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If a perf trace event selector specifies a maximum number of events to output
(i.e., "/nr=N/" syntax), the event printing handler, trace__event_handler,
disables the event selector after the maximum number events are
printed.
Furthermore, trace__event_handler checked if the event selector was
disabled before doing any work. This avoided exceeding the maximum
number of events to print if more events were in the buffer before the
selector was disabled.
However, the event selector can be disabled for reasons other than
exceeding the maximum number of events. In particular, when the traced
subprocess exits, the main loop disables all event selectors. This meant
the last events of a traced subprocess might be lost to the printing
handler's short-circuiting logic.
This nondeterministic problem could be seen by running the following many times:
$ perf trace -e syscalls:sys_enter_exit_group true
trace__event_handler should simply check for exceeding the maximum number of
events to print rather than the state of the event selector.
Fixes: a9c5e6c1e9 ("perf trace: Introduce per-event maximum number of events property")
Signed-off-by: Benjamin Peterson <benjamin@engflow.com>
Tested-by: Howard Chu <howardchu95@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241107232128.108981-1-benjamin@engflow.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.