FAILED: patch "[PATCH] tracing: Do not add length to print format in synthetic" failed to apply to 6.1-stable tree

FAILED: patch "[PATCH] tracing: Do not add length to print format in synthetic" failed to apply to 6.1-stable tree

[gregkh]

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x e1a453a57bc76be678bd746f84e3d73f378a9511
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025041706-ambiance-zen-5f4e@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e1a453a57bc76be678bd746f84e3d73f378a9511 Mon Sep 17 00:00:00 2001
From: Steven Rostedt <rostedt@goodmis.org>
Date: Mon, 7 Apr 2025 15:41:39 -0400
Subject: [PATCH] tracing: Do not add length to print format in synthetic
 events

The following causes a vsnprintf fault:

  # echo 's:wake_lat char[] wakee; u64 delta;' >> /sys/kernel/tracing/dynamic_events
  # echo 'hist:keys=pid:ts=common_timestamp.usecs if !(common_flags & 0x18)' > /sys/kernel/tracing/events/sched/sched_waking/trigger
  # echo 'hist:keys=next_pid:delta=common_timestamp.usecs-$ts:onmatch(sched.sched_waking).trace(wake_lat,next_comm,$delta)' > /sys/kernel/tracing/events/sched/sched_switch/trigger

Because the synthetic event's "wakee" field is created as a dynamic string
(even though the string copied is not). The print format to print the
dynamic string changed from "%*s" to "%s" because another location
(__set_synth_event_print_fmt()) exported this to user space, and user
space did not need that. But it is still used in print_synth_event(), and
the output looks like:

          <idle>-0       [001] d..5.   193.428167: wake_lat: wakee=(efault)sshd-sessiondelta=155
    sshd-session-879     [001] d..5.   193.811080: wake_lat: wakee=(efault)kworker/u34:5delta=58
          <idle>-0       [002] d..5.   193.811198: wake_lat: wakee=(efault)bashdelta=91
            bash-880     [002] d..5.   193.811371: wake_lat: wakee=(efault)kworker/u35:2delta=21
          <idle>-0       [001] d..5.   193.811516: wake_lat: wakee=(efault)sshd-sessiondelta=129
    sshd-session-879     [001] d..5.   193.967576: wake_lat: wakee=(efault)kworker/u34:5delta=50

The length isn't needed as the string is always nul terminated. Just print
the string and not add the length (which was hard coded to the max string
length anyway).

Cc: stable@vger.kernel.org
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Douglas Raillard <douglas.raillard@arm.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Link: https://lore.kernel.org/20250407154139.69955768@gandalf.local.home
Fixes: 4d38328eb442d ("tracing: Fix synth event printk format for str fields");
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index 969f48742d72..33cfbd4ed76d 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -370,7 +370,6 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter,
 				union trace_synth_field *data = &entry->fields[n_u64];
 
 				trace_seq_printf(s, print_fmt, se->fields[i]->name,
-						 STR_VAR_LEN_MAX,
 						 (char *)entry + data->as_dynamic.offset,
 						 i == se->n_fields - 1 ? "" : " ");
 				n_u64++;

[PATCH 6.1.y] tracing: Do not add length to print format in synthetic events

[Sasha Levin]

From: Steven Rostedt <rostedt@goodmis.org>

[ Upstream commit e1a453a57bc76be678bd746f84e3d73f378a9511 ]

The following causes a vsnprintf fault:

  # echo 's:wake_lat char[] wakee; u64 delta;' >> /sys/kernel/tracing/dynamic_events
  # echo 'hist:keys=pid:ts=common_timestamp.usecs if !(common_flags & 0x18)' > /sys/kernel/tracing/events/sched/sched_waking/trigger
  # echo 'hist:keys=next_pid:delta=common_timestamp.usecs-$ts:onmatch(sched.sched_waking).trace(wake_lat,next_comm,$delta)' > /sys/kernel/tracing/events/sched/sched_switch/trigger

Because the synthetic event's "wakee" field is created as a dynamic string
(even though the string copied is not). The print format to print the
dynamic string changed from "%*s" to "%s" because another location
(__set_synth_event_print_fmt()) exported this to user space, and user
space did not need that. But it is still used in print_synth_event(), and
the output looks like:

          <idle>-0       [001] d..5.   193.428167: wake_lat: wakee=(efault)sshd-sessiondelta=155
    sshd-session-879     [001] d..5.   193.811080: wake_lat: wakee=(efault)kworker/u34:5delta=58
          <idle>-0       [002] d..5.   193.811198: wake_lat: wakee=(efault)bashdelta=91
            bash-880     [002] d..5.   193.811371: wake_lat: wakee=(efault)kworker/u35:2delta=21
          <idle>-0       [001] d..5.   193.811516: wake_lat: wakee=(efault)sshd-sessiondelta=129
    sshd-session-879     [001] d..5.   193.967576: wake_lat: wakee=(efault)kworker/u34:5delta=50

The length isn't needed as the string is always nul terminated. Just print
the string and not add the length (which was hard coded to the max string
length anyway).

Cc: stable@vger.kernel.org
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Douglas Raillard <douglas.raillard@arm.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Link: https://lore.kernel.org/20250407154139.69955768@gandalf.local.home
Fixes: 4d38328eb442d ("tracing: Fix synth event printk format for str fields");
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
[ offset calculations instead of union-based data structures ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/trace_events_synth.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index 385e9fbbfbe7c..c2817d0c05b69 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -383,13 +383,11 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter,
 				str_field = (char *)entry + data_offset;
 
 				trace_seq_printf(s, print_fmt, se->fields[i]->name,
-						 STR_VAR_LEN_MAX,
 						 str_field,
 						 i == se->n_fields - 1 ? "" : " ");
 				n_u64++;
 			} else {
 				trace_seq_printf(s, print_fmt, se->fields[i]->name,
-						 STR_VAR_LEN_MAX,
 						 (char *)&entry->fields[n_u64],
 						 i == se->n_fields - 1 ? "" : " ");
 				n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
-- 
2.51.0

Re: [PATCH 6.1.y] tracing: Do not add length to print format in synthetic events

[Douglas Raillard]

Hi Sasha,

On 07-09-2025 23:25, Sasha Levin wrote:
>   1 file changed, 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
> index 385e9fbbfbe7c..c2817d0c05b69 100644
> --- a/kernel/trace/trace_events_synth.c
> +++ b/kernel/trace/trace_events_synth.c
> @@ -383,13 +383,11 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter,
>   				str_field = (char *)entry + data_offset;
>   
>   				trace_seq_printf(s, print_fmt, se->fields[i]->name,
> -						 STR_VAR_LEN_MAX,
>   						 str_field,
>   						 i == se->n_fields - 1 ? "" : " ");
>   				n_u64++;
>   			} else {
>   				trace_seq_printf(s, print_fmt, se->fields[i]->name,
> -						 STR_VAR_LEN_MAX,
>   						 (char *)&entry->fields[n_u64],
>   						 i == se->n_fields - 1 ? "" : " ");
>   				n_u64 += STR_VAR_LEN_MAX / sizeof(u64);

This looks consistent to me with that patch:
[PATCH v2] tracing: Fix synth event printk format for str fields

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index e3f7d09e5512..f71e49cd35b0 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -305,7 +305,7 @@ static const char *synth_field_fmt(char *type)
         else if (strcmp(type, "gfp_t") == 0)
                 fmt = "%x";
         else if (synth_field_is_string(type))
-               fmt = "%.*s";
+               fmt = "%s";
         else if (synth_field_is_stack(type))
                 fmt = "%s";
  
I only tested the trace.dat route when writing it, thanks for catching this case.


Cheers,

Douglas