From 00cf3d672a9dd409418647e9f98784c339c3ff63 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Google)" Date: Tue, 17 Jan 2023 10:21:28 -0500 Subject: tracing: Allow synthetic events to pass around stacktraces Allow a stacktrace from one event to be displayed by the end event of a synthetic event. This is very useful when looking for the longest latency of a sleep or something blocked on I/O. # cd /sys/kernel/tracing/ # echo 's:block_lat pid_t pid; u64 delta; unsigned long[] stack;' > dynamic_events # echo 'hist:keys=next_pid:ts=common_timestamp.usecs,st=stacktrace if prev_state == 1||prev_state == 2' > events/sched/sched_switch/trigger # echo 'hist:keys=prev_pid:delta=common_timestamp.usecs-$ts,s=$st:onmax($delta).trace(block_lat,prev_pid,$delta,$s)' >> events/sched/sched_switch/trigger The above creates a "block_lat" synthetic event that take the stacktrace of when a task schedules out in either the interruptible or uninterruptible states, and on a new per process max $delta (the time it was scheduled out), will print the process id and the stacktrace. # echo 1 > events/synthetic/block_lat/enable # cat trace # TASK-PID CPU# ||||| TIMESTAMP FUNCTION # | | | ||||| | | kworker/u16:0-767 [006] d..4. 560.645045: block_lat: pid=767 delta=66 stack=STACK: => __schedule => schedule => pipe_read => vfs_read => ksys_read => do_syscall_64 => 0x966000aa -0 [003] d..4. 561.132117: block_lat: pid=0 delta=413787 stack=STACK: => __schedule => schedule => schedule_hrtimeout_range_clock => do_sys_poll => __x64_sys_poll => do_syscall_64 => 0x966000aa <...>-153 [006] d..4. 562.068407: block_lat: pid=153 delta=54 stack=STACK: => __schedule => schedule => io_schedule => rq_qos_wait => wbt_wait => __rq_qos_throttle => blk_mq_submit_bio => submit_bio_noacct_nocheck => ext4_bio_write_page => mpage_submit_page => mpage_process_page_bufs => mpage_prepare_extent_to_map => ext4_do_writepages => ext4_writepages => do_writepages => __writeback_single_inode Link: https://lkml.kernel.org/r/20230117152236.010941267@goodmis.org Cc: Masami Hiramatsu Cc: Andrew Morton Cc: Tom Zanussi Cc: Ross Zwisler Cc: Ching-lin Yu Signed-off-by: Steven Rostedt (Google) --- kernel/trace/trace_events_synth.c | 80 ++++++++++++++++++++++++++++++++++++++- 1 file changed, 79 insertions(+), 1 deletion(-) (limited to 'kernel/trace/trace_events_synth.c') diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c index 9f79cd689b79..adb630633f31 100644 --- a/kernel/trace/trace_events_synth.c +++ b/kernel/trace/trace_events_synth.c @@ -173,6 +173,14 @@ static int synth_field_is_string(char *type) return false; } +static int synth_field_is_stack(char *type) +{ + if (strstr(type, "long[") != NULL) + return true; + + return false; +} + static int synth_field_string_size(char *type) { char buf[4], *end, *start; @@ -248,6 +256,8 @@ static int synth_field_size(char *type) size = sizeof(gfp_t); else if (synth_field_is_string(type)) size = synth_field_string_size(type); + else if (synth_field_is_stack(type)) + size = 0; return size; } @@ -292,6 +302,8 @@ static const char *synth_field_fmt(char *type) fmt = "%x"; else if (synth_field_is_string(type)) fmt = "%.*s"; + else if (synth_field_is_stack(type)) + fmt = "%s"; return fmt; } @@ -371,6 +383,23 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter, i == se->n_fields - 1 ? "" : " "); n_u64 += STR_VAR_LEN_MAX / sizeof(u64); } + } else if (se->fields[i]->is_stack) { + u32 offset, data_offset, len; + unsigned long *p, *end; + + offset = (u32)entry->fields[n_u64]; + data_offset = offset & 0xffff; + len = offset >> 16; + + p = (void *)entry + data_offset; + end = (void *)p + len - (sizeof(long) - 1); + + trace_seq_printf(s, "%s=STACK:\n", se->fields[i]->name); + + for (; *p && p < end; p++) + trace_seq_printf(s, "=> %pS\n", (void *)*p); + n_u64++; + } else { struct trace_print_flags __flags[] = { __def_gfpflag_names, {-1, NULL} }; @@ -446,6 +475,43 @@ static unsigned int trace_string(struct synth_trace_event *entry, return len; } +static unsigned int trace_stack(struct synth_trace_event *entry, + struct synth_event *event, + long *stack, + unsigned int data_size, + unsigned int *n_u64) +{ + unsigned int len; + u32 data_offset; + void *data_loc; + + data_offset = struct_size(entry, fields, event->n_u64); + data_offset += data_size; + + for (len = 0; len < HIST_STACKTRACE_DEPTH; len++) { + if (!stack[len]) + break; + } + + /* Include the zero'd element if it fits */ + if (len < HIST_STACKTRACE_DEPTH) + len++; + + len *= sizeof(long); + + /* Find the dynamic section to copy the stack into. */ + data_loc = (void *)entry + data_offset; + memcpy(data_loc, stack, len); + + /* Fill in the field that holds the offset/len combo */ + data_offset |= len << 16; + *(u32 *)&entry->fields[*n_u64] = data_offset; + + (*n_u64)++; + + return len; +} + static notrace void trace_event_raw_event_synth(void *__data, u64 *var_ref_vals, unsigned int *var_ref_idx) @@ -498,6 +564,12 @@ static notrace void trace_event_raw_event_synth(void *__data, event->fields[i]->is_dynamic, data_size, &n_u64); data_size += len; /* only dynamic string increments */ + } if (event->fields[i]->is_stack) { + long *stack = (long *)(long)var_ref_vals[val_idx]; + + len = trace_stack(entry, event, stack, + data_size, &n_u64); + data_size += len; } else { struct synth_field *field = event->fields[i]; u64 val = var_ref_vals[val_idx]; @@ -560,6 +632,9 @@ static int __set_synth_event_print_fmt(struct synth_event *event, event->fields[i]->is_dynamic) pos += snprintf(buf + pos, LEN_OR_ZERO, ", __get_str(%s)", event->fields[i]->name); + else if (event->fields[i]->is_stack) + pos += snprintf(buf + pos, LEN_OR_ZERO, + ", __get_stacktrace(%s)", event->fields[i]->name); else pos += snprintf(buf + pos, LEN_OR_ZERO, ", REC->%s", event->fields[i]->name); @@ -696,7 +771,8 @@ static struct synth_field *parse_synth_field(int argc, char **argv, ret = -EINVAL; goto free; } else if (size == 0) { - if (synth_field_is_string(field->type)) { + if (synth_field_is_string(field->type) || + synth_field_is_stack(field->type)) { char *type; len = sizeof("__data_loc ") + strlen(field->type) + 1; @@ -727,6 +803,8 @@ static struct synth_field *parse_synth_field(int argc, char **argv, if (synth_field_is_string(field->type)) field->is_string = true; + else if (synth_field_is_stack(field->type)) + field->is_stack = true; field->is_signed = synth_field_signed(field->type); out: -- cgit