| Message ID | 20250115180055.2136815-1-costa.shul@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v4] tools/rtla: Add osnoise_trace_is_off() | expand |
On Wed, Jan 15, 2025 at 07:58:30PM +0200, Costa Shulyupin wrote: > The original code accidentally works because offset of > `record->trace` is zero. It doesn't "accidentally work". The people who write this kind of code 100% understand what they are doing. They don't see it as anything complicated. regards, dan carpenter
On Wed, 15 Jan 2025 21:40:40 +0300 Dan Carpenter <dan.carpenter@linaro.org> wrote: > On Wed, Jan 15, 2025 at 07:58:30PM +0200, Costa Shulyupin wrote: > > The original code accidentally works because offset of > > `record->trace` is zero. > > It doesn't "accidentally work". The people who write this kind of > code 100% understand what they are doing. They don't see it as > anything complicated. I'm taking this patch but I replaced the change log with the following text: tools/rtla: Add osnoise_trace_is_off() All of the users of trace_is_off() passes in &record->trace as the second parameter, where record is a pointer to a struct osnoise_tool. This record could be NULL and there is a hidden dependency that the trace field is the first field to allow &record->trace to work with a NULL record pointer. In order to make this code a bit more robust, as record shouldn't be dereferenced if it is NULL, even if the code does work, create a new function called osnoise_trace_is_off() that takes the pointer to a struct osnoise_tool as its second parameter. This way it can properly test if it is NULL before it dereferences it. The old function trace_is_off() is removed and the function osnoise_trace_is_off() is added into osnoise.c which is what the struct osnoise_tool is associated with. -- Steve
On Thu, Jan 16, 2025 at 07:34:32PM -0500, Steven Rostedt wrote: > On Wed, 15 Jan 2025 21:40:40 +0300 > Dan Carpenter <dan.carpenter@linaro.org> wrote: > > > On Wed, Jan 15, 2025 at 07:58:30PM +0200, Costa Shulyupin wrote: > > > The original code accidentally works because offset of > > > `record->trace` is zero. > > > > It doesn't "accidentally work". The people who write this kind of > > code 100% understand what they are doing. They don't see it as > > anything complicated. > > I'm taking this patch but I replaced the change log with the following text: > > tools/rtla: Add osnoise_trace_is_off() > > All of the users of trace_is_off() passes in &record->trace as the second > parameter, where record is a pointer to a struct osnoise_tool. This record > could be NULL and there is a hidden dependency that the trace field is the > first field to allow &record->trace to work with a NULL record pointer. > > In order to make this code a bit more robust, as record shouldn't be > dereferenced if it is NULL, even if the code does work, create a new > function called osnoise_trace_is_off() that takes the pointer to a > struct osnoise_tool as its second parameter. This way it can properly test > if it is NULL before it dereferences it. > > The old function trace_is_off() is removed and the function > osnoise_trace_is_off() is added into osnoise.c which is what the > struct osnoise_tool is associated with. Thanks! regards, dan carpenter
diff --git a/tools/tracing/rtla/src/osnoise.c b/tools/tracing/rtla/src/osnoise.c index 245e9344932bc..fcfaaff6ea164 100644 --- a/tools/tracing/rtla/src/osnoise.c +++ b/tools/tracing/rtla/src/osnoise.c @@ -1079,6 +1079,22 @@ struct osnoise_tool *osnoise_init_trace_tool(char *tracer) return NULL; } +bool osnoise_trace_is_off(struct osnoise_tool *tool, struct osnoise_tool *record) +{ + /* + * The tool instance is always present, it is the one used to collect + * data. + */ + if (!tracefs_trace_is_on(tool->trace.inst)) + return true; + + /* + * The trace record instance is only enabled when -t is set. IOW, when the system + * is tracing. + */ + return record && !tracefs_trace_is_on(record->trace.inst); +} + static void osnoise_usage(int err) { int i; diff --git a/tools/tracing/rtla/src/osnoise.h b/tools/tracing/rtla/src/osnoise.h index 555f4f4903cc2..1dc188baddef9 100644 --- a/tools/tracing/rtla/src/osnoise.h +++ b/tools/tracing/rtla/src/osnoise.h @@ -104,6 +104,7 @@ struct osnoise_tool { void osnoise_destroy_tool(struct osnoise_tool *top); struct osnoise_tool *osnoise_init_tool(char *tool_name); struct osnoise_tool *osnoise_init_trace_tool(char *tracer); +bool osnoise_trace_is_off(struct osnoise_tool *tool, struct osnoise_tool *record); int osnoise_hist_main(int argc, char *argv[]); int osnoise_top_main(int argc, char **argv); diff --git a/tools/tracing/rtla/src/osnoise_hist.c b/tools/tracing/rtla/src/osnoise_hist.c index 214e2c93fde01..f250f999a4eee 100644 --- a/tools/tracing/rtla/src/osnoise_hist.c +++ b/tools/tracing/rtla/src/osnoise_hist.c @@ -970,7 +970,7 @@ int osnoise_hist_main(int argc, char *argv[]) goto out_hist; } - if (trace_is_off(&tool->trace, &record->trace)) + if (osnoise_trace_is_off(tool, record)) break; } @@ -980,7 +980,7 @@ int osnoise_hist_main(int argc, char *argv[]) return_value = 0; - if (trace_is_off(&tool->trace, &record->trace)) { + if (osnoise_trace_is_off(tool, record)) { printf("rtla osnoise hit stop tracing\n"); if (params->trace_output) { printf(" Saving trace to %s\n", params->trace_output); diff --git a/tools/tracing/rtla/src/osnoise_top.c b/tools/tracing/rtla/src/osnoise_top.c index 45647495ce3bd..6d50653ae224c 100644 --- a/tools/tracing/rtla/src/osnoise_top.c +++ b/tools/tracing/rtla/src/osnoise_top.c @@ -801,7 +801,7 @@ int osnoise_top_main(int argc, char **argv) if (!params->quiet) osnoise_print_stats(params, tool); - if (trace_is_off(&tool->trace, &record->trace)) + if (osnoise_trace_is_off(tool, record)) break; } @@ -810,7 +810,7 @@ int osnoise_top_main(int argc, char **argv) return_value = 0; - if (trace_is_off(&tool->trace, &record->trace)) { + if (osnoise_trace_is_off(tool, record)) { printf("osnoise hit stop tracing\n"); if (params->trace_output) { printf(" Saving trace to %s\n", params->trace_output); diff --git a/tools/tracing/rtla/src/timerlat_hist.c b/tools/tracing/rtla/src/timerlat_hist.c index 4403cc4eba302..ddb833ce89d01 100644 --- a/tools/tracing/rtla/src/timerlat_hist.c +++ b/tools/tracing/rtla/src/timerlat_hist.c @@ -1342,7 +1342,7 @@ int timerlat_hist_main(int argc, char *argv[]) goto out_hist; } - if (trace_is_off(&tool->trace, &record->trace)) + if (osnoise_trace_is_off(tool, record)) break; /* is there still any user-threads ? */ @@ -1363,7 +1363,7 @@ int timerlat_hist_main(int argc, char *argv[]) return_value = 0; - if (trace_is_off(&tool->trace, &record->trace)) { + if (osnoise_trace_is_off(tool, record)) { printf("rtla timerlat hit stop tracing\n"); if (!params->no_aa) diff --git a/tools/tracing/rtla/src/timerlat_top.c b/tools/tracing/rtla/src/timerlat_top.c index 059b468981e4d..9a707c42bb1ac 100644 --- a/tools/tracing/rtla/src/timerlat_top.c +++ b/tools/tracing/rtla/src/timerlat_top.c @@ -1093,7 +1093,7 @@ int timerlat_top_main(int argc, char *argv[]) while (!stop_tracing) { sleep(params->sleep_time); - if (params->aa_only && !trace_is_off(&top->trace, &record->trace)) + if (params->aa_only && !osnoise_trace_is_off(top, record)) continue; retval = tracefs_iterate_raw_events(trace->tep, @@ -1110,7 +1110,7 @@ int timerlat_top_main(int argc, char *argv[]) if (!params->quiet) timerlat_print_stats(params, top); - if (trace_is_off(&top->trace, &record->trace)) + if (osnoise_trace_is_off(top, record)) break; /* is there still any user-threads ? */ @@ -1131,7 +1131,7 @@ int timerlat_top_main(int argc, char *argv[]) return_value = 0; - if (trace_is_off(&top->trace, &record->trace)) { + if (osnoise_trace_is_off(top, record)) { printf("rtla timerlat hit stop tracing\n"); if (!params->no_aa) diff --git a/tools/tracing/rtla/src/trace.c b/tools/tracing/rtla/src/trace.c index 170a706248abf..6e24649857dd8 100644 --- a/tools/tracing/rtla/src/trace.c +++ b/tools/tracing/rtla/src/trace.c @@ -522,25 +522,6 @@ void trace_events_destroy(struct trace_instance *instance, trace_events_free(events); } -int trace_is_off(struct trace_instance *tool, struct trace_instance *trace) -{ - /* - * The tool instance is always present, it is the one used to collect - * data. - */ - if (!tracefs_trace_is_on(tool->inst)) - return 1; - - /* - * The trace instance is only enabled when -t is set. IOW, when the system - * is tracing. - */ - if (trace && !tracefs_trace_is_on(trace->inst)) - return 1; - - return 0; -} - /* * trace_set_buffer_size - set the per-cpu tracing buffer size. */ diff --git a/tools/tracing/rtla/src/trace.h b/tools/tracing/rtla/src/trace.h index c7c92dc9a18a6..1ddb51cdaf97c 100644 --- a/tools/tracing/rtla/src/trace.h +++ b/tools/tracing/rtla/src/trace.h @@ -47,5 +47,4 @@ int trace_events_enable(struct trace_instance *instance, int trace_event_add_filter(struct trace_events *event, char *filter); int trace_event_add_trigger(struct trace_events *event, char *trigger); -int trace_is_off(struct trace_instance *tool, struct trace_instance *trace); int trace_set_buffer_size(struct trace_instance *trace, int size);
The usage of trace_is_off() confusing, which requires a detailed explanation. Let's modify the source code by moving the first member, `trace`, of the `osnoise_tool` structure to the second position: struct osnoise_tool { - struct trace_instance trace; struct osnoise_context *context; + struct trace_instance trace; A correct program would work properly after this change, but this one does not. Then, run the program under gdb to observe the behavior. gdb -q --args ./rtla osnoise -D -d 2 -T 10000 -q Program received signal SIGSEGV, Segmentation fault. 0x000000000040298f in trace_is_off (tool=tool@entry=0x418458, trace=trace@entry=0x8) at src/trace.c:538 538 if (trace && !tracefs_trace_is_on(trace->inst)) ... The program checks if trace, which has a value of 8, is not null, and then crashes when it attempts to dereference trace->inst. It happens because trace_is_off() is called as: trace_is_off(&tool->trace, &record->trace) Where `record` is NULL. Expression `&record->trace` returns offset of member `trace`, which is 8. The original code accidentally works because offset of `record->trace` is zero. Expanded wrong instructions are: record = NULL; if (&record->trace && !tracefs_trace_is_on(record->trace.inst)) return 1; The correct instructions are: record = NULL; if (record && !tracefs_trace_is_on(record->trace.inst)) return 1; Refactor `trace_is_off` to `osnoise_trace_is_off` and move it to osnoise.c because it instead of `struct trace_instance` accesses `struct osnoise_tool`, which is out of the scope of trace.c. Signed-off-by: Costa Shulyupin <costa.shul@redhat.com> --- v4: - Add prefix to the subject v3: - Dot't call a bug - return boolean expression v2: - Refactor trace_is_off() to osnoise_trace_is_off() - Write detailed explanation Signed-off-by: Costa Shulyupin <costa.shul@redhat.com> --- tools/tracing/rtla/src/osnoise.c | 16 ++++++++++++++++ tools/tracing/rtla/src/osnoise.h | 1 + tools/tracing/rtla/src/osnoise_hist.c | 4 ++-- tools/tracing/rtla/src/osnoise_top.c | 4 ++-- tools/tracing/rtla/src/timerlat_hist.c | 4 ++-- tools/tracing/rtla/src/timerlat_top.c | 6 +++--- tools/tracing/rtla/src/trace.c | 19 ------------------- tools/tracing/rtla/src/trace.h | 1 - 8 files changed, 26 insertions(+), 29 deletions(-)