This is a note to let you know that I've just added the patch titled
tracing/synthetic: Skip first entry for stack traces
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tracing-synthetic-skip-first-entry-for-stack-traces.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 393bd346d98c07c4fa2a93d707ae8fa51979942b
Author: Sven Schnelle <svens@xxxxxxxxxxxxx>
Date: Wed Aug 16 17:49:27 2023 +0200
tracing/synthetic: Skip first entry for stack traces
[ Upstream commit 887f92e09ef34a949745ad26ce82be69e2dabcf6 ]
While debugging another issue I noticed that the stack trace output
contains the number of entries on top:
<idle>-0 [000] d..4. 203.322502: wake_lat: pid=0 delta=2268270616 stack=STACK:
=> 0x10
=> __schedule+0xac6/0x1a98
=> schedule+0x126/0x2c0
=> schedule_timeout+0x242/0x2c0
=> __wait_for_common+0x434/0x680
=> __wait_rcu_gp+0x198/0x3e0
=> synchronize_rcu+0x112/0x138
=> ring_buffer_reset_online_cpus+0x140/0x2e0
=> tracing_reset_online_cpus+0x15c/0x1d0
=> tracing_set_clock+0x180/0x1d8
=> hist_register_trigger+0x486/0x670
=> event_hist_trigger_parse+0x494/0x1318
=> trigger_process_regex+0x1d4/0x258
=> event_trigger_write+0xb4/0x170
=> vfs_write+0x210/0xad0
=> ksys_write+0x122/0x208
Fix this by skipping the first element. Also replace the pointer
logic with an index variable which is easier to read.
Link: https://lkml.kernel.org/r/20230816154928.4171614-3-svens@xxxxxxxxxxxxx
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Fixes: 00cf3d672a9d ("tracing: Allow synthetic events to pass around stacktraces")
Signed-off-by: Sven Schnelle <svens@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index da0627fa91caf..a4c58a932dfa6 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -350,7 +350,7 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter,
struct trace_seq *s = &iter->seq;
struct synth_trace_event *entry;
struct synth_event *se;
- unsigned int i, n_u64;
+ unsigned int i, j, n_u64;
char print_fmt[32];
const char *fmt;
@@ -389,18 +389,13 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter,
n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
}
} else if (se->fields[i]->is_stack) {
- unsigned long *p, *end;
union trace_synth_field *data = &entry->fields[n_u64];
-
- p = (void *)entry + data->as_dynamic.offset;
- end = (void *)p + data->as_dynamic.len - (sizeof(long) - 1);
+ unsigned long *p = (void *)entry + data->as_dynamic.offset;
trace_seq_printf(s, "%s=STACK:\n", se->fields[i]->name);
-
- for (; *p && p < end; p++)
- trace_seq_printf(s, "=> %pS\n", (void *)*p);
+ for (j = 1; j < data->as_dynamic.len / sizeof(long); j++)
+ trace_seq_printf(s, "=> %pS\n", (void *)p[j]);
n_u64++;
-
} else {
struct trace_print_flags __flags[] = {
__def_gfpflag_names, {-1, NULL} };
@@ -490,10 +485,6 @@ static unsigned int trace_stack(struct synth_trace_event *entry,
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. */
