[PATCH v3 0/4] tracing: improve symbolic printing

[PATCH v3 0/4] tracing: improve symbolic printing

[Johannes Berg]

Completely forgot about this again ... here's another respin.

v2 was:
 - rebased on 6.9-rc1
 - always search for __print_sym() and get rid of the DYNPRINT flag
   and associated code; I think ideally we'll just remove the older
   __print_symbolic() entirely
 - use ':' as the separator instead of "//" since that makes searching
   for it much easier and it's still not a valid char in an identifier
 - fix RCU

v3:
 - fix #undef issues
 - fix drop_monitor default
 - rebase on linux-trace/for-next (there were no conflicts)
 - move net patches to 3/4
 - clarify symbol name matching logic (and remove ")" from it)

To recap, it's annoying to have

 irq/65-iwlwifi:-401   [000]    22.790000: kfree_skb:  ...  reason: 0x20000

and much nicer to see

 irq/65-iwlwifi:-401   [000]    22.790000: kfree_skb:  ...  reason: RX_DROP_MONITOR

but this doesn't work now because __print_symbolic() can only
deal with a hard-coded list (which is actually really big.)

So here's __print_sym() which doesn't build the list into the
kernel image, but creates it at runtime. For userspace, it
will look the same as __print_symbolic() (it literally shows
__print_symbolic() to userspace) so no changes are needed,
but the actual list of values exposed to userspace in there
is built dynamically. For SKB drop reasons, this then has all
the reasons known when userspace queries the trace format.

I guess patch 3/4 should go through net-next, so not sure
how to handle this patch series. Or perhaps, as this will not
cause conflicts, in fact I've been rebasing it for a long time,
go through tracing anyway with an Ack from netdev? But I can
also just wait for the trace patch(es) to land and resubmit the
net patches after. Assuming this looks good at all :-)

Thanks,
johannes

%

[PATCH v3 1/4] tracing: add __print_sym() to replace __print_symbolic()

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

The way __print_symbolic() works is limited and inefficient
in multiple ways:
 - you can only use it with a static list of symbols, but
   e.g. the SKB dropreasons are now a dynamic list

 - it builds the list in memory _three_ times, so it takes
   a lot of memory:
   - The print_fmt contains the list (since it's passed to
     the macro there). This actually contains the names
     _twice_, which is fixed up at runtime.
   - TRACE_DEFINE_ENUM() puts a 24-byte struct trace_eval_map
     for every entry, plus the string pointed to by it, which
     cannot be deduplicated with the strings in the print_fmt
   - The in-kernel symbolic printing creates yet another list
     of struct trace_print_flags for trace_print_symbols_seq()

 - it also requires runtime fixup during init, which is a lot
   of string parsing due to the print_fmt fixup

Introduce __print_sym() to - over time - replace the old one.
We can easily extend this also to __print_flags later, but I
cared only about the SKB dropreasons for now, which has only
__print_symbolic().

This new __print_sym() requires only a single list of items,
created by TRACE_DEFINE_SYM_LIST(), or can even use another
already existing list by using TRACE_DEFINE_SYM_FNS() with
lookup and show methods.

Then, instead of doing an init-time fixup, just do this at the
time when userspace reads the print_fmt. This way, dynamically
updated lists are possible.

For userspace, nothing actually changes, because the print_fmt
is shown exactly the same way the old __print_symbolic() was.

This adds about 4k .text in my test builds, but that'll be
more than paid for by the actual conversions.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
v2:
 - fix RCU
 - use ':' as separator to simplify the code, that's
   still not valid in a C identifier
v3:
 - add missing #undef lines (reported by Simon Horman)
 - clarify name is not NUL-terminated and fix logic
   for the comparison for that
---
 include/asm-generic/vmlinux.lds.h          |  3 +-
 include/linux/module.h                     |  2 +
 include/linux/trace_events.h               |  7 ++
 include/linux/tracepoint.h                 | 20 +++++
 include/trace/stages/init.h                | 55 +++++++++++++
 include/trace/stages/stage2_data_offsets.h |  6 ++
 include/trace/stages/stage3_trace_output.h |  9 ++
 include/trace/stages/stage7_class_define.h |  3 +
 kernel/module/main.c                       |  3 +
 kernel/trace/trace_events.c                | 95 +++++++++++++++++++++-
 kernel/trace/trace_output.c                | 45 ++++++++++
 11 files changed, 245 insertions(+), 3 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 5703526d6ebf..8275a06bcaee 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -258,7 +258,8 @@
 #define FTRACE_EVENTS()							\
 	. = ALIGN(8);							\
 	BOUNDED_SECTION(_ftrace_events)					\
-	BOUNDED_SECTION_BY(_ftrace_eval_map, _ftrace_eval_maps)
+	BOUNDED_SECTION_BY(_ftrace_eval_map, _ftrace_eval_maps)		\
+	BOUNDED_SECTION(_ftrace_sym_defs)
 #else
 #define FTRACE_EVENTS()
 #endif
diff --git a/include/linux/module.h b/include/linux/module.h
index ffa1c603163c..7256762d59e1 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -524,6 +524,8 @@ struct module {
 	unsigned int num_trace_events;
 	struct trace_eval_map **trace_evals;
 	unsigned int num_trace_evals;
+	struct trace_sym_def **trace_sym_defs;
+	unsigned int num_trace_sym_defs;
 #endif
 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
 	unsigned int num_ftrace_callsites;
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 9df3e2973626..2743280c9a46 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -27,6 +27,13 @@ const char *trace_print_flags_seq(struct trace_seq *p, const char *delim,
 const char *trace_print_symbols_seq(struct trace_seq *p, unsigned long val,
 				    const struct trace_print_flags *symbol_array);
 
+const char *trace_print_sym_seq(struct trace_seq *p, unsigned long long val,
+				const char *(*lookup)(unsigned long long val));
+const char *trace_sym_lookup(const struct trace_sym_entry *list,
+			     size_t len, unsigned long long value);
+void trace_sym_show(struct seq_file *m,
+		    const struct trace_sym_entry *list, size_t len);
+
 #if BITS_PER_LONG == 32
 const char *trace_print_flags_seq_u64(struct trace_seq *p, const char *delim,
 		      unsigned long long flags,
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 689b6d71590e..cc3b387953d1 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -31,6 +31,24 @@ struct trace_eval_map {
 	unsigned long		eval_value;
 };
 
+struct trace_sym_def {
+	const char		*system;
+	const char		*symbol_id;
+	/* may return NULL, called under rcu_read_lock() */
+	const char *		(*lookup)(unsigned long long);
+	/*
+	 * Must print the list: ', { val, "name"}, ...'
+	 * with no trailing comma, but with the leading ', '
+	 * to simplify things:
+	 */
+	void 			(*show)(struct seq_file *);
+};
+
+struct trace_sym_entry {
+	unsigned long long	value;
+	const char		*name;
+};
+
 #define TRACEPOINT_DEFAULT_PRIO	10
 
 extern struct srcu_struct tracepoint_srcu;
@@ -109,6 +127,8 @@ extern void syscall_unregfunc(void);
 
 #define TRACE_DEFINE_ENUM(x)
 #define TRACE_DEFINE_SIZEOF(x)
+#define TRACE_DEFINE_SYM_FNS(...)
+#define TRACE_DEFINE_SYM_LIST(...)
 
 #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
 static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
diff --git a/include/trace/stages/init.h b/include/trace/stages/init.h
index 000bcfc8dd2e..ef63ab64250d 100644
--- a/include/trace/stages/init.h
+++ b/include/trace/stages/init.h
@@ -23,6 +23,61 @@ TRACE_MAKE_SYSTEM_STR();
 	__section("_ftrace_eval_map")			\
 	*TRACE_SYSTEM##_##a = &__##TRACE_SYSTEM##_##a
 
+/*
+ * Define a symbol for __print_sym by giving lookup and
+ * show functions. See &struct trace_sym_def.
+ */
+#undef TRACE_DEFINE_SYM_FNS
+#define TRACE_DEFINE_SYM_FNS(_symbol_id, _lookup, _show)		\
+	_TRACE_DEFINE_SYM_FNS(TRACE_SYSTEM, _symbol_id, _lookup, _show)
+#define _TRACE_DEFINE_SYM_FNS(_system, _symbol_id, _lookup, _show)	\
+	__TRACE_DEFINE_SYM_FNS(_system, _symbol_id, _lookup, _show)
+#define __TRACE_DEFINE_SYM_FNS(_system, _symbol_id, _lookup, _show)	\
+	___TRACE_DEFINE_SYM_FNS(_system ## _ ## _symbol_id, _symbol_id,	\
+				_lookup, _show)
+#define ___TRACE_DEFINE_SYM_FNS(_name, _symbol_id, _lookup, _show)	\
+	static struct trace_sym_def					\
+	__trace_sym_def_ ## _name = {					\
+		.system = TRACE_SYSTEM_STRING,				\
+		.symbol_id = #_symbol_id,				\
+		.lookup = _lookup,					\
+		.show = _show,						\
+	};								\
+	static struct trace_sym_def 					\
+	__section("_ftrace_sym_defs")					\
+	*__trace_sym_def_p_ ## _name = &__trace_sym_def_ ## _name
+
+/*
+ * Define a symbol for __print_sym by giving lookup and
+ * show functions. See &struct trace_sym_def.
+ */
+#undef TRACE_DEFINE_SYM_LIST
+#define TRACE_DEFINE_SYM_LIST(_symbol_id, ...)				\
+	_TRACE_DEFINE_SYM_LIST(TRACE_SYSTEM, _symbol_id, __VA_ARGS__)
+#define _TRACE_DEFINE_SYM_LIST(_system, _symbol_id, ...)		\
+	__TRACE_DEFINE_SYM_LIST(_system, _symbol_id, __VA_ARGS__)
+#define __TRACE_DEFINE_SYM_LIST(_system, _symbol_id, ...)		\
+	___TRACE_DEFINE_SYM_LIST(_system ## _ ## _symbol_id, _symbol_id,\
+				 __VA_ARGS__)
+#define ___TRACE_DEFINE_SYM_LIST(_name, _symbol_id, ...)		\
+	static struct trace_sym_entry					\
+	__trace_sym_list_ ## _name[] = { __VA_ARGS__ };			\
+	static const char *						\
+	__trace_sym_lookup_ ## _name(unsigned long long value)		\
+	{								\
+		return trace_sym_lookup(__trace_sym_list_ ## _name,	\
+			ARRAY_SIZE(__trace_sym_list_ ## _name), value);	\
+	}								\
+	static void							\
+	__trace_sym_show_ ## _name(struct seq_file *m)			\
+	{								\
+		trace_sym_show(m, __trace_sym_list_ ## _name,		\
+			       ARRAY_SIZE(__trace_sym_list_ ## _name));	\
+	}								\
+	___TRACE_DEFINE_SYM_FNS(_name, _symbol_id,			\
+				__trace_sym_lookup_ ## _name,		\
+				__trace_sym_show_ ## _name)
+
 #undef TRACE_DEFINE_SIZEOF
 #define TRACE_DEFINE_SIZEOF(a)				\
 	static struct trace_eval_map __used __initdata	\
diff --git a/include/trace/stages/stage2_data_offsets.h b/include/trace/stages/stage2_data_offsets.h
index 8b0cff06d346..5afd9de7deb3 100644
--- a/include/trace/stages/stage2_data_offsets.h
+++ b/include/trace/stages/stage2_data_offsets.h
@@ -5,6 +5,12 @@
 #undef TRACE_DEFINE_ENUM
 #define TRACE_DEFINE_ENUM(a)
 
+#undef TRACE_DEFINE_SYM_FNS
+#define TRACE_DEFINE_SYM_FNS(_symbol_id, _lookup, _show)
+
+#undef TRACE_DEFINE_SYM_LIST
+#define TRACE_DEFINE_SYM_LIST(_symbol_id, ...)
+
 #undef TRACE_DEFINE_SIZEOF
 #define TRACE_DEFINE_SIZEOF(a)
 
diff --git a/include/trace/stages/stage3_trace_output.h b/include/trace/stages/stage3_trace_output.h
index c1fb1355d309..d2c6458b62dc 100644
--- a/include/trace/stages/stage3_trace_output.h
+++ b/include/trace/stages/stage3_trace_output.h
@@ -79,6 +79,15 @@
 		trace_print_symbols_seq(p, value, symbols);		\
 	})
 
+#undef __print_sym
+#define __print_sym(value, symbol_id)					\
+	___print_sym(TRACE_SYSTEM, value, symbol_id)
+#define ___print_sym(sys, value, symbol_id)				\
+	____print_sym(sys, value, symbol_id)
+#define ____print_sym(sys, value, symbol_id)				\
+	trace_print_sym_seq(p, value,					\
+		__trace_sym_def_p_ ## sys ## _ ## symbol_id->lookup)
+
 #undef __print_flags_u64
 #undef __print_symbolic_u64
 #if BITS_PER_LONG == 32
diff --git a/include/trace/stages/stage7_class_define.h b/include/trace/stages/stage7_class_define.h
index bcb960d16fc0..cf552916935f 100644
--- a/include/trace/stages/stage7_class_define.h
+++ b/include/trace/stages/stage7_class_define.h
@@ -25,6 +25,9 @@
 #undef __print_hex_dump
 #undef __get_buf
 
+#undef __print_sym
+#define __print_sym(value, symbol_id)	__print_sym(value:symbol_id)
+
 /*
  * The below is not executed in the kernel. It is only what is
  * displayed in the print format for userspace to parse.
diff --git a/kernel/module/main.c b/kernel/module/main.c
index d18a94b973e1..5b1700b56a06 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2179,6 +2179,9 @@ static int find_module_sections(struct module *mod, struct load_info *info)
 	mod->trace_evals = section_objs(info, "_ftrace_eval_map",
 					sizeof(*mod->trace_evals),
 					&mod->num_trace_evals);
+	mod->trace_sym_defs = section_objs(info, "_ftrace_sym_defs",
+					   sizeof(*mod->trace_sym_defs),
+					   &mod->num_trace_sym_defs);
 #endif
 #ifdef CONFIG_TRACING
 	mod->trace_bprintk_fmt_start = section_objs(info, "__trace_printk_fmt",
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 6ef29eba90ce..609011e3d472 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1570,6 +1570,98 @@ static void *f_next(struct seq_file *m, void *v, loff_t *pos)
 		return node;
 }
 
+extern struct trace_sym_def *__start_ftrace_sym_defs[];
+extern struct trace_sym_def *__stop_ftrace_sym_defs[];
+
+/* note: @name is not NUL-terminated */
+static void show_sym_list(struct seq_file *m, struct trace_event_call *call,
+			  const char *name, unsigned int name_len)
+{
+	struct trace_sym_def **sym_defs;
+	unsigned int n_sym_defs, i;
+
+	if (call->module) {
+		struct module *mod = call->module;
+
+		sym_defs = mod->trace_sym_defs;
+		n_sym_defs = mod->num_trace_sym_defs;
+	} else {
+		sym_defs = __start_ftrace_sym_defs;
+		n_sym_defs = __stop_ftrace_sym_defs - __start_ftrace_sym_defs;
+	}
+
+	for (i = 0; i < n_sym_defs; i++) {
+		unsigned int sym_len;
+
+		if (!sym_defs[i])
+			continue;
+		if (sym_defs[i]->system != call->class->system)
+			continue;
+		sym_len = strlen(sym_defs[i]->symbol_id);
+		if (name_len != sym_len)
+			continue;
+		if (strncmp(sym_defs[i]->symbol_id, name, sym_len))
+			continue;
+		if (sym_defs[i]->show)
+			sym_defs[i]->show(m);
+		break;
+	}
+}
+
+static void show_print_fmt(struct seq_file *m, struct trace_event_call *call)
+{
+	char *ptr = call->print_fmt;
+	bool in_print_sym = false;
+	int quote = 0;
+
+	seq_puts(m, "\nprint fmt: ");
+	while (*ptr) {
+		if (*ptr == '\\') {
+			seq_putc(m, *ptr);
+			ptr++;
+			/* paranoid */
+			if (!*ptr)
+				break;
+			goto next;
+		}
+		if (*ptr == '"') {
+			quote ^= 1;
+			goto next;
+		}
+		if (quote)
+			goto next;
+
+		if (in_print_sym && *ptr != ':')
+			goto next;
+
+		if (in_print_sym && *ptr == ':') {
+			const char *name;
+
+			ptr++;
+			name = ptr;
+			/* skip the name */
+			while (*ptr && *ptr != ')')
+				ptr++;
+			/* and show the actual list inline now */
+			show_sym_list(m, call, name, ptr - name);
+			in_print_sym = false;
+			continue;
+		}
+
+		if (strncmp(ptr, "__print_sym(", 12) == 0) {
+			ptr += 12;
+			seq_puts(m, "__print_symbolic(");
+			in_print_sym = true;
+			continue;
+		}
+next:
+		seq_putc(m, *ptr);
+		ptr++;
+	}
+
+	seq_putc(m, '\n');
+}
+
 static int f_show(struct seq_file *m, void *v)
 {
 	struct trace_event_call *call = event_file_data(m->private);
@@ -1588,8 +1680,7 @@ static int f_show(struct seq_file *m, void *v)
 		return 0;
 
 	case FORMAT_PRINTFMT:
-		seq_printf(m, "\nprint fmt: %s\n",
-			   call->print_fmt);
+		show_print_fmt(m, call);
 		return 0;
 	}
 
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index d8b302d01083..8a3aa661ea46 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -124,6 +124,51 @@ trace_print_symbols_seq(struct trace_seq *p, unsigned long val,
 }
 EXPORT_SYMBOL(trace_print_symbols_seq);
 
+const char *trace_sym_lookup(const struct trace_sym_entry *list,
+			     size_t len, unsigned long long value)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++) {
+		if (list[i].value == value)
+			return list[i].name;
+	}
+	return NULL;
+}
+EXPORT_SYMBOL(trace_sym_lookup);
+
+void trace_sym_show(struct seq_file *m,
+		    const struct trace_sym_entry *list, size_t len)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++)
+		seq_printf(m, ", { %lld, \"%s\" }",
+			   list[i].value, list[i].name);
+}
+EXPORT_SYMBOL(trace_sym_show);
+
+const char *
+trace_print_sym_seq(struct trace_seq *p, unsigned long long val,
+		    const char *(*lookup)(unsigned long long val))
+{
+	const char *ret = trace_seq_buffer_ptr(p);
+	const char *name;
+
+	rcu_read_lock();
+	name = lookup(val);
+	if (name)
+		trace_seq_puts(p, name);
+	else
+		trace_seq_printf(p, "0x%llx", val);
+	rcu_read_unlock();
+
+	trace_seq_putc(p, 0);
+
+	return ret;
+}
+EXPORT_SYMBOL(trace_print_sym_seq);
+
 #if BITS_PER_LONG == 32
 const char *
 trace_print_flags_seq_u64(struct trace_seq *p, const char *delim,
-- 
2.45.1

[PATCH v3 2/4] tracing/timer: use __print_sym()

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

Use the new __print_sym() in the timer tracing, just to show
how to convert something. This adds ~80 bytes of .text for a
saving of ~1.5K of data in my builds.

Note the format changes from

print fmt: "success=%d dependency=%s", REC->success, __print_symbolic(REC->dependency, { 0, "NONE" }, { (1 << 0), "POSIX_TIMER" }, { (1 << 1), "PERF_EVENTS" }, { (1 << 2), "SCHED" }, { (1 << 3), "CLOCK_UNSTABLE" }, { (1 << 4), "RCU" }, { (1 << 5), "RCU_EXP" })

to

print fmt: "success=%d dependency=%s", REC->success, __print_symbolic(REC->dependency, { 0, "NONE" }, { 1, "POSIX_TIMER" }, { 2, "PERF_EVENTS" }, { 4, "SCHED" }, { 8, "CLOCK_UNSTABLE" }, { 16, "RCU" }, { 32, "RCU_EXP" })

since the values are now just printed in the show function as
pure decimal values.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 include/trace/events/timer.h | 22 +++++++---------------
 1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
index 1ef58a04fc57..d483abffed78 100644
--- a/include/trace/events/timer.h
+++ b/include/trace/events/timer.h
@@ -402,26 +402,18 @@ TRACE_EVENT(itimer_expire,
 #undef tick_dep_mask_name
 #undef tick_dep_name_end
 
-/* The MASK will convert to their bits and they need to be processed too */
-#define tick_dep_name(sdep) TRACE_DEFINE_ENUM(TICK_DEP_BIT_##sdep); \
-	TRACE_DEFINE_ENUM(TICK_DEP_MASK_##sdep);
-#define tick_dep_name_end(sdep)  TRACE_DEFINE_ENUM(TICK_DEP_BIT_##sdep); \
-	TRACE_DEFINE_ENUM(TICK_DEP_MASK_##sdep);
-/* NONE only has a mask defined for it */
-#define tick_dep_mask_name(sdep) TRACE_DEFINE_ENUM(TICK_DEP_MASK_##sdep);
-
-TICK_DEP_NAMES
-
-#undef tick_dep_name
-#undef tick_dep_mask_name
-#undef tick_dep_name_end
-
 #define tick_dep_name(sdep) { TICK_DEP_MASK_##sdep, #sdep },
 #define tick_dep_mask_name(sdep) { TICK_DEP_MASK_##sdep, #sdep },
 #define tick_dep_name_end(sdep) { TICK_DEP_MASK_##sdep, #sdep }
 
+TRACE_DEFINE_SYM_LIST(tick_dep_names, TICK_DEP_NAMES);
+
+#undef tick_dep_name
+#undef tick_dep_mask_name
+#undef tick_dep_name_end
+
 #define show_tick_dep_name(val)				\
-	__print_symbolic(val, TICK_DEP_NAMES)
+	__print_sym(val, tick_dep_names)
 
 TRACE_EVENT(tick_stop,
 
-- 
2.45.1

[PATCH v3 3/4] net: dropreason: use new __print_sym() in tracing

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

The __print_symbolic() could only ever print the core
drop reasons, since that's the way the infrastructure
works. Now that we have __print_sym() with all the
advantages mentioned in that commit, convert to that
and get all the drop reasons from all subsystems. As
we already have a list of them, that's really easy.

This is a little bit of .text (~100 bytes in my build)
and saves a lot of .data (~17k).

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 include/net/dropreason.h   |  5 +++++
 include/trace/events/skb.h | 16 +++-----------
 net/core/skbuff.c          | 43 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+), 13 deletions(-)

diff --git a/include/net/dropreason.h b/include/net/dropreason.h
index 56cb7be92244..c157070b5303 100644
--- a/include/net/dropreason.h
+++ b/include/net/dropreason.h
@@ -42,6 +42,11 @@ struct drop_reason_list {
 extern const struct drop_reason_list __rcu *
 drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM];
 
+#ifdef CONFIG_TRACEPOINTS
+const char *drop_reason_lookup(unsigned long long value);
+void drop_reason_show(struct seq_file *m);
+#endif
+
 void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
 				  const struct drop_reason_list *list);
 void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys);
diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
index 07e0715628ec..8a1a63f9e796 100644
--- a/include/trace/events/skb.h
+++ b/include/trace/events/skb.h
@@ -8,15 +8,9 @@
 #include <linux/skbuff.h>
 #include <linux/netdevice.h>
 #include <linux/tracepoint.h>
+#include <net/dropreason.h>
 
-#undef FN
-#define FN(reason)	TRACE_DEFINE_ENUM(SKB_DROP_REASON_##reason);
-DEFINE_DROP_REASON(FN, FN)
-
-#undef FN
-#undef FNe
-#define FN(reason)	{ SKB_DROP_REASON_##reason, #reason },
-#define FNe(reason)	{ SKB_DROP_REASON_##reason, #reason }
+TRACE_DEFINE_SYM_FNS(drop_reason, drop_reason_lookup, drop_reason_show);
 
 /*
  * Tracepoint for free an sk_buff:
@@ -44,13 +38,9 @@ TRACE_EVENT(kfree_skb,
 
 	TP_printk("skbaddr=%p protocol=%u location=%pS reason: %s",
 		  __entry->skbaddr, __entry->protocol, __entry->location,
-		  __print_symbolic(__entry->reason,
-				   DEFINE_DROP_REASON(FN, FNe)))
+		  __print_sym(__entry->reason, drop_reason ))
 );
 
-#undef FN
-#undef FNe
-
 TRACE_EVENT(consume_skb,
 
 	TP_PROTO(struct sk_buff *skb, void *location),
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 466999a7515e..cd1ea6c3e0f8 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -145,6 +145,49 @@ drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM] = {
 };
 EXPORT_SYMBOL(drop_reasons_by_subsys);
 
+#ifdef CONFIG_TRACEPOINTS
+const char *drop_reason_lookup(unsigned long long value)
+{
+	unsigned long long subsys_id = value >> SKB_DROP_REASON_SUBSYS_SHIFT;
+	u32 reason = value & ~SKB_DROP_REASON_SUBSYS_MASK;
+	const struct drop_reason_list *subsys;
+
+	if (subsys_id >= SKB_DROP_REASON_SUBSYS_NUM)
+		return NULL;
+
+	subsys = rcu_dereference(drop_reasons_by_subsys[subsys_id]);
+	if (!subsys)
+		return NULL;
+	if (reason >= subsys->n_reasons)
+		return NULL;
+	return subsys->reasons[reason];
+}
+
+void drop_reason_show(struct seq_file *m)
+{
+	u32 subsys_id;
+
+	rcu_read_lock();
+	for (subsys_id = 0; subsys_id < SKB_DROP_REASON_SUBSYS_NUM; subsys_id++) {
+		const struct drop_reason_list *subsys;
+		u32 i;
+
+		subsys = rcu_dereference(drop_reasons_by_subsys[subsys_id]);
+		if (!subsys)
+			continue;
+
+		for (i = 0; i < subsys->n_reasons; i++) {
+			if (!subsys->reasons[i])
+				continue;
+			seq_printf(m, ", { %u, \"%s\" }",
+				   (subsys_id << SKB_DROP_REASON_SUBSYS_SHIFT) | i,
+				   subsys->reasons[i]);
+		}
+	}
+	rcu_read_unlock();
+}
+#endif
+
 /**
  * drop_reasons_register_subsys - register another drop reason subsystem
  * @subsys: the subsystem to register, must not be the core
-- 
2.45.1

[PATCH v3 4/4] net: drop_monitor: use drop_reason_lookup()

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

Now that we have drop_reason_lookup(), we can just use it for
drop_monitor as well, rather than exporting the list itself.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
v3:
 - look up SKB_DROP_REASON_NOT_SPECIFIED if initial lookup
   returns NULL, to preserve previous behaviour
---
 include/net/dropreason.h |  4 ----
 net/core/drop_monitor.c  | 20 +++++---------------
 net/core/skbuff.c        |  6 +++---
 3 files changed, 8 insertions(+), 22 deletions(-)

diff --git a/include/net/dropreason.h b/include/net/dropreason.h
index c157070b5303..0e2195ccf2cd 100644
--- a/include/net/dropreason.h
+++ b/include/net/dropreason.h
@@ -38,10 +38,6 @@ struct drop_reason_list {
 	size_t n_reasons;
 };
 
-/* Note: due to dynamic registrations, access must be under RCU */
-extern const struct drop_reason_list __rcu *
-drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM];
-
 #ifdef CONFIG_TRACEPOINTS
 const char *drop_reason_lookup(unsigned long long value);
 void drop_reason_show(struct seq_file *m);
diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 430ed18f8584..fddf6b68bf06 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -610,9 +610,8 @@ static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
 				     size_t payload_len)
 {
 	struct net_dm_skb_cb *cb = NET_DM_SKB_CB(skb);
-	const struct drop_reason_list *list = NULL;
-	unsigned int subsys, subsys_reason;
 	char buf[NET_DM_MAX_SYMBOL_LEN];
+	const char *reason_str;
 	struct nlattr *attr;
 	void *hdr;
 	int rc;
@@ -630,19 +629,10 @@ static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
 		goto nla_put_failure;
 
 	rcu_read_lock();
-	subsys = u32_get_bits(cb->reason, SKB_DROP_REASON_SUBSYS_MASK);
-	if (subsys < SKB_DROP_REASON_SUBSYS_NUM)
-		list = rcu_dereference(drop_reasons_by_subsys[subsys]);
-	subsys_reason = cb->reason & ~SKB_DROP_REASON_SUBSYS_MASK;
-	if (!list ||
-	    subsys_reason >= list->n_reasons ||
-	    !list->reasons[subsys_reason] ||
-	    strlen(list->reasons[subsys_reason]) > NET_DM_MAX_REASON_LEN) {
-		list = rcu_dereference(drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_CORE]);
-		subsys_reason = SKB_DROP_REASON_NOT_SPECIFIED;
-	}
-	if (nla_put_string(msg, NET_DM_ATTR_REASON,
-			   list->reasons[subsys_reason])) {
+	reason_str = drop_reason_lookup(cb->reason);
+	if (unlikely(!reason_str))
+		reason_str = drop_reason_lookup(SKB_DROP_REASON_NOT_SPECIFIED);
+	if (nla_put_string(msg, NET_DM_ATTR_REASON, reason_str)) {
 		rcu_read_unlock();
 		goto nla_put_failure;
 	}
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index cd1ea6c3e0f8..bd4fb7410284 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -139,13 +139,11 @@ static const struct drop_reason_list drop_reasons_core = {
 	.n_reasons = ARRAY_SIZE(drop_reasons),
 };
 
-const struct drop_reason_list __rcu *
+static const struct drop_reason_list __rcu *
 drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM] = {
 	[SKB_DROP_REASON_SUBSYS_CORE] = RCU_INITIALIZER(&drop_reasons_core),
 };
-EXPORT_SYMBOL(drop_reasons_by_subsys);
 
-#ifdef CONFIG_TRACEPOINTS
 const char *drop_reason_lookup(unsigned long long value)
 {
 	unsigned long long subsys_id = value >> SKB_DROP_REASON_SUBSYS_SHIFT;
@@ -162,7 +160,9 @@ const char *drop_reason_lookup(unsigned long long value)
 		return NULL;
 	return subsys->reasons[reason];
 }
+EXPORT_SYMBOL(drop_reason_lookup);
 
+#ifdef CONFIG_TRACEPOINTS
 void drop_reason_show(struct seq_file *m)
 {
 	u32 subsys_id;
-- 
2.45.1

Re: [PATCH v3 1/4] tracing: add __print_sym() to replace __print_symbolic()

[kernel test robot]

Hi Johannes,

kernel test robot noticed the following build errors:

[auto build test ERROR on mcgrof/modules-next]
[also build test ERROR on arnd-asm-generic/master tip/timers/core net/main net-next/main linus/master horms-ipvs/master v6.10-rc2 next-20240607]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Johannes-Berg/tracing-add-__print_sym-to-replace-__print_symbolic/20240607-043503
base:   https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git modules-next
patch link:    https://lore.kernel.org/r/20240606203255.49433-7-johannes%40sipsolutions.net
patch subject: [PATCH v3 1/4] tracing: add __print_sym() to replace __print_symbolic()
config: arc-randconfig-002-20240607 (https://download.01.org/0day-ci/archive/20240607/202406072129.3ZzFDOlC-lkp@intel.com/config)
compiler: arc-elf-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240607/202406072129.3ZzFDOlC-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202406072129.3ZzFDOlC-lkp@intel.com/

All errors (new ones prefixed by >>):

   kernel/trace/trace_events.c: In function 'show_sym_list':
>> kernel/trace/trace_events.c:1586:31: error: invalid use of undefined type 'struct module'
    1586 |                 sym_defs = mod->trace_sym_defs;
         |                               ^~
   kernel/trace/trace_events.c:1587:33: error: invalid use of undefined type 'struct module'
    1587 |                 n_sym_defs = mod->num_trace_sym_defs;
         |                                 ^~


vim +1586 kernel/trace/trace_events.c

  1575	
  1576	/* note: @name is not NUL-terminated */
  1577	static void show_sym_list(struct seq_file *m, struct trace_event_call *call,
  1578				  const char *name, unsigned int name_len)
  1579	{
  1580		struct trace_sym_def **sym_defs;
  1581		unsigned int n_sym_defs, i;
  1582	
  1583		if (call->module) {
  1584			struct module *mod = call->module;
  1585	
> 1586			sym_defs = mod->trace_sym_defs;
  1587			n_sym_defs = mod->num_trace_sym_defs;
  1588		} else {
  1589			sym_defs = __start_ftrace_sym_defs;
  1590			n_sym_defs = __stop_ftrace_sym_defs - __start_ftrace_sym_defs;
  1591		}
  1592	
  1593		for (i = 0; i < n_sym_defs; i++) {
  1594			unsigned int sym_len;
  1595	
  1596			if (!sym_defs[i])
  1597				continue;
  1598			if (sym_defs[i]->system != call->class->system)
  1599				continue;
  1600			sym_len = strlen(sym_defs[i]->symbol_id);
  1601			if (name_len != sym_len)
  1602				continue;
  1603			if (strncmp(sym_defs[i]->symbol_id, name, sym_len))
  1604				continue;
  1605			if (sym_defs[i]->show)
  1606				sym_defs[i]->show(m);
  1607			break;
  1608		}
  1609	}
  1610	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v3 1/4] tracing: add __print_sym() to replace __print_symbolic()

[kernel test robot]

Hi Johannes,

kernel test robot noticed the following build errors:

[auto build test ERROR on mcgrof/modules-next]
[also build test ERROR on arnd-asm-generic/master tip/timers/core net/main net-next/main linus/master horms-ipvs/master v6.10-rc2 next-20240607]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Johannes-Berg/tracing-add-__print_sym-to-replace-__print_symbolic/20240607-043503
base:   https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git modules-next
patch link:    https://lore.kernel.org/r/20240606203255.49433-7-johannes%40sipsolutions.net
patch subject: [PATCH v3 1/4] tracing: add __print_sym() to replace __print_symbolic()
config: arm64-randconfig-002-20240607 (https://download.01.org/0day-ci/archive/20240607/202406072141.OLmqbch3-lkp@intel.com/config)
compiler: clang version 19.0.0git (https://github.com/llvm/llvm-project d7d2d4f53fc79b4b58e8d8d08151b577c3699d4a)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240607/202406072141.OLmqbch3-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202406072141.OLmqbch3-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from kernel/trace/trace_events.c:15:
   In file included from include/linux/security.h:33:
   In file included from include/linux/mm.h:2210:
   include/linux/vmstat.h:522:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
     522 |         return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
         |                               ~~~~~~~~~~~ ^ ~~~
>> kernel/trace/trace_events.c:1586:17: error: incomplete definition of type 'struct module'
    1586 |                 sym_defs = mod->trace_sym_defs;
         |                            ~~~^
   include/linux/printk.h:350:8: note: forward declaration of 'struct module'
     350 | struct module;
         |        ^
   kernel/trace/trace_events.c:1587:19: error: incomplete definition of type 'struct module'
    1587 |                 n_sym_defs = mod->num_trace_sym_defs;
         |                              ~~~^
   include/linux/printk.h:350:8: note: forward declaration of 'struct module'
     350 | struct module;
         |        ^
   1 warning and 2 errors generated.


vim +1586 kernel/trace/trace_events.c

  1575	
  1576	/* note: @name is not NUL-terminated */
  1577	static void show_sym_list(struct seq_file *m, struct trace_event_call *call,
  1578				  const char *name, unsigned int name_len)
  1579	{
  1580		struct trace_sym_def **sym_defs;
  1581		unsigned int n_sym_defs, i;
  1582	
  1583		if (call->module) {
  1584			struct module *mod = call->module;
  1585	
> 1586			sym_defs = mod->trace_sym_defs;
  1587			n_sym_defs = mod->num_trace_sym_defs;
  1588		} else {
  1589			sym_defs = __start_ftrace_sym_defs;
  1590			n_sym_defs = __stop_ftrace_sym_defs - __start_ftrace_sym_defs;
  1591		}
  1592	
  1593		for (i = 0; i < n_sym_defs; i++) {
  1594			unsigned int sym_len;
  1595	
  1596			if (!sym_defs[i])
  1597				continue;
  1598			if (sym_defs[i]->system != call->class->system)
  1599				continue;
  1600			sym_len = strlen(sym_defs[i]->symbol_id);
  1601			if (name_len != sym_len)
  1602				continue;
  1603			if (strncmp(sym_defs[i]->symbol_id, name, sym_len))
  1604				continue;
  1605			if (sym_defs[i]->show)
  1606				sym_defs[i]->show(m);
  1607			break;
  1608		}
  1609	}
  1610	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki