| Message ID | 1ed6906cd9d6477ef2bd8e63c61de20a9ffe64d7.1676063532.git.zanussi@kernel.org (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | fc1a9dc101292403babe0c5c2f99f4748580ed98 |
| Headers | show |
| Series | tracing/histogram: Some fixes for new stacktrace variables | expand |
On Fri, 10 Feb 2023 15:33:03 -0600 Tom Zanussi <zanussi@kernel.org> wrote: > Because stacktraces are saved in dynamic strings, > trace_event_raw_event_synth() uses strlen to determine the length of > the stack. Stacktraces may contain 0-bytes, though, in the saved > addresses, so the length found and passed to reserve() will be too > small. Good catch! > > Fix this by using the first unsigned long in the stack variables to > store the actual number of elements in the stack and have > trace_event_raw_event_synth() use that to determine the length of the > stack. > > Signed-off-by: Tom Zanussi <zanussi@kernel.org> > --- > kernel/trace/trace_events_hist.c | 12 ++++++++---- > kernel/trace/trace_events_synth.c | 7 ++++++- > 2 files changed, 14 insertions(+), 5 deletions(-) > > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c > index 888b7a394ce5..76bd105988c6 100644 > --- a/kernel/trace/trace_events_hist.c > +++ b/kernel/trace/trace_events_hist.c > @@ -3135,13 +3135,15 @@ static inline void __update_field_vars(struct tracing_map_elt *elt, > size = min(val->size, STR_VAR_LEN_MAX); > strscpy(str, val_str, size); > } else { > + char *stack_start = str + sizeof(unsigned long); > int e; > > - e = stack_trace_save((void *)str, > + e = stack_trace_save((void *)stack_start, > HIST_STACKTRACE_DEPTH, > HIST_STACKTRACE_SKIP); BTW, the size of "str" is enough to store HIST_STACKTRACE_DEPTH? In string case, size = min(val->size, STR_VAR_LEN_MAX); will limit the max size. Thank you, > if (e < HIST_STACKTRACE_DEPTH - 1) > - ((unsigned long *)str)[e] = 0; > + ((unsigned long *)stack_start)[e] = 0; > + *((unsigned long *)str) = e; > } > var_val = (u64)(uintptr_t)str; > } > @@ -5133,13 +5135,15 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data, > size = min(hist_field->size, STR_VAR_LEN_MAX); > strscpy(str, val_str, size); > } else { > + char *stack_start = str + sizeof(unsigned long); > int e; > > - e = stack_trace_save((void *)str, > + e = stack_trace_save((void *)stack_start, > HIST_STACKTRACE_DEPTH, > HIST_STACKTRACE_SKIP); > if (e < HIST_STACKTRACE_DEPTH - 1) > - ((unsigned long *)str)[e] = 0; > + ((unsigned long *)stack_start)[e] = 0; > + *((unsigned long *)str) = e; > } > hist_val = (u64)(uintptr_t)str; > } > diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c > index d458d7a0dfd7..6209b23c863f 100644 > --- a/kernel/trace/trace_events_synth.c > +++ b/kernel/trace/trace_events_synth.c > @@ -538,7 +538,12 @@ static notrace void trace_event_raw_event_synth(void *__data, > val_idx = var_ref_idx[field_pos]; > str_val = (char *)(long)var_ref_vals[val_idx]; > > - len = kern_fetch_store_strlen((unsigned long)str_val); > + if (event->dynamic_fields[i]->is_stack) { > + len = *((unsigned long *)str_val); > + len *= sizeof(unsigned long); > + } else { > + len = kern_fetch_store_strlen((unsigned long)str_val); > + } > > fields_size += len; > } > -- > 2.34.1 >
On Tue, 14 Feb 2023 00:24:18 +0900 Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote: > > - e = stack_trace_save((void *)str, > > + e = stack_trace_save((void *)stack_start, > > HIST_STACKTRACE_DEPTH, > > HIST_STACKTRACE_SKIP); > > BTW, the size of "str" is enough to store HIST_STACKTRACE_DEPTH? > In string case, > > size = min(val->size, STR_VAR_LEN_MAX); > > will limit the max size. Well, we have: #define HIST_STACKTRACE_DEPTH 16 And 16 * 8 = 128 #define STR_VAR_LEN_MAX MAX_FILTER_STR_VAL #define MAX_FILTER_STR_VAL 256U So 128 < 256, with plenty of room. I wouldn't do this runtime, but we should add here: BUILD_BUG_ON((HIST_STACKTRACE_DEPTH + 1) * sizeof(long) >= STR_VAR_LEN_MAX); -- Steve
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 888b7a394ce5..76bd105988c6 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -3135,13 +3135,15 @@ static inline void __update_field_vars(struct tracing_map_elt *elt, size = min(val->size, STR_VAR_LEN_MAX); strscpy(str, val_str, size); } else { + char *stack_start = str + sizeof(unsigned long); int e; - e = stack_trace_save((void *)str, + e = stack_trace_save((void *)stack_start, HIST_STACKTRACE_DEPTH, HIST_STACKTRACE_SKIP); if (e < HIST_STACKTRACE_DEPTH - 1) - ((unsigned long *)str)[e] = 0; + ((unsigned long *)stack_start)[e] = 0; + *((unsigned long *)str) = e; } var_val = (u64)(uintptr_t)str; } @@ -5133,13 +5135,15 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data, size = min(hist_field->size, STR_VAR_LEN_MAX); strscpy(str, val_str, size); } else { + char *stack_start = str + sizeof(unsigned long); int e; - e = stack_trace_save((void *)str, + e = stack_trace_save((void *)stack_start, HIST_STACKTRACE_DEPTH, HIST_STACKTRACE_SKIP); if (e < HIST_STACKTRACE_DEPTH - 1) - ((unsigned long *)str)[e] = 0; + ((unsigned long *)stack_start)[e] = 0; + *((unsigned long *)str) = e; } hist_val = (u64)(uintptr_t)str; } diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c index d458d7a0dfd7..6209b23c863f 100644 --- a/kernel/trace/trace_events_synth.c +++ b/kernel/trace/trace_events_synth.c @@ -538,7 +538,12 @@ static notrace void trace_event_raw_event_synth(void *__data, val_idx = var_ref_idx[field_pos]; str_val = (char *)(long)var_ref_vals[val_idx]; - len = kern_fetch_store_strlen((unsigned long)str_val); + if (event->dynamic_fields[i]->is_stack) { + len = *((unsigned long *)str_val); + len *= sizeof(unsigned long); + } else { + len = kern_fetch_store_strlen((unsigned long)str_val); + } fields_size += len; }
Because stacktraces are saved in dynamic strings, trace_event_raw_event_synth() uses strlen to determine the length of the stack. Stacktraces may contain 0-bytes, though, in the saved addresses, so the length found and passed to reserve() will be too small. Fix this by using the first unsigned long in the stack variables to store the actual number of elements in the stack and have trace_event_raw_event_synth() use that to determine the length of the stack. Signed-off-by: Tom Zanussi <zanussi@kernel.org> --- kernel/trace/trace_events_hist.c | 12 ++++++++---- kernel/trace/trace_events_synth.c | 7 ++++++- 2 files changed, 14 insertions(+), 5 deletions(-)