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function_graph: Support recording and printing the return value of function 

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_ret' and printing it when outputting
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 */

...

Link: https://lkml.kernel.org/r/1fc502712c981e0e6742185ba242992170ac9da8.1680954589.git.pengdonglin@sangfor.com.cn

Tested-by: Florian Kauer <florian.kauer@linutronix.de>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Donglin Peng <pengdonglin@sangfor.com.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Donglin Peng 2023-04-08 05:42:15 -07:00 committed by Steven Rostedt (Google)
parent f3d40e6545
commit a1be9ccc57
6 changed files with 151 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/ftrace.h
View File

@ -1018,6 +1018,9 @@ 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;

15
kernel/trace/Kconfig
View File

@ -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

23
kernel/trace/fgraph.c
View File

@ -243,12 +243,16 @@ struct fgraph_ret_regs;
* 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);
/*
@ -269,6 +273,23 @@ 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

2
kernel/trace/trace.h
View File

@ -832,6 +832,8 @@ 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)

26
kernel/trace/trace_entries.h
View File

@ -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:
*

93
kernel/trace/trace_functions_graph.c
View File

@ -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)