user/sven/linux.git/kernel/trace/trace_output.c, branch v6.2.8

tracing: Make sure trace_printk() can output as soon as it can be used

2023-01-24T16:27:29Z

Currently trace_printk() can be used as soon as early_trace_init() is called from start_kernel(). But if a crash happens, and "ftrace_dump_on_oops" is set on the kernel command line, all you get will be: [ 0.456075] -0 0dN.2. 347519us : Unknown type 6 [ 0.456075] -0 0dN.2. 353141us : Unknown type 6 [ 0.456075] -0 0dN.2. 358684us : Unknown type 6 This is because the trace_printk() event (type 6) hasn't been registered yet. That gets done via an early_initcall(), which may be early, but not early enough. Instead of registering the trace_printk() event (and other ftrace events, which are not trace events) via an early_initcall(), have them registered at the same time that trace_printk() can be used. This way, if there is a crash before early_initcall(), then the trace_printk()s will actually be useful. Link: https://lkml.kernel.org/r/20230104161412.019f6c55@gandalf.local.home Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Fixes: e725c731e3bb1 ("tracing: Split tracing initialization into two for early initialization") Reported-by: "Joel Fernandes (Google)" Tested-by: Joel Fernandes (Google) Signed-off-by: Steven Rostedt (Google)

tracing: Fix some checker warnings

2022-12-10T18:36:05Z

Fix some checker warnings in the trace code by adding __printf attributes to a number of trace functions and their declarations. Changes: ======== ver #2) - Dropped the fix for the unconditional tracing_max_lat_fops decl[1]. Link: https://lore.kernel.org/r/20221205180617.9b9d3971cbe06ee536603523@kernel.org/ [1] Link: https://lore.kernel.org/r/166992525941.1716618.13740663757583361463.stgit@warthog.procyon.org.uk/ # v1 Link: https://lkml.kernel.org/r/167023571258.382307.15314866482834835192.stgit@warthog.procyon.org.uk Signed-off-by: David Howells Signed-off-by: Steven Rostedt (Google)

tracing: Optimize event type allocation with IDA

2022-11-24T00:08:31Z

After commit 060fa5c83e67 ("tracing/events: reuse trace event ids after overflow"), trace events with dynamic type are linked up in list 'ftrace_event_list' through field 'trace_event.list'. Then when max event type number used up, it's possible to reuse type number of some freed one by traversing 'ftrace_event_list'. As instead, using IDA to manage available type numbers can make codes simpler and then the field 'trace_event.list' can be dropped. Since 'struct trace_event' is used in static tracepoints, drop 'trace_event.list' can make vmlinux smaller. Local test with about 2000 tracepoints, vmlinux reduced about 64KB: before：-rwxrwxr-x 1 root root 76669448 Nov 8 17:14 vmlinux after： -rwxrwxr-x 1 root root 76604176 Nov 8 17:15 vmlinux Link: https://lkml.kernel.org/r/20221110020319.1259291-1-zhengyejian1@huawei.com Signed-off-by: Zheng Yejian Acked-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google)

tracing: Remove usage of list iterator after the loop body

2022-04-27T21:19:30Z

In preparation to limit the scope of the list iterator variable to the traversal loop, use a dedicated pointer to point to the found element [1]. Before, the code implicitly used the head when no element was found when using &pos->list. Since the new variable is only set if an element was found, the head needs to be used explicitly if the variable is NULL. Link: https://lkml.kernel.org/r/20220427170734.819891-2-jakobkoschel@gmail.com Cc: Ingo Molnar Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1] Signed-off-by: Jakob Koschel Signed-off-by: Steven Rostedt (Google)

tracing: Use WARN instead of printk and WARN_ON

2022-04-26T21:58:52Z

Use `WARN(cond, ...)` instead of `if (cond)` + `printk(...)` + `WARN_ON(1)`. Link: https://lkml.kernel.org/r/20220424131932.3606-1-guozhengkui@vivo.com Suggested-by: Steven Rostedt Signed-off-by: Guo Zhengkui Signed-off-by: Steven Rostedt (Google)

tracing: Account bottom half disabled sections.

2022-01-13T21:23:04Z

Disabling only bottom halves via local_bh_disable() disables also preemption but this remains invisible to tracing. On a CONFIG_PREEMPT kernel one might wonder why there is no scheduling happening despite the N flag in the trace. The reason might be the a rcu_read_lock_bh() section. Add a 'b' to the tracing output if in task context with disabled bottom halves. Link: https://lkml.kernel.org/r/YbcbtdtC/bjCKo57@linutronix.de Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Steven Rostedt

tracing: Show kretprobe unknown indicator only for kretprobe_trampoline

2021-10-01T01:24:08Z

ftrace shows "[unknown/kretprobe'd]" indicator all addresses in the kretprobe_trampoline, but the modified address by kretprobe should be only kretprobe_trampoline+0. Link: https://lkml.kernel.org/r/163163056044.489837.794883849706638013.stgit@devnote2 Signed-off-by: Masami Hiramatsu Acked-by: Steven Rostedt (VMware) Tested-by: Andrii Nakryiko Signed-off-by: Steven Rostedt (VMware)

kprobes: treewide: Make it harder to refer kretprobe_trampoline directly

2021-10-01T01:24:06Z

Since now there is kretprobe_trampoline_addr() for referring the address of kretprobe trampoline code, we don't need to access kretprobe_trampoline directly. Make it harder to refer by renaming it to __kretprobe_trampoline(). Link: https://lkml.kernel.org/r/163163045446.489837.14510577516938803097.stgit@devnote2 Suggested-by: Ingo Molnar Signed-off-by: Masami Hiramatsu Signed-off-by: Steven Rostedt (VMware)

tracing: Add migrate-disabled counter to tracing output.

2021-09-03T23:42:35Z

migrate_disable() forbids task migration to another CPU. It is available since v5.11 and has already users such as highmem or BPF. It is useful to observe this task state in tracing which already has other states like the preemption counter. Instead of adding the migrate disable counter as a new entry to struct trace_entry, which would extend the whole struct by four bytes, it is squashed into the preempt-disable counter. The lower four bits represent the preemption counter, the upper four bits represent the migrate disable counter. Both counter shouldn't exceed 15 but if they do, there is a safety net which caps the value at 15. Add the migrate-disable counter to the trace entry so it shows up in the trace. Due to the users mentioned above, it is already possible to observe it: | bash-1108 [000] ...21 73.950578: rss_stat: mm_id=2213312838 curr=0 type=MM_ANONPAGES size=8192B | bash-1108 [000] d..31 73.951222: irq_disable: caller=flush_tlb_mm_range+0x115/0x130 parent=ptep_clear_flush+0x42/0x50 | bash-1108 [000] d..31 73.951222: tlb_flush: pages:1 reason:local mm shootdown (3) The last value is the migrate-disable counter. Things that popped up: - trace_print_lat_context() does not print the migrate counter. Not sure if it should. It is used in "verbose" mode and uses 8 digits and I'm not sure ther is something processing the value. - trace_define_common_fields() now defines a different variable. This probably breaks things. No ide what to do in order to preserve the old behaviour. Since this is used as a filter it should be split somehow to be able to match both nibbles here. Link: https://lkml.kernel.org/r/20210810132625.ylssabmsrkygokuv@linutronix.de Signed-off-by: Thomas Gleixner [bigeasy: patch description.] Signed-off-by: Sebastian Andrzej Siewior [ SDR: Removed change to common_preempt_count field name ] Signed-off-by: Steven Rostedt (VMware)

trace: Add timerlat tracer

2021-06-25T23:57:24Z

The timerlat tracer aims to help the preemptive kernel developers to found souces of wakeup latencies of real-time threads. Like cyclictest, the tracer sets a periodic timer that wakes up a thread. The thread then computes a *wakeup latency* value as the difference between the *current time* and the *absolute time* that the timer was set to expire. The main goal of timerlat is tracing in such a way to help kernel developers. Usage Write the ASCII text "timerlat" into the current_tracer file of the tracing system (generally mounted at /sys/kernel/tracing). For example: [root@f32 ~]# cd /sys/kernel/tracing/ [root@f32 tracing]# echo timerlat > current_tracer It is possible to follow the trace by reading the trace trace file: [root@f32 tracing]# cat trace # tracer: timerlat # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # || / # |||| ACTIVATION # TASK-PID CPU# |||| TIMESTAMP ID CONTEXT LATENCY # | | | |||| | | | | -0 [000] d.h1 54.029328: #1 context irq timer_latency 932 ns <...>-867 [000] .... 54.029339: #1 context thread timer_latency 11700 ns -0 [001] dNh1 54.029346: #1 context irq timer_latency 2833 ns <...>-868 [001] .... 54.029353: #1 context thread timer_latency 9820 ns -0 [000] d.h1 54.030328: #2 context irq timer_latency 769 ns <...>-867 [000] .... 54.030330: #2 context thread timer_latency 3070 ns -0 [001] d.h1 54.030344: #2 context irq timer_latency 935 ns <...>-868 [001] .... 54.030347: #2 context thread timer_latency 4351 ns The tracer creates a per-cpu kernel thread with real-time priority that prints two lines at every activation. The first is the *timer latency* observed at the *hardirq* context before the activation of the thread. The second is the *timer latency* observed by the thread, which is the same level that cyclictest reports. The ACTIVATION ID field serves to relate the *irq* execution to its respective *thread* execution. The irq/thread splitting is important to clarify at which context the unexpected high value is coming from. The *irq* context can be delayed by hardware related actions, such as SMIs, NMIs, IRQs or by a thread masking interrupts. Once the timer happens, the delay can also be influenced by blocking caused by threads. For example, by postponing the scheduler execution via preempt_disable(), by the scheduler execution, or by masking interrupts. Threads can also be delayed by the interference from other threads and IRQs. The timerlat can also take advantage of the osnoise: traceevents. For example: [root@f32 ~]# cd /sys/kernel/tracing/ [root@f32 tracing]# echo timerlat > current_tracer [root@f32 tracing]# echo osnoise > set_event [root@f32 tracing]# echo 25 > osnoise/stop_tracing_total_us [root@f32 tracing]# tail -10 trace cc1-87882 [005] d..h... 548.771078: #402268 context irq timer_latency 1585 ns cc1-87882 [005] dNLh1.. 548.771082: irq_noise: local_timer:236 start 548.771077442 duration 4597 ns cc1-87882 [005] dNLh2.. 548.771083: irq_noise: reschedule:253 start 548.771083017 duration 56 ns cc1-87882 [005] dNLh2.. 548.771086: irq_noise: call_function_single:251 start 548.771083811 duration 2048 ns cc1-87882 [005] dNLh2.. 548.771088: irq_noise: call_function_single:251 start 548.771086814 duration 1495 ns cc1-87882 [005] dNLh2.. 548.771091: irq_noise: call_function_single:251 start 548.771089194 duration 1558 ns cc1-87882 [005] dNLh2.. 548.771094: irq_noise: call_function_single:251 start 548.771091719 duration 1932 ns cc1-87882 [005] dNLh2.. 548.771096: irq_noise: call_function_single:251 start 548.771094696 duration 1050 ns cc1-87882 [005] d...3.. 548.771101: thread_noise: cc1:87882 start 548.771078243 duration 10909 ns timerlat/5-1035 [005] ....... 548.771103: #402268 context thread timer_latency 25960 ns For further information see: Documentation/trace/timerlat-tracer.rst Link: https://lkml.kernel.org/r/71f18efc013e1194bcaea1e54db957de2b19ba62.1624372313.git.bristot@redhat.com Cc: Phil Auld Cc: Sebastian Andrzej Siewior Cc: Kate Carcia Cc: Jonathan Corbet Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Alexandre Chartre Cc: Clark Willaims Cc: John Kacur Cc: Juri Lelli Cc: Borislav Petkov Cc: "H. Peter Anvin" Cc: x86@kernel.org Cc: linux-doc@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Daniel Bristot de Oliveira Signed-off-by: Steven Rostedt (VMware)