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9e45e39dc2
linux/kernel/trace
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Steven Rostedt (Google) 9e45e39dc2 ring-buffer: Do not update before stamp when switching sub-buffers 
The ring buffer timestamps are synchronized by two timestamp placeholders.
One is the "before_stamp" and the other is the "write_stamp" (sometimes
referred to as the "after stamp" but only in the comments. These two
stamps are key to knowing how to handle nested events coming in with a
lockless system.

When moving across sub-buffers, the before stamp is updated but the write
stamp is not. There's an effort to put back the before stamp to something
that seems logical in case there's nested events. But as the current event
is about to cross sub-buffers, and so will any new nested event that happens,
updating the before stamp is useless, and could even introduce new race
conditions.

The first event on a sub-buffer simply uses the sub-buffer's timestamp
and keeps a "delta" of zero. The "before_stamp" and "write_stamp" are not
used in the algorithm in this case. There's no reason to try to fix the
before_stamp when this happens.

As a bonus, it removes a cmpxchg() when crossing sub-buffers!

Link: https://lore.kernel.org/linux-trace-kernel/20231211114420.36dde01b@gandalf.local.home

Cc: stable@vger.kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Fixes: a389d86f7f ("ring-buffer: Have nested events still record running time stamp")
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2023-12-12 20:55:45 -05:00
..
rv tracing/tools: Updates for 6.4 2023-04-28 16:11:26 -07:00
blktrace.c block: remove more NULL checks after bdev_get_queue() 2023-02-21 09:23:22 -07:00
bpf_trace.c bpf: Add __bpf_kfunc_{start,end}_defs macros 2023-11-01 22:33:53 -07:00
bpf_trace.h
error_report-traces.c
fgraph.c tracing: arm64: Avoid missing-prototype warnings 2023-07-12 12:06:04 -04:00
fprobe.c Probes updates for v6.7: 2023-11-01 16:15:42 -10:00
ftrace_internal.h tracing: arm64: Avoid missing-prototype warnings 2023-07-12 12:06:04 -04:00
ftrace.c ftrace: Use LIST_HEAD to initialize clear_hash 2023-09-01 21:18:38 -04:00
Kconfig Probes updates for v6.5: 2023-06-30 10:44:53 -07:00
kprobe_event_gen_test.c tracing: Fix wrong return in kprobe_event_gen_test.c 2023-03-19 12:20:48 -04:00
Makefile tracing/probes: Move finding func-proto API and getting func-param API to trace_btf 2023-08-23 09:39:45 +09:00
pid_list.c tracing: Cleanup double word in comment 2022-04-26 17:58:50 -04:00
pid_list.h
power-traces.c
preemptirq_delay_test.c
rethook.c kprobes: unused header files removed 2023-10-24 10:04:59 +09:00
ring_buffer_benchmark.c ring_buffer: Remove unused "event" parameter 2022-11-23 19:08:30 -05:00
ring_buffer.c ring-buffer: Do not update before stamp when switching sub-buffers 2023-12-12 20:55:45 -05:00
rpm-traces.c
synth_event_gen_test.c tracing: Always use canonical ftrace path 2023-02-18 14:34:09 -05:00
trace_benchmark.c tracing: Add numeric delta time to the trace event benchmark 2022-09-26 13:01:09 -04:00
trace_benchmark.h tracing: Add numeric delta time to the trace event benchmark 2022-09-26 13:01:09 -04:00
trace_boot.c tracing/boot: Test strscpy() against less than zero for error 2023-07-05 10:30:49 -04:00
trace_branch.c
trace_btf.c tracing/probes: Add a function to search a member of a struct/union 2023-08-23 09:40:16 +09:00
trace_btf.h tracing/probes: Add a function to search a member of a struct/union 2023-08-23 09:40:16 +09:00
trace_clock.c
trace_dynevent.c tracing: Free buffers when a used dynamic event is removed 2022-11-23 19:07:12 -05:00
trace_dynevent.h
trace_entries.h tracing: Add back FORTIFY_SOURCE logic to kernel_stack event structure 2023-07-30 18:11:44 -04:00
trace_eprobe.c tracing/eprobe: drop unneeded breaks 2023-10-10 01:03:48 +09:00
trace_event_perf.c tracing/perf: Use strndup_user instead of kzalloc/strncpy_from_user 2022-11-23 19:08:31 -05:00
trace_events_filter_test.h
trace_events_filter.c tracing: Have trace_event_file have ref counters 2023-11-01 23:44:44 -04:00
trace_events_hist.c tracing/histograms: Simplify last_cmd_set() 2023-10-23 13:31:14 -04:00
trace_events_inject.c tracing: Have event inject files inc the trace array ref count 2023-09-07 16:38:54 -04:00
trace_events_synth.c tracing: Have the user copy of synthetic event address use correct context 2023-11-01 23:46:05 -04:00
trace_events_trigger.c tracing: Fix kernel-doc warnings in trace_events_trigger.c 2023-07-28 19:59:03 -04:00
trace_events_user.c tracing/user_events: Allow events to persist for perfmon_capable users 2023-10-03 22:29:43 -04:00
trace_events.c tracing: Have trace_event_file have ref counters 2023-11-01 23:44:44 -04:00
trace_export.c tracing: Add back FORTIFY_SOURCE logic to kernel_stack event structure 2023-07-30 18:11:44 -04:00
trace_fprobe.c tracing: fprobe-event: Fix to check tracepoint event and return 2023-11-10 20:06:12 +09:00
trace_functions_graph.c function_graph: Support recording and printing the return value of function 2023-06-20 18:38:37 -04:00
trace_functions.c
trace_hwlat.c tracing: Remove extra space at the end of hwlat_detector/mode 2023-09-01 21:00:00 -04:00
trace_irqsoff.c tracing: Fix memleak due to race between current_tracer and trace 2023-08-17 13:49:37 -04:00
trace_kdb.c
trace_kprobe_selftest.c tracing: arm64: Avoid missing-prototype warnings 2023-07-12 12:06:04 -04:00
trace_kprobe_selftest.h
trace_kprobe.c tracing/kprobes: Fix the order of argument descriptions 2023-11-11 08:00:43 +09:00
trace_mmiotrace.c
trace_nop.c
trace_osnoise.c tracing/timerlat: Add user-space interface 2023-06-22 10:39:56 -04:00
trace_output.c fs: create helper file_user_path() for user displayed mapped file path 2023-10-19 11:03:15 +02:00
trace_output.h tracing: Add "fields" option to show raw trace event fields 2023-03-29 06:52:08 -04:00
trace_preemptirq.c cpuidle: tracing, preempt: Squash _rcuidle tracing 2023-01-31 15:01:46 +01:00
trace_printk.c
trace_probe_kernel.h tracing/probes: Fix to record 0-length data_loc in fetch_store_string*() if fails 2023-07-14 17:04:58 +09:00
trace_probe_tmpl.h tracing/probes: Fix to record 0-length data_loc in fetch_store_string*() if fails 2023-07-14 17:04:58 +09:00
trace_probe.c tracing/probes: Add string type check with BTF 2023-08-23 09:41:13 +09:00
trace_probe.h tracing/kprobes: Return EADDRNOTAVAIL when func matches several symbols 2023-10-20 22:10:41 +09:00
trace_recursion_record.c tracing: Use trace_create_file() to simplify creation of tracefs entries 2022-05-26 21:12:52 -04:00
trace_sched_switch.c sched/tracing: Append prev_state to tp args instead 2022-05-12 00:37:11 +02:00
trace_sched_wakeup.c tracing: Fix memleak due to race between current_tracer and trace 2023-08-17 13:49:37 -04:00
trace_selftest_dynamic.c
trace_selftest.c tracing: Have function_graph selftest call cond_resched() 2023-05-28 21:15:46 -04:00
trace_seq.c tracing: Move readpos from seq_buf to trace_seq 2023-10-20 12:16:10 -04:00
trace_stack.c
trace_stat.c
trace_stat.h
trace_synth.h tracing: Allow synthetic events to pass around stacktraces 2023-01-25 10:31:24 -05:00
trace_syscalls.c bpf: Change syscall_nr type to int in struct syscall_tp_t 2023-10-13 12:39:36 -07:00
trace_uprobe.c Probes updates for v6.6: 2023-09-02 11:10:50 -07:00
trace.c tracing: Update snapshot buffer on resize if it is allocated 2023-12-12 19:00:38 -05:00
trace.h tracing: Have trace_event_file have ref counters 2023-11-01 23:44:44 -04:00
tracing_map.c tracing: Remove unused variable 'dups' 2022-10-03 12:20:31 -04:00
tracing_map.h tracing: Remove unused extern declaration tracing_map_set_field_descr() 2023-07-23 11:08:14 -04:00