linux/kernel/trace/trace_events_synth.c, branch v6.17

tracing: Add guard(ring_buffer_nest)

2025-08-01T20:49:15Z

Some calls to the tracing ring buffer can happen when the ring buffer is already being written to by the same context (for example, a trace_printk() in between a ring_buffer_lock_reserve() and a ring_buffer_unlock_commit()). In order to not trigger the recursion detection, these functions use ring_buffer_nest_start() and ring_buffer_nest_end(). Create a guard() for these functions so that their use cases can be simplified and not need to use goto for the release. Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Link: https://lore.kernel.org/20250801203857.710501021@kernel.org Signed-off-by: Steven Rostedt (Google)

tracing: Do not add length to print format in synthetic events

2025-04-09T15:34:21Z

The following causes a vsnprintf fault: # echo 's:wake_lat char[] wakee; u64 delta;' >> /sys/kernel/tracing/dynamic_events # echo 'hist:keys=pid:ts=common_timestamp.usecs if !(common_flags & 0x18)' > /sys/kernel/tracing/events/sched/sched_waking/trigger # echo 'hist:keys=next_pid:delta=common_timestamp.usecs-$ts:onmatch(sched.sched_waking).trace(wake_lat,next_comm,$delta)' > /sys/kernel/tracing/events/sched/sched_switch/trigger Because the synthetic event's "wakee" field is created as a dynamic string (even though the string copied is not). The print format to print the dynamic string changed from "%*s" to "%s" because another location (__set_synth_event_print_fmt()) exported this to user space, and user space did not need that. But it is still used in print_synth_event(), and the output looks like: -0 [001] d..5. 193.428167: wake_lat: wakee=(efault)sshd-sessiondelta=155 sshd-session-879 [001] d..5. 193.811080: wake_lat: wakee=(efault)kworker/u34:5delta=58 -0 [002] d..5. 193.811198: wake_lat: wakee=(efault)bashdelta=91 bash-880 [002] d..5. 193.811371: wake_lat: wakee=(efault)kworker/u35:2delta=21 -0 [001] d..5. 193.811516: wake_lat: wakee=(efault)sshd-sessiondelta=129 sshd-session-879 [001] d..5. 193.967576: wake_lat: wakee=(efault)kworker/u34:5delta=50 The length isn't needed as the string is always nul terminated. Just print the string and not add the length (which was hard coded to the max string length anyway). Cc: stable@vger.kernel.org Cc: Mathieu Desnoyers Cc: Tom Zanussi Cc: Douglas Raillard Acked-by: Masami Hiramatsu (Google) Link: https://lore.kernel.org/20250407154139.69955768@gandalf.local.home Fixes: 4d38328eb442d ("tracing: Fix synth event printk format for str fields"); Signed-off-by: Steven Rostedt (Google)

tracing: Replace strncpy with memcpy for fixed-length substring copy

2025-03-25T21:44:32Z

checkpatch.pl reports the following warning: WARNING: Prefer strscpy, strscpy_pad, or __nonstring over strncpy (see: https://github.com/KSPP/linux/issues/90) In synth_field_string_size(), replace strncpy() with memcpy() to copy 'len' characters from 'start' to 'buf'. The code manually adds a NUL terminator after the copy, making memcpy safe here. Link: https://lore.kernel.org/20250325181232.38284-1-siddarthsgml@gmail.com Signed-off-by: Siddarth G Signed-off-by: Steven Rostedt (Google)

tracing: Fix synth event printk format for str fields

2025-03-25T21:42:38Z

The printk format for synth event uses "%.*s" to print string fields, but then only passes the pointer part as var arg. Replace %.*s with %s as the C string is guaranteed to be null-terminated. The output in print fmt should never have been updated as __get_str() handles the string limit because it can access the length of the string in the string meta data that is saved in the ring buffer. Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Fixes: 8db4d6bfbbf92 ("tracing: Change synthetic event string format to limit printed length") Link: https://lore.kernel.org/20250325165202.541088-1-douglas.raillard@arm.com Signed-off-by: Douglas Raillard Signed-off-by: Steven Rostedt (Google)

tracing: Do not use PERF enums when perf is not defined

2025-03-24T21:12:33Z

An update was made to up the module ref count when a synthetic event is registered for both trace and perf events. But if perf is not configured in, the perf enums used will cause the kernel to fail to build. Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Cc: Douglas Raillard Link: https://lore.kernel.org/20250323152151.528b5ced@batman.local.home Fixes: 21581dd4e7ff ("tracing: Ensure module defining synth event cannot be unloaded while tracing") Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202503232230.TeREVy8R-lkp@intel.com/ Signed-off-by: Steven Rostedt (Google)

tracing: Ensure module defining synth event cannot be unloaded while tracing

2025-03-23T12:34:31Z

Currently, using synth_event_delete() will fail if the event is being used (tracing in progress), but that is normally done in the module exit function. At that stage, failing is problematic as returning a non-zero status means the module will become locked (impossible to unload or reload again). Instead, ensure the module exit function does not get called in the first place by increasing the module refcnt when the event is enabled. Cc: stable@vger.kernel.org Cc: Mathieu Desnoyers Fixes: 35ca5207c2d11 ("tracing: Add synthetic event command generation functions") Link: https://lore.kernel.org/20250318180906.226841-1-douglas.raillard@arm.com Signed-off-by: Douglas Raillard Acked-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google)

tracing: Align synth event print fmt

2025-03-23T12:34:31Z

The vast majority of ftrace event print fmt consist of a space-separated field=value pair. Synthetic event currently use a comma-separated field=value pair, which sticks out from events created via more classical means. Align the format of synth events so they look just like any other event, for better consistency and less headache when doing crude text-based data processing. Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Link: https://lore.kernel.org/20250319215028.1680278-1-douglas.raillard@arm.com Signed-off-by: Douglas Raillard Signed-off-by: Steven Rostedt (Google)

tracing: Switch trace_events_synth.c code over to use guard()

2024-12-26T15:38:37Z

There are a couple functions in trace_events_synth.c that have "goto out" or equivalent on error in order to release locks that were taken. This can be error prone or just simply make the code more complex. Switch every location that ends with unlocking a mutex on error over to using the guard(mutex)() infrastructure to let the compiler worry about releasing locks. This makes the code easier to read and understand. Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Cc: Peter Zijlstra Link: https://lore.kernel.org/20241219201346.371082515@goodmis.org Signed-off-by: Steven Rostedt (Google)

tracing/synthetic: Fix trace_string() return value

2024-02-15T16:40:01Z

Fix trace_string() by assigning the string length to the return variable which got lost in commit ddeea494a16f ("tracing/synthetic: Use union instead of casts") and caused trace_string() to always return 0. Link: https://lore.kernel.org/linux-trace-kernel/20240214220555.711598-1-thorsten.blum@toblux.com Cc: stable@vger.kernel.org Cc: Mathieu Desnoyers Fixes: ddeea494a16f ("tracing/synthetic: Use union instead of casts") Acked-by: Masami Hiramatsu (Google) Signed-off-by: Thorsten Blum Signed-off-by: Steven Rostedt (Google)

tracing/synthetic: fix kernel-doc warnings

2023-12-20T17:51:03Z

scripts/kernel-doc warns about using @args: for variadic arguments to functions. Documentation/doc-guide/kernel-doc.rst says that this should be written as @...: instead, so update the source code to match that, preventing the warnings. trace_events_synth.c:1165: warning: Excess function parameter 'args' description in '__synth_event_gen_cmd_start' trace_events_synth.c:1714: warning: Excess function parameter 'args' description in 'synth_event_trace' Link: https://lore.kernel.org/linux-trace-kernel/20231220061226.30962-1-rdunlap@infradead.org Cc: Mathieu Desnoyers Fixes: 35ca5207c2d11 ("tracing: Add synthetic event command generation functions") Fixes: 8dcc53ad956d2 ("tracing: Add synth_event_trace() and related functions") Acked-by: Masami Hiramatsu (Google) Signed-off-by: Randy Dunlap Signed-off-by: Steven Rostedt (Google)