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tracing: Allow synthetic events to pass around stacktraces 

[ Upstream commit 00cf3d672a ]

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

           <idle>-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 <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Ross Zwisler <zwisler@google.com>
Cc: Ching-lin Yu <chinglinyu@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Stable-dep-of: 797311bce5 ("tracing/probes: Fix to record 0-length data_loc in fetch_store_string*() if fails")
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Steven Rostedt (Google) 2023-01-17 10:21:28 -05:00 committed by Greg Kroah-Hartman
parent e7b4d24fa0
commit 5f52389bdd
4 changed files with 87 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
kernel/trace/trace.h
View File

@ -113,6 +113,10 @@ enum trace_type {
#define MEM_FAIL(condition, fmt, ...) \
DO_ONCE_LITE_IF(condition, pr_err, "ERROR: " fmt, ##__VA_ARGS__)
#define HIST_STACKTRACE_DEPTH 16
#define HIST_STACKTRACE_SIZE (HIST_STACKTRACE_DEPTH * sizeof(unsigned long))
#define HIST_STACKTRACE_SKIP 5
/*
* syscalls are special, and need special handling, this is why
* they are not included in trace_entries.h

7
kernel/trace/trace_events_hist.c
View File

@ -315,10 +315,6 @@ DEFINE_HIST_FIELD_FN(u8);
#define for_each_hist_key_field(i, hist_data) \
for ((i) = (hist_data)->n_vals; (i) < (hist_data)->n_fields; (i)++)
#define HIST_STACKTRACE_DEPTH 16
#define HIST_STACKTRACE_SIZE (HIST_STACKTRACE_DEPTH * sizeof(unsigned long))
#define HIST_STACKTRACE_SKIP 5
#define HITCOUNT_IDX 0
#define HIST_KEY_SIZE_MAX (MAX_FILTER_STR_VAL + HIST_STACKTRACE_SIZE)
@ -3431,6 +3427,9 @@ static int check_synth_field(struct synth_event *event,
&& field->is_dynamic)
return 0;
if (strstr(hist_field->type, "long[") && field->is_stack)
return 0;
if (strcmp(field->type, hist_field->type) != 0) {
if (field->size != hist_field->size ||
(!field->is_string && field->is_signed != hist_field->is_signed))

80
kernel/trace/trace_events_synth.c
View File

@ -165,6 +165,14 @@ 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;
@ -240,6 +248,8 @@ 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;
}
@ -284,6 +294,8 @@ 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;
}
@ -363,6 +375,23 @@ 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} };
@ -439,6 +468,43 @@ 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)
@ -491,6 +557,12 @@ 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];
@ -553,6 +625,9 @@ 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);
@ -689,7 +764,8 @@ 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;
@ -720,6 +796,8 @@ 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:

1
kernel/trace/trace_synth.h
View File

@ -18,6 +18,7 @@ struct synth_field {
bool is_signed;
bool is_string;
bool is_dynamic;
bool is_stack;
};
struct synth_event {