@@ -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;
@@ -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 "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
@@ -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
@@ -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)
@@ -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:
*
@@ -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)
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 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@linutronix.de> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Signed-off-by: Donglin Peng <pengdonglin@sangfor.com.cn> --- 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(-)