[PATCH v11 1/8] function_graph: Support recording and printing the return value of function
Donglin Peng
pengdonglin at sangfor.com.cn
Fri Apr 14 00:44:03 PDT 2023
On 2023/4/8 20:42, Donglin Peng wrote:
> Analyzing system call failures with the function_graph tracer can be a
> time-consuming process, particularly when locating the kernel function
> that first returns an error in the trace logs. This change aims to
> simplify the process by recording the function return value to the
> 'retval' member of 'ftrace_graph_ent' and printing it when outputting
There is a mistake, the retval member is added to ftrace_graph_ret.
> the trace log.
>
> We have introduced new trace options: funcgraph-retval and
> funcgraph-retval-hex. The former controls whether to display the return
> value, while the latter controls the display format.
>
> Please note that even if a function's return type is void, a return
> value will still be printed. You can simply ignore it.
>
> This patch only establishes the fundamental infrastructure. Subsequent
> patches will make this feature available on some commonly used processor
> architectures.
>
> Here is an example:
>
> I attempted to attach the demo process to a cpu cgroup, but it failed:
>
> echo `pidof demo` > /sys/fs/cgroup/cpu/test/tasks
> -bash: echo: write error: Invalid argument
>
> The strace logs indicate that the write system call returned -EINVAL(-22):
> ...
> write(1, "273\n", 4) = -1 EINVAL (Invalid argument)
> ...
>
> To capture trace logs during a write system call, use the following
> commands:
>
> cd /sys/kernel/debug/tracing/
> echo 0 > tracing_on
> echo > trace
> echo *sys_write > set_graph_function
> echo *spin* > set_graph_notrace
> echo *rcu* >> set_graph_notrace
> echo *alloc* >> set_graph_notrace
> echo preempt* >> set_graph_notrace
> echo kfree* >> set_graph_notrace
> echo $$ > set_ftrace_pid
> echo function_graph > current_tracer
> echo 1 > options/funcgraph-retval
> echo 0 > options/funcgraph-retval-hex
> echo 1 > tracing_on
> echo `pidof demo` > /sys/fs/cgroup/cpu/test/tasks
> echo 0 > tracing_on
> cat trace > ~/trace.log
>
> To locate the root cause, search for error code -22 directly in the file
> trace.log and identify the first function that returned -22. Once you
> have identified this function, examine its code to determine the root
> cause.
>
> For example, in the trace log below, cpu_cgroup_can_attach
> returned -22 first, so we can focus our analysis on this function to
> identify the root cause.
>
> ...
>
> 1) | cgroup_migrate() {
> 1) 0.651 us | cgroup_migrate_add_task(); /* = 0xffff93fcfd346c00 */
> 1) | cgroup_migrate_execute() {
> 1) | cpu_cgroup_can_attach() {
> 1) | cgroup_taskset_first() {
> 1) 0.732 us | cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */
> 1) 1.232 us | } /* cgroup_taskset_first = 0xffff93fc8fb20000 */
> 1) 0.380 us | sched_rt_can_attach(); /* = 0x0 */
> 1) 2.335 us | } /* cpu_cgroup_can_attach = -22 */
> 1) 4.369 us | } /* cgroup_migrate_execute = -22 */
> 1) 7.143 us | } /* cgroup_migrate = -22 */
>
> ...
>
> Tested-by: Florian Kauer <florian.kauer at linutronix.de>
> Acked-by: Masami Hiramatsu (Google) <mhiramat at kernel.org>
> Signed-off-by: Donglin Peng <pengdonglin at sangfor.com.cn>
> ---
> v11:
> - Update the Kconfig for FUNCTION_GRAPH_RETVAL.
>
> v9:
> - Update comments for ftrace_return_to_handler
>
> v8:
> - Add some comments on CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
> - Make CONFIG_FUNCTION_GRAPH_RETVAL switable
>
> v7:
> - Rename trace option 'graph_retval_hex' to 'funcgraph-retval-hex'
> - Separate each architecture modification info individual patches
> - Introduce a new structure fgraph_ret_regs for each architecture to
> hold return registers
>
> v6:
> - Remove the conversion code for short and char types, because these
> two types are rarely used to store an error code.
>
> v5:
> - Pass both the return values to ftrace_return_to_handler
> - Modify the parameter sequence of ftrace_return_to_handler to
> decrease the modification of assembly code, thanks to Russell King
> - Wrap __ftrace_return_to_handler with ftrace_return_to_handler
> for compatible
>
> v4:
> - Modify commit message
> - Introduce new option graph_retval_hex to control display format
> - Introduce macro CONFIG_FUNCTION_GRAPH_RETVAL and
> CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
> - Add related arch maintainers to review
>
> v3:
> - Modify the commit message: add trace logs processed with the btf tool
>
> v2:
> - Modify the commit message: use BTF to get the return type of function
> ---
> include/linux/ftrace.h | 3 +
> kernel/trace/Kconfig | 15 +++++
> kernel/trace/fgraph.c | 23 ++++++-
> kernel/trace/trace.h | 2 +
> kernel/trace/trace_entries.h | 26 ++++++++
> kernel/trace/trace_functions_graph.c | 93 +++++++++++++++++++++++++---
> 6 files changed, 151 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 402fc061de75..7639a70e17c1 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -1032,6 +1032,9 @@ struct ftrace_graph_ent {
> */
> struct ftrace_graph_ret {
> unsigned long func; /* Current function */
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> + unsigned long retval;
> +#endif
> int depth;
> /* Number of functions that overran the depth limit for current task */
> unsigned int overrun;
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index a856d4a34c67..fb73a43be261 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -31,6 +31,9 @@ config HAVE_FUNCTION_GRAPH_TRACER
> help
> See Documentation/trace/ftrace-design.rst
>
> +config HAVE_FUNCTION_GRAPH_RETVAL
> + bool
> +
> config HAVE_DYNAMIC_FTRACE
> bool
> help
> @@ -227,6 +230,18 @@ config FUNCTION_GRAPH_TRACER
> the return value. This is done by setting the current return
> address on the current task structure into a stack of calls.
>
> +config FUNCTION_GRAPH_RETVAL
> + bool "Kernel Function Graph Return Value"
> + depends on HAVE_FUNCTION_GRAPH_RETVAL
> + depends on FUNCTION_GRAPH_TRACER
> + default n
> + help
> + Support recording and printing the function return value when
> + using function graph tracer. It can be helpful to locate functions
> + that return errors. This feature is off by default, and you can
> + enable it via the trace option funcgraph-retval.
> + See Documentation/trace/ftrace.rst
> +
> config DYNAMIC_FTRACE
> bool "enable/disable function tracing dynamically"
> depends on FUNCTION_TRACER
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index 218cd95bf8e4..170ec9429efb 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -240,12 +240,16 @@ static struct notifier_block ftrace_suspend_notifier = {
> * Send the trace to the ring-buffer.
> * @return the original return address.
> */
> -unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
> +static unsigned long __ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs,
> + unsigned long frame_pointer)
> {
> struct ftrace_graph_ret trace;
> unsigned long ret;
>
> ftrace_pop_return_trace(&trace, &ret, frame_pointer);
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> + trace.retval = fgraph_ret_regs_return_value(ret_regs);
> +#endif
> trace.rettime = trace_clock_local();
> ftrace_graph_return(&trace);
> /*
> @@ -266,6 +270,23 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
> return ret;
> }
>
> +/*
> + * After all architecures have selected HAVE_FUNCTION_GRAPH_RETVAL, we can
> + * leave only ftrace_return_to_handler(ret_regs).
> + */
> +#ifdef CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
> +unsigned long ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs)
> +{
> + return __ftrace_return_to_handler(ret_regs,
> + fgraph_ret_regs_frame_pointer(ret_regs));
> +}
> +#else
> +unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
> +{
> + return __ftrace_return_to_handler(NULL, frame_pointer);
> +}
> +#endif
> +
> /**
> * ftrace_graph_get_ret_stack - return the entry of the shadow stack
> * @task: The task to read the shadow stack from
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 616e1aa1c4da..0a3c4582df10 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -831,6 +831,8 @@ static __always_inline bool ftrace_hash_empty(struct ftrace_hash *hash)
> #define TRACE_GRAPH_PRINT_TAIL 0x100
> #define TRACE_GRAPH_SLEEP_TIME 0x200
> #define TRACE_GRAPH_GRAPH_TIME 0x400
> +#define TRACE_GRAPH_PRINT_RETVAL 0x800
> +#define TRACE_GRAPH_PRINT_RETVAL_HEX 0x1000
> #define TRACE_GRAPH_PRINT_FILL_SHIFT 28
> #define TRACE_GRAPH_PRINT_FILL_MASK (0x3 << TRACE_GRAPH_PRINT_FILL_SHIFT)
>
> diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
> index cd41e863b51c..340b2fa98218 100644
> --- a/kernel/trace/trace_entries.h
> +++ b/kernel/trace/trace_entries.h
> @@ -86,6 +86,30 @@ FTRACE_ENTRY_PACKED(funcgraph_entry, ftrace_graph_ent_entry,
> );
>
> /* Function return entry */
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +
> +FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
> +
> + TRACE_GRAPH_RET,
> +
> + F_STRUCT(
> + __field_struct( struct ftrace_graph_ret, ret )
> + __field_packed( unsigned long, ret, func )
> + __field_packed( unsigned long, ret, retval )
> + __field_packed( int, ret, depth )
> + __field_packed( unsigned int, ret, overrun )
> + __field_packed( unsigned long long, ret, calltime)
> + __field_packed( unsigned long long, ret, rettime )
> + ),
> +
> + F_printk("<-- %ps (%d) (start: %llx end: %llx) over: %d retval: %lx",
> + (void *)__entry->func, __entry->depth,
> + __entry->calltime, __entry->rettime,
> + __entry->depth, __entry->retval)
> +);
> +
> +#else
> +
> FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
>
> TRACE_GRAPH_RET,
> @@ -105,6 +129,8 @@ FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
> __entry->depth)
> );
>
> +#endif
> +
> /*
> * Context switch trace entry - which task (and prio) we switched from/to:
> *
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 203204cadf92..c35fbaab2a47 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -58,6 +58,12 @@ static struct tracer_opt trace_opts[] = {
> { TRACER_OPT(funcgraph-irqs, TRACE_GRAPH_PRINT_IRQS) },
> /* Display function name after trailing } */
> { TRACER_OPT(funcgraph-tail, TRACE_GRAPH_PRINT_TAIL) },
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> + /* Display function return value ? */
> + { TRACER_OPT(funcgraph-retval, TRACE_GRAPH_PRINT_RETVAL) },
> + /* Display function return value in hexadecimal format ? */
> + { TRACER_OPT(funcgraph-retval-hex, TRACE_GRAPH_PRINT_RETVAL_HEX) },
> +#endif
> /* Include sleep time (scheduled out) between entry and return */
> { TRACER_OPT(sleep-time, TRACE_GRAPH_SLEEP_TIME) },
>
> @@ -619,6 +625,56 @@ print_graph_duration(struct trace_array *tr, unsigned long long duration,
> trace_seq_puts(s, "| ");
> }
>
> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
> +
> +#define __TRACE_GRAPH_PRINT_RETVAL TRACE_GRAPH_PRINT_RETVAL
> +
> +static void print_graph_retval(struct trace_seq *s, unsigned long retval,
> + bool leaf, void *func, bool hex_format)
> +{
> + unsigned long err_code = 0;
> +
> + if (retval == 0 || hex_format)
> + goto done;
> +
> + /* Check if the return value matches the negative format */
> + if (IS_ENABLED(CONFIG_64BIT) && (retval & BIT(31)) &&
> + (((u64)retval) >> 32) == 0) {
> + /* sign extension */
> + err_code = (unsigned long)(s32)retval;
> + } else {
> + err_code = retval;
> + }
> +
> + if (!IS_ERR_VALUE(err_code))
> + err_code = 0;
> +
> +done:
> + if (leaf) {
> + if (hex_format || (err_code == 0))
> + trace_seq_printf(s, "%ps(); /* = 0x%lx */\n",
> + func, retval);
> + else
> + trace_seq_printf(s, "%ps(); /* = %ld */\n",
> + func, err_code);
> + } else {
> + if (hex_format || (err_code == 0))
> + trace_seq_printf(s, "} /* %ps = 0x%lx */\n",
> + func, retval);
> + else
> + trace_seq_printf(s, "} /* %ps = %ld */\n",
> + func, err_code);
> + }
> +}
> +
> +#else
> +
> +#define __TRACE_GRAPH_PRINT_RETVAL 0
> +
> +#define print_graph_retval(_seq, _retval, _leaf, _func, _format) do {} while (0)
> +
> +#endif
> +
> /* Case of a leaf function on its call entry */
> static enum print_line_t
> print_graph_entry_leaf(struct trace_iterator *iter,
> @@ -663,7 +719,15 @@ print_graph_entry_leaf(struct trace_iterator *iter,
> for (i = 0; i < call->depth * TRACE_GRAPH_INDENT; i++)
> trace_seq_putc(s, ' ');
>
> - trace_seq_printf(s, "%ps();\n", (void *)call->func);
> + /*
> + * Write out the function return value if the option function-retval is
> + * enabled.
> + */
> + if (flags & __TRACE_GRAPH_PRINT_RETVAL)
> + print_graph_retval(s, graph_ret->retval, true, (void *)call->func,
> + !!(flags & TRACE_GRAPH_PRINT_RETVAL_HEX));
> + else
> + trace_seq_printf(s, "%ps();\n", (void *)call->func);
>
> print_graph_irq(iter, graph_ret->func, TRACE_GRAPH_RET,
> cpu, iter->ent->pid, flags);
> @@ -942,16 +1006,25 @@ print_graph_return(struct ftrace_graph_ret *trace, struct trace_seq *s,
> trace_seq_putc(s, ' ');
>
> /*
> - * If the return function does not have a matching entry,
> - * then the entry was lost. Instead of just printing
> - * the '}' and letting the user guess what function this
> - * belongs to, write out the function name. Always do
> - * that if the funcgraph-tail option is enabled.
> + * Always write out the function name and its return value if the
> + * function-retval option is enabled.
> */
> - if (func_match && !(flags & TRACE_GRAPH_PRINT_TAIL))
> - trace_seq_puts(s, "}\n");
> - else
> - trace_seq_printf(s, "} /* %ps */\n", (void *)trace->func);
> + if (flags & __TRACE_GRAPH_PRINT_RETVAL) {
> + print_graph_retval(s, trace->retval, false, (void *)trace->func,
> + !!(flags & TRACE_GRAPH_PRINT_RETVAL_HEX));
> + } else {
> + /*
> + * If the return function does not have a matching entry,
> + * then the entry was lost. Instead of just printing
> + * the '}' and letting the user guess what function this
> + * belongs to, write out the function name. Always do
> + * that if the funcgraph-tail option is enabled.
> + */
> + if (func_match && !(flags & TRACE_GRAPH_PRINT_TAIL))
> + trace_seq_puts(s, "}\n");
> + else
> + trace_seq_printf(s, "} /* %ps */\n", (void *)trace->func);
> + }
>
> /* Overrun */
> if (flags & TRACE_GRAPH_PRINT_OVERRUN)
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