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Message-ID: <CAErzpmsHNRzB2pBFVSAG4ii=VN98NEtehEbnYNQY-4TBWgM3ag@mail.gmail.com>
Date: Wed, 12 Nov 2025 14:03:30 +0800
From: Donglin Peng <dolinux.peng@...il.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
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>
Subject: Re: [PATCH v3 RESEND] function_graph: Enable funcgraph-args and
funcgraph-retaddr to work simultaneously
On Wed, Nov 12, 2025 at 1:17 PM Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> 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 for ack.
>
> 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.
Thanks. I added the else braces for consistency with the
multi-statement if branch,
per coding-style.rst. Happy to remove if you prefer the
single-statement exception.
https://elixir.bootlin.com/linux/v6.18-rc5/source/Documentation/process/coding-style.rst#L213
Do not unnecessarily use braces where a single statement will do.
.. code-block:: c
if (condition)
action();
and
.. code-block:: c
if (condition)
do_this();
else
do_that();
This does not apply if only one branch of a conditional statement is a single
statement; in the latter case use braces in both branches:
.. code-block:: c
if (condition) {
do_this();
do_that();
} else {
otherwise();
}
>
> > 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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