockets for lttng-consumerd UST shared memory fileshttps://bugs.lttng.org/issues/12872020-10-13T15:35:32ZMathieu Desnoyersmathieu.desnoyers@efficios.com
<p>Abstract sockets (unix(7)) are not tied to the filesystem, and are available since Linux 2.2.</p>
<p>Those are Linux-specific.</p>
<p>Those are the same as regular unix domain but their first character of path is NULL. They have the benefit of not requiring unlinking of files left behind.</p>
<p>We could use those abstract sockets in lttng-consumerd on Linux.</p> LTTng-UST - Bug #1203 (New): Improve documentation of lttng-ust with daemonshttps://bugs.lttng.org/issues/12032019-10-07T15:51:26ZMathieu Desnoyersmathieu.desnoyers@efficios.com
<p>The lttng-ust(3) man page should be clarified regarding the scenarios where the liblttng-ust-fork.so wrapper is needed.</p>
<p>It should document that it is needed in scenarios where applications using fork(2), clone(2) (with CLONE_VM flag cleared), BSD's rfork(2), daemon(3), without <strong>immediately</strong> following those by an exec(3) family call. This includes scenarios where close(2) is used to close file descriptors before invoking exec(3), even though close(2) is listed as an async-signal-safe function.</p> LTTng-tools - Bug #987 (Confirmed): Incomplete string comparison patternhttps://bugs.lttng.org/issues/9872016-01-06T23:23:31ZMathieu Desnoyersmathieu.desnoyers@efficios.com
<p>In a few instances in lttng-tools, a string comparison pattern involving strncmp and strlen() to limit the length of the comparison is used.</p>
<p>One can quickly find them with:</p>
<p>grep -r -A 3 strncmp . | less -> search for strlen or strnlen</p>
<p>Many of those are OK: they indeed only want to match the beginning of the strings. However, this pattern is incorrectly used in cases where a full match is required, for instance:</p>
<p>ust-registry.c:ht_match_event()<br />./src/bin/lttng/commands/enable_channels.c: if (!strncmp(output_mmap, opt_output, strlen(output_mmap))) {<br />./src/bin/lttng/commands/enable_channels.c: } else if (!strncmp(output_splice, opt_output, strlen(output_splice))) {<br />./src/bin/lttng-sessiond/snapshot.c: if (!strncmp(output->name, name, strlen(name))) {</p> LTTng-modules - Bug #975 (Confirmed): execve compat syscall exit syscall value issuehttps://bugs.lttng.org/issues/9752015-11-08T16:03:18ZMathieu Desnoyersmathieu.desnoyers@efficios.com
<p>syscall_exit for execve changing the 32/64-bit compat mode for a process has wrong system call number on exit:</p>
<pre>
[19:36:57.188066018] (+0.000000616) sinkpad syscall_entry_execve: { cpu_id = 0 }, { filename = "/usr/bin/burnP6", argv = 0x7FFD275BBF40, envp = 0x7FFD275BBF50 }
[19:36:57.188162705] (+0.000000851) sinkpad module_get: { cpu_id = 0 }, { ip = 18446744071581118857, refcnt = 3, name = "binfmt_misc" }
[19:36:57.188170506] (+0.000000517) sinkpad module_put: { cpu_id = 0 }, { ip = 18446744071581118912, refcnt = 2, name = "binfmt_misc" }
[19:36:57.188630250] (+0.000000911) sinkpad random_get_random_bytes: { cpu_id = 0 }, { nbytes = 16, IP = 18446744071581461559 }
[19:36:57.188630781] (+0.000000531) sinkpad random_extract_entropy: { cpu_id = 0 }, { pool_name = "nonblocking", nbytes = 16, entropy_count = 0, IP = 18446744071583984742 }
[19:36:57.188634640] (+0.000001773) sinkpad sched_waking: { cpu_id = 0 }, { comm = "rngd", tid = 2177, prio = 120, target_cpu = 2 }
[19:36:57.188637855] (+0.000003215) sinkpad sched_stat_sleep: { cpu_id = 0 }, { comm = "rngd", tid = 2177, delay = 2656341 }
[19:36:57.188639681] (+0.000001826) sinkpad sched_wakeup: { cpu_id = 0 }, { comm = "rngd", tid = 2177, prio = 120, target_cpu = 2 }
[19:36:57.188641483] (+0.000000180) sinkpad power_cpu_idle: { cpu_id = 2 }, { state = 4294967295, cpu_id = 2 }
[19:36:57.188646080] (+0.000000644) sinkpad random_mix_pool_bytes_nolock: { cpu_id = 0 }, { pool_name = "nonblocking", bytes = 20, IP = 18446744071583981062 }
[19:36:57.188649456] (+0.000000788) sinkpad random_mix_pool_bytes_nolock: { cpu_id = 0 }, { pool_name = "nonblocking", bytes = 20, IP = 18446744071583981062 }
[19:36:57.188649704] (+0.000000248) sinkpad rcu_utilization: { cpu_id = 2 }, { s = "Start context switch" }
[19:36:57.188650149] (+0.000000182) sinkpad rcu_utilization: { cpu_id = 2 }, { s = "End context switch" }
[19:36:57.188652253] (+0.000001864) sinkpad sched_stat_wait: { cpu_id = 2 }, { comm = "rngd", tid = 2177, delay = 0 }
[19:36:57.188654080] (+0.000001827) sinkpad sched_switch: { cpu_id = 2 }, { prev_comm = "swapper/2", prev_tid = 0, prev_prio = 20, prev_state = 0, next_comm = "rngd", next_tid = 2177, next_prio = 20 }
[19:36:57.188658382] (+0.000000567) sinkpad sched_process_exec: { cpu_id = 0 }, { filename = "/usr/bin/burnP6", tid = 29058, old_tid = 29058 }
[19:36:57.188661040] (+0.000000020) sinkpad rcu_utilization: { cpu_id = 2 }, { s = "Start context switch" }
[19:36:57.188661415] (+0.000000375) sinkpad rcu_utilization: { cpu_id = 2 }, { s = "End context switch" }
[19:36:57.188662327] (+0.000000409) sinkpad sched_stat_runtime: { cpu_id = 2 }, { comm = "rngd", tid = 2177, runtime = 25827, vruntime = 1365908673 }
[19:36:57.188664216] (+0.000001266) sinkpad compat_syscall_exit_olduname: { cpu_id = 0 }, { ret = 0, name = 0 }
</pre> LTTng - Feature #968 (Feedback): lttng-modules kernel and user callstack contexthttps://bugs.lttng.org/issues/9682015-10-25T20:14:40ZMathieu Desnoyersmathieu.desnoyers@efficios.com
<p>Implementation from Francis Giraldeau reviewed and cleaned up available here:</p>
<p><a class="external" href="https://github.com/compudj/lttng-tools-dev/tree/callstack">https://github.com/compudj/lttng-tools-dev/tree/callstack</a><br /><a class="external" href="https://github.com/compudj/lttng-modules-dev/tree/callstack">https://github.com/compudj/lttng-modules-dev/tree/callstack</a></p>
<p>Documentation and tests are missing.</p> LTTng-UST - Feature #965 (New): Implement UST statedumphttps://bugs.lttng.org/issues/9652015-10-22T20:43:37ZMathieu Desnoyersmathieu.desnoyers@efficios.com
<p>Initial implementation: <a class="external" href="https://github.com/compudj/lttng-ust-dev/tree/statedump-notifier">https://github.com/compudj/lttng-ust-dev/tree/statedump-notifier</a></p>
<p>Missing tests in lttng-tools for this feature before we can merge it into lttng-ust.</p> LTTng-modules - Feature #964 (New): Implement support for persistent memory buffershttps://bugs.lttng.org/issues/9642015-10-22T20:41:43ZMathieu Desnoyersmathieu.desnoyers@efficios.comLTTng-modules - Feature #963 (New): Implement user-space stack dump contexthttps://bugs.lttng.org/issues/9632015-10-22T20:41:10ZMathieu Desnoyersmathieu.desnoyers@efficios.comLTTng-modules - Feature #962 (New): add x86 exceptions.h and irq_vectors.h instrumentation (and m...https://bugs.lttng.org/issues/9622015-10-22T19:47:19ZMathieu Desnoyersmathieu.desnoyers@efficios.comUserspace RCU - Feature #940 (New): Wire up sys membarrier on each architecturehttps://bugs.lttng.org/issues/9402015-09-26T16:00:41ZMathieu Desnoyersmathieu.desnoyers@efficios.comLTTng-UST - Feature #327 (On pause): Implement missing hostname contexthttps://bugs.lttng.org/issues/3272012-08-26T23:22:47ZMathieu Desnoyersmathieu.desnoyers@efficios.com
<p>To match features of lttng-modules.</p>