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Message-Id: <20251112141705.a7f2f79f6d7b058201307e89@kernel.org>
Date: Wed, 12 Nov 2025 14:17:05 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Donglin Peng <dolinux.peng@...il.com>
Cc: rostedt@...dmis.org, linux-trace-kernel@...r.kernel.org,
linux-kernel@...r.kernel.org, Donglin Peng <pengdonglin@...omi.com>, Sven
Schnelle <svens@...ux.ibm.com>, Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v3 RESEND] function_graph: Enable funcgraph-args and
funcgraph-retaddr to work simultaneously
On Wed, 12 Nov 2025 11:43:33 +0800
Donglin Peng <dolinux.peng@...il.com> wrote:
> From: Donglin Peng <pengdonglin@...omi.com>
>
> Currently, the funcgraph-args and funcgraph-retaddr features are mutually exclusive.
> This patch resolves this limitation by modifying funcgraph-retaddr to adopt the same
> implementation approach as funcgraph-args, specifically by storing the return address
> in the first entry of the args array.
>
> As a result, both features now coexist seamlessly and function as intended.
>
> To verify the change, use perf to trace vfs_write with both options enabled:
>
> Before:
> # perf ftrace -G vfs_write --graph-opts args,retaddr
> ......
> 0) | down_read() { /* <-n_tty_write+0xa3/0x540 */
> 0) 0.075 us | __cond_resched(); /* <-down_read+0x12/0x160 */
> 0) 0.079 us | preempt_count_add(); /* <-down_read+0x3b/0x160 */
> 0) 0.077 us | preempt_count_sub(); /* <-down_read+0x8b/0x160 */
> 0) 0.754 us | }
>
> After:
> # perf ftrace -G vfs_write --graph-opts args,retaddr
> ......
> 0) | down_read(sem=0xffff8880100bea78) { /* <-n_tty_write+0xa3/0x540 */
> 0) 0.075 us | __cond_resched(); /* <-down_read+0x12/0x160 */
> 0) 0.079 us | preempt_count_add(val=1); /* <-down_read+0x3b/0x160 */
> 0) 0.077 us | preempt_count_sub(val=1); /* <-down_read+0x8b/0x160 */
> 0) 0.754 us | }
>
> Cc: Steven Rostedt (Google) <rostedt@...dmis.org>
> Cc: Sven Schnelle <svens@...ux.ibm.com>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Signed-off-by: Donglin Peng <pengdonglin@...omi.com>
Looks good to me except for a few nits, but it's a style issue.
Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Thank you,
> ---
> v3:
> - Replace min() with min_t() to improve type safety and maintainability
> - Keep only one Signed-off-by for cleaner attribution
> - Code refactoring for improved readability
>
> v2:
> - Preserve retaddr event functionality (suggested by Steven)
> - Store the retaddr in args[0] (suggested by Steven)
> - Refactor implementation logic and commit message clarity
> ---
> include/linux/ftrace.h | 11 --
> kernel/trace/trace.h | 4 -
> kernel/trace/trace_entries.h | 6 +-
> kernel/trace/trace_functions_graph.c | 145 ++++++++++++---------------
> 4 files changed, 69 insertions(+), 97 deletions(-)
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 7ded7df6e9b5..88cb54d73bdb 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -1129,17 +1129,6 @@ struct ftrace_graph_ent {
> int depth;
> } __packed;
>
> -/*
> - * Structure that defines an entry function trace with retaddr.
> - * It's already packed but the attribute "packed" is needed
> - * to remove extra padding at the end.
> - */
> -struct fgraph_retaddr_ent {
> - unsigned long func; /* Current function */
> - int depth;
> - unsigned long retaddr; /* Return address */
> -} __packed;
> -
> /*
> * Structure that defines a return function trace.
> * It's already packed but the attribute "packed" is needed
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 85eabb454bee..9fac291b913a 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -955,10 +955,6 @@ extern void graph_trace_close(struct trace_iterator *iter);
> extern int __trace_graph_entry(struct trace_array *tr,
> struct ftrace_graph_ent *trace,
> unsigned int trace_ctx);
> -extern int __trace_graph_retaddr_entry(struct trace_array *tr,
> - struct ftrace_graph_ent *trace,
> - unsigned int trace_ctx,
> - unsigned long retaddr);
> extern void __trace_graph_return(struct trace_array *tr,
> struct ftrace_graph_ret *trace,
> unsigned int trace_ctx,
> diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
> index de294ae2c5c5..593a74663c65 100644
> --- a/kernel/trace/trace_entries.h
> +++ b/kernel/trace/trace_entries.h
> @@ -95,14 +95,14 @@ FTRACE_ENTRY_PACKED(fgraph_retaddr_entry, fgraph_retaddr_ent_entry,
> TRACE_GRAPH_RETADDR_ENT,
>
> F_STRUCT(
> - __field_struct( struct fgraph_retaddr_ent, graph_ent )
> + __field_struct( struct ftrace_graph_ent, graph_ent )
> __field_packed( unsigned long, graph_ent, func )
> __field_packed( unsigned int, graph_ent, depth )
> - __field_packed( unsigned long, graph_ent, retaddr )
> + __dynamic_array(unsigned long, args )
> ),
>
> F_printk("--> %ps (%u) <- %ps", (void *)__entry->func, __entry->depth,
> - (void *)__entry->retaddr)
> + (void *)__entry->args[0])
> );
>
> #else
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index a7f4b9a47a71..f31eeeffbb2d 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -16,6 +16,15 @@
> #include "trace.h"
> #include "trace_output.h"
>
> +#ifdef CONFIG_FUNCTION_GRAPH_RETADDR
> +#define HAVE_RETADDR 1
> +#define ARGS_OFFS(args_size) \
> + ((args_size) > FTRACE_REGS_MAX_ARGS * sizeof(long) ? 1 : 0)
> +#else
> +#define HAVE_RETADDR 0
> +#define ARGS_OFFS(args_size) 0
> +#endif
> +
> /* When set, irq functions will be ignored */
> static int ftrace_graph_skip_irqs;
>
> @@ -27,21 +36,25 @@ struct fgraph_cpu_data {
> unsigned long enter_funcs[FTRACE_RETFUNC_DEPTH];
> };
>
> +/*
> + * fgraph_retaddr_ent_entry and ftrace_graph_ent_entry share layout, ent
> + * member repurposed for storage
> + */
> struct fgraph_ent_args {
> struct ftrace_graph_ent_entry ent;
> - /* Force the sizeof of args[] to have FTRACE_REGS_MAX_ARGS entries */
> - unsigned long args[FTRACE_REGS_MAX_ARGS];
> + /*
> + * Force the sizeof of args[] to have (FTRACE_REGS_MAX_ARGS + HAVE_RETADDR)
> + * entries with the first entry storing the return address for
> + * TRACE_GRAPH_RETADDR_ENT.
> + */
> + unsigned long args[FTRACE_REGS_MAX_ARGS + HAVE_RETADDR];
> };
>
> struct fgraph_data {
> struct fgraph_cpu_data __percpu *cpu_data;
>
> /* Place to preserve last processed entry. */
> - union {
> - struct fgraph_ent_args ent;
> - /* TODO allow retaddr to have args */
> - struct fgraph_retaddr_ent_entry rent;
> - };
> + struct fgraph_ent_args ent;
> struct ftrace_graph_ret_entry ret;
> int failed;
> int cpu;
> @@ -127,22 +140,43 @@ static int __graph_entry(struct trace_array *tr, struct ftrace_graph_ent *trace,
> struct ring_buffer_event *event;
> struct trace_buffer *buffer = tr->array_buffer.buffer;
> struct ftrace_graph_ent_entry *entry;
> - int size;
> + unsigned long retaddr = 0;
> + int size = sizeof(*entry);
> + int type = TRACE_GRAPH_ENT;
> + bool store_args = false;
> + int nr_args = 0, args_offs = 0;
> +
> + if (tracer_flags_is_set(TRACE_GRAPH_PRINT_RETADDR)) {
> + retaddr = ftrace_graph_top_ret_addr(current);
> + type = TRACE_GRAPH_RETADDR_ENT;
> + nr_args += 1;
> + }
>
> /* If fregs is defined, add FTRACE_REGS_MAX_ARGS long size words */
> - size = sizeof(*entry) + (FTRACE_REGS_MAX_ARGS * !!fregs * sizeof(long));
> + if (tracer_flags_is_set(TRACE_GRAPH_ARGS)) {
> + store_args = !!fregs;
> + if (store_args)
> + nr_args += FTRACE_REGS_MAX_ARGS;
> + }
>
> - event = trace_buffer_lock_reserve(buffer, TRACE_GRAPH_ENT, size, trace_ctx);
> + size += nr_args * sizeof(long);
> + event = trace_buffer_lock_reserve(buffer, type, size, trace_ctx);
> if (!event)
> return 0;
>
> entry = ring_buffer_event_data(event);
> entry->graph_ent = *trace;
>
> + /* Store the retaddr in args[0] */
> + if (type == TRACE_GRAPH_RETADDR_ENT) {
> + entry->args[0] = retaddr;
> + args_offs += 1;
> + }
> +
> #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
> - if (fregs) {
> + if (store_args) {
> for (int i = 0; i < FTRACE_REGS_MAX_ARGS; i++)
> - entry->args[i] = ftrace_regs_get_argument(fregs, i);
> + entry->args[i + args_offs] = ftrace_regs_get_argument(fregs, i);
> }
> #endif
>
> @@ -158,38 +192,6 @@ int __trace_graph_entry(struct trace_array *tr,
> return __graph_entry(tr, trace, trace_ctx, NULL);
> }
>
> -#ifdef CONFIG_FUNCTION_GRAPH_RETADDR
> -int __trace_graph_retaddr_entry(struct trace_array *tr,
> - struct ftrace_graph_ent *trace,
> - unsigned int trace_ctx,
> - unsigned long retaddr)
> -{
> - struct ring_buffer_event *event;
> - struct trace_buffer *buffer = tr->array_buffer.buffer;
> - struct fgraph_retaddr_ent_entry *entry;
> -
> - event = trace_buffer_lock_reserve(buffer, TRACE_GRAPH_RETADDR_ENT,
> - sizeof(*entry), trace_ctx);
> - if (!event)
> - return 0;
> - entry = ring_buffer_event_data(event);
> - entry->graph_ent.func = trace->func;
> - entry->graph_ent.depth = trace->depth;
> - entry->graph_ent.retaddr = retaddr;
> - trace_buffer_unlock_commit_nostack(buffer, event);
> -
> - return 1;
> -}
> -#else
> -int __trace_graph_retaddr_entry(struct trace_array *tr,
> - struct ftrace_graph_ent *trace,
> - unsigned int trace_ctx,
> - unsigned long retaddr)
> -{
> - return 1;
> -}
> -#endif
> -
> static inline int ftrace_graph_ignore_irqs(void)
> {
> if (!ftrace_graph_skip_irqs || trace_recursion_test(TRACE_IRQ_BIT))
> @@ -211,7 +213,6 @@ static int graph_entry(struct ftrace_graph_ent *trace,
> struct trace_array *tr = gops->private;
> struct fgraph_times *ftimes;
> unsigned int trace_ctx;
> - int ret = 0;
>
> if (*task_var & TRACE_GRAPH_NOTRACE)
> return 0;
> @@ -262,15 +263,7 @@ static int graph_entry(struct ftrace_graph_ent *trace,
> return 1;
>
> trace_ctx = tracing_gen_ctx();
> - if (IS_ENABLED(CONFIG_FUNCTION_GRAPH_RETADDR) &&
> - tracer_flags_is_set(TRACE_GRAPH_PRINT_RETADDR)) {
> - unsigned long retaddr = ftrace_graph_top_ret_addr(current);
> - ret = __trace_graph_retaddr_entry(tr, trace, trace_ctx, retaddr);
> - } else {
> - ret = __graph_entry(tr, trace, trace_ctx, fregs);
> - }
> -
> - return ret;
> + return __graph_entry(tr, trace, trace_ctx, fregs);
> }
>
> int trace_graph_entry(struct ftrace_graph_ent *trace,
> @@ -634,13 +627,9 @@ get_return_for_leaf(struct trace_iterator *iter,
> * Save current and next entries for later reference
> * if the output fails.
> */
> - if (unlikely(curr->ent.type == TRACE_GRAPH_RETADDR_ENT)) {
> - data->rent = *(struct fgraph_retaddr_ent_entry *)curr;
> - } else {
> - int size = min((int)sizeof(data->ent), (int)iter->ent_size);
> + int size = min_t(int, sizeof(data->ent), iter->ent_size);
>
> - memcpy(&data->ent, curr, size);
> - }
> + memcpy(&data->ent, curr, size);
> /*
> * If the next event is not a return type, then
> * we only care about what type it is. Otherwise we can
> @@ -811,21 +800,21 @@ print_graph_duration(struct trace_array *tr, unsigned long long duration,
>
> #ifdef CONFIG_FUNCTION_GRAPH_RETADDR
> #define __TRACE_GRAPH_PRINT_RETADDR TRACE_GRAPH_PRINT_RETADDR
> -static void print_graph_retaddr(struct trace_seq *s, struct fgraph_retaddr_ent_entry *entry,
> - u32 trace_flags, bool comment)
> +static void print_graph_retaddr(struct trace_seq *s, unsigned long retaddr, u32 trace_flags,
> + bool comment)
> {
> if (comment)
> trace_seq_puts(s, " /*");
>
> trace_seq_puts(s, " <-");
> - seq_print_ip_sym(s, entry->graph_ent.retaddr, trace_flags | TRACE_ITER_SYM_OFFSET);
> + seq_print_ip_sym(s, retaddr, trace_flags | TRACE_ITER_SYM_OFFSET);
>
> if (comment)
> trace_seq_puts(s, " */");
> }
> #else
> #define __TRACE_GRAPH_PRINT_RETADDR 0
> -#define print_graph_retaddr(_seq, _entry, _tflags, _comment) do { } while (0)
> +#define print_graph_retaddr(_seq, _retaddr, _tflags, _comment) do { } while (0)
> #endif
>
> #if defined(CONFIG_FUNCTION_GRAPH_RETVAL) || defined(CONFIG_FUNCTION_GRAPH_RETADDR)
> @@ -869,10 +858,12 @@ static void print_graph_retval(struct trace_seq *s, struct ftrace_graph_ent_entr
> trace_seq_printf(s, "%ps", func);
>
> if (args_size >= FTRACE_REGS_MAX_ARGS * sizeof(long)) {
> - print_function_args(s, entry->args, (unsigned long)func);
> + print_function_args(s, entry->args + ARGS_OFFS(args_size),
> + (unsigned long)func);
> trace_seq_putc(s, ';');
> - } else
> + } else {
nit: you don't need to add braces for a single line block.
> trace_seq_puts(s, "();");
> + }
>
> if (print_retval || print_retaddr)
> trace_seq_puts(s, " /*");
> @@ -882,8 +873,7 @@ static void print_graph_retval(struct trace_seq *s, struct ftrace_graph_ent_entr
> }
>
> if (print_retaddr)
> - print_graph_retaddr(s, (struct fgraph_retaddr_ent_entry *)entry,
> - trace_flags, false);
> + print_graph_retaddr(s, entry->args[0], trace_flags, false);
>
> if (print_retval) {
> if (hex_format || (err_code == 0))
> @@ -964,10 +954,12 @@ print_graph_entry_leaf(struct trace_iterator *iter,
> trace_seq_printf(s, "%ps", (void *)ret_func);
>
> if (args_size >= FTRACE_REGS_MAX_ARGS * sizeof(long)) {
> - print_function_args(s, entry->args, ret_func);
> + print_function_args(s, entry->args + ARGS_OFFS(args_size),
> + ret_func);
> trace_seq_putc(s, ';');
> - } else
> + } else {
Ditto.
> trace_seq_puts(s, "();");
> + }
> }
> trace_seq_putc(s, '\n');
>
> @@ -1016,7 +1008,7 @@ print_graph_entry_nested(struct trace_iterator *iter,
> args_size = iter->ent_size - offsetof(struct ftrace_graph_ent_entry, args);
>
> if (args_size >= FTRACE_REGS_MAX_ARGS * sizeof(long))
> - print_function_args(s, entry->args, func);
> + print_function_args(s, entry->args + ARGS_OFFS(args_size), func);
> else
> trace_seq_puts(s, "()");
>
> @@ -1024,8 +1016,7 @@ print_graph_entry_nested(struct trace_iterator *iter,
>
> if (flags & __TRACE_GRAPH_PRINT_RETADDR &&
> entry->ent.type == TRACE_GRAPH_RETADDR_ENT)
> - print_graph_retaddr(s, (struct fgraph_retaddr_ent_entry *)entry,
> - tr->trace_flags, true);
> + print_graph_retaddr(s, entry->args[0], tr->trace_flags, true);
> trace_seq_putc(s, '\n');
>
> if (trace_seq_has_overflowed(s))
> @@ -1202,7 +1193,7 @@ print_graph_entry(struct ftrace_graph_ent_entry *field, struct trace_seq *s,
> * it can be safely saved at the stack.
> */
> struct ftrace_graph_ent_entry *entry;
> - u8 save_buf[sizeof(*entry) + FTRACE_REGS_MAX_ARGS * sizeof(long)];
> + u8 save_buf[sizeof(*entry) + (FTRACE_REGS_MAX_ARGS + HAVE_RETADDR) * sizeof(long)];
>
> /* The ent_size is expected to be as big as the entry */
> if (iter->ent_size > sizeof(save_buf))
> @@ -1429,16 +1420,12 @@ print_graph_function_flags(struct trace_iterator *iter, u32 flags)
> trace_assign_type(field, entry);
> return print_graph_entry(field, s, iter, flags);
> }
> -#ifdef CONFIG_FUNCTION_GRAPH_RETADDR
> case TRACE_GRAPH_RETADDR_ENT: {
> - struct fgraph_retaddr_ent_entry saved;
> struct fgraph_retaddr_ent_entry *rfield;
>
> trace_assign_type(rfield, entry);
> - saved = *rfield;
> - return print_graph_entry((struct ftrace_graph_ent_entry *)&saved, s, iter, flags);
> + return print_graph_entry((typeof(field))rfield, s, iter, flags);
> }
> -#endif
> case TRACE_GRAPH_RET: {
> struct ftrace_graph_ret_entry *field;
> trace_assign_type(field, entry);
> --
> 2.34.1
>
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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