[RFC PATCH v3] ftrace: support very early function tracing

* [RFC PATCH v3] ftrace: support very early function tracing
@ 2018-10-24 19:22 Abderrahmane Benbachir
  2018-11-30  6:13 ` Abderrahmane Benbachir
  2018-11-30 17:20 ` Steven Rostedt
  0 siblings, 2 replies; 3+ messages in thread
From: Abderrahmane Benbachir @ 2018-10-24 19:22 UTC (permalink / raw)
  To: rostedt; +Cc: linux-kernel, peterz, mingo, mathieu.desnoyers


Hi Steve,
I believe this patch is quite stable. I know some folks that were using
it to debug early VM/KVM handshak and seemed very helpful for them.


Previous changes:

PATCH v1: Initial patch

PATCH v2:

   Removed arch specific code and use the default clock.
   Add more code re-usability
   Add HAVE_VERY_EARLY_FTRACE config option which is disabled by default


PATCH v3 starts here :
---------------------------------------------------------------------

The very early tracing will start from the beginning of start_kernel()
and will stop at ftrace_init()

start_kernel()
{
   ftrace_early_init() <--- start early function tracing
   ...
   (calls)
   ...
   ftrace_init()       <--- stop early function tracing
   early_trace_init(); <--- fill ring buffer, before starting function tracer
   ...
}

The events are placed in a temporary buffer, which will be copied to
the trace buffer after memory setup.

Dynamic tracing is not implemented with live patching, we use
ftrace_filter and ftrace_notrace to find which functions to be
filtered (traced / not traced), then during the callback from
mcount hook, we do binary search lookup to decide which function
to be save or not.

Signed-off-by: Abderrahmane Benbachir <abderrahmane.benbachir@polymtl.ca>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: linux-kernel@vger.kernel.org
---
  arch/x86/Kconfig            |   1 +
  arch/x86/kernel/ftrace_32.S |  45 ++++--
  arch/x86/kernel/ftrace_64.S |  14 ++
  include/linux/ftrace.h      |  16 +-
  init/main.c                 |   1 +
  kernel/trace/Kconfig        |  51 +++++++
  kernel/trace/ftrace.c       | 289 +++++++++++++++++++++++++++++++++++-
  kernel/trace/trace.c        |   3 +
  8 files changed, 408 insertions(+), 12 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1a0be022f91d..3d5b89061a51 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -148,6 +148,7 @@ config X86
  	select HAVE_FENTRY			if X86_64 || DYNAMIC_FTRACE
  	select HAVE_FTRACE_MCOUNT_RECORD
  	select HAVE_FUNCTION_GRAPH_TRACER
+	select HAVE_VERY_EARLY_FTRACE
  	select HAVE_FUNCTION_TRACER
  	select HAVE_GCC_PLUGINS
  	select HAVE_HW_BREAKPOINT
diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S
index 4c8440de3355..1f2889d9e37e 100644
--- a/arch/x86/kernel/ftrace_32.S
+++ b/arch/x86/kernel/ftrace_32.S
@@ -31,12 +31,8 @@ EXPORT_SYMBOL(mcount)
  # define MCOUNT_FRAME			0	/* using frame = false */
  #endif

-ENTRY(function_hook)
-	ret
-END(function_hook)
-
-ENTRY(ftrace_caller)

+.macro save_mcount_regs
  #ifdef USING_FRAME_POINTER
  # ifdef CC_USING_FENTRY
  	/*
@@ -73,11 +69,9 @@ ENTRY(ftrace_caller)

  	movl	function_trace_op, %ecx
  	subl	$MCOUNT_INSN_SIZE, %eax
+	.endm

-.globl ftrace_call
-ftrace_call:
-	call	ftrace_stub
-
+.macro restore_mcount_regs
  	addl	$4, %esp			/* skip NULL pointer */
  	popl	%edx
  	popl	%ecx
@@ -90,6 +84,39 @@ ftrace_call:
  	addl	$4, %esp			/* skip parent ip */
  # endif
  #endif
+	.endm
+
+ENTRY(function_hook)
+#ifdef CONFIG_VERY_EARLY_FUNCTION_TRACER
+	cmpl	$__PAGE_OFFSET, %esp
+	jb	vearly_stub			/* Paging not enabled yet? */
+
+	cmpl	$ftrace_stub, ftrace_vearly_trace_function
+	jnz vearly_trace
+
+vearly_stub:
+	ret
+
+vearly_trace:
+	save_mcount_regs
+	call	*ftrace_vearly_trace_function
+	restore_mcount_regs
+
+	jmp vearly_stub
+#else
+	ret
+#endif
+END(function_hook)
+
+ENTRY(ftrace_caller)
+	save_mcount_regs
+
+.globl ftrace_call
+ftrace_call:
+	call	ftrace_stub
+
+	restore_mcount_regs
+
  .Lftrace_ret:
  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
  .globl ftrace_graph_call
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 91b2cff4b79a..879db2c759e3 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -151,7 +151,21 @@ EXPORT_SYMBOL(mcount)
  #ifdef CONFIG_DYNAMIC_FTRACE

  ENTRY(function_hook)
+#ifdef CONFIG_VERY_EARLY_FUNCTION_TRACER
+	cmpq $ftrace_stub, ftrace_vearly_trace_function
+	jnz vearly_trace
+
+vearly_stub:
  	retq
+
+vearly_trace:
+	save_mcount_regs
+	call *ftrace_vearly_trace_function
+	restore_mcount_regs
+	jmp vearly_stub
+#else
+	retq
+#endif
  ENDPROC(function_hook)

  ENTRY(ftrace_caller)
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index a397907e8d72..78e023c61289 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -239,6 +239,16 @@ static inline void ftrace_free_init_mem(void) { }
  static inline void ftrace_free_mem(struct module *mod, void *start,  
void *end) { }
  #endif /* CONFIG_FUNCTION_TRACER */

+#ifdef CONFIG_VERY_EARLY_FUNCTION_TRACER
+extern void ftrace_early_init(char *command_line);
+extern void ftrace_early_shutdown(void);
+extern void ftrace_early_fill_ringbuffer(void *data);
+#else
+static inline void ftrace_early_init(char *command_line) { }
+static inline void ftrace_early_shutdown(void) { }
+static inline void ftrace_early_fill_ringbuffer(void *data) { }
+#endif
+
  #ifdef CONFIG_STACK_TRACER

  #define STACK_TRACE_ENTRIES 500
@@ -443,6 +453,10 @@ unsigned long ftrace_get_addr_curr(struct  
dyn_ftrace *rec);

  extern ftrace_func_t ftrace_trace_function;

+#if defined(CONFIG_VERY_EARLY_FUNCTION_TRACER) &&  
defined(CONFIG_DYNAMIC_FTRACE)
+extern ftrace_func_t ftrace_vearly_trace_function;
+#endif
+
  int ftrace_regex_open(struct ftrace_ops *ops, int flag,
  		  struct inode *inode, struct file *file);
  ssize_t ftrace_filter_write(struct file *file, const char __user *ubuf,
@@ -716,7 +730,7 @@ static inline unsigned long get_lock_parent_ip(void)
  #ifdef CONFIG_FTRACE_MCOUNT_RECORD
  extern void ftrace_init(void);
  #else
-static inline void ftrace_init(void) { }
+static inline void ftrace_init(void) { ftrace_early_shutdown(); }
  #endif

  /*
diff --git a/init/main.c b/init/main.c
index 18f8f0140fa0..1b289325223f 100644
--- a/init/main.c
+++ b/init/main.c
@@ -533,6 +533,7 @@ asmlinkage __visible void __init start_kernel(void)
  	char *command_line;
  	char *after_dashes;

+	ftrace_early_init(boot_command_line);
  	set_task_stack_end_magic(&init_task);
  	smp_setup_processor_id();
  	debug_objects_early_init();
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 5e3de28c7677..4b358bf6abb0 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -19,6 +19,11 @@ config HAVE_FUNCTION_TRACER
  	help
  	  See Documentation/trace/ftrace-design.rst

+config HAVE_VERY_EARLY_FTRACE
+	bool
+	help
+	  See Documentation/trace/ftrace-design.txt
+
  config HAVE_FUNCTION_GRAPH_TRACER
  	bool
  	help
@@ -155,6 +160,52 @@ config FUNCTION_TRACER
  	  (the bootup default), then the overhead of the instructions is very
  	  small and not measurable even in micro-benchmarks.

+config VERY_EARLY_FUNCTION_TRACER
+	bool "Very Early Kernel Function Tracer"
+	depends on FUNCTION_TRACER
+	depends on HAVE_VERY_EARLY_FTRACE
+	help
+	  Normally, function tracing can only start after memory has been
+	  initialized early in boot. If "ftrace=function" is added to the
+	  command line, then function tracing will start after memory setup.
+	  In order to trace functions before that, this option will
+	  have function tracing starts before memory setup is complete, by
+	  placing the trace in a temporary buffer, which will be copied to
+	  the trace buffer after memory setup. The size of this temporary
+	  buffer is defined by VERY_EARLY_FTRACE_BUF_SHIFT.
+
+config VERY_EARLY_FTRACE_BUF_SHIFT
+	int "Temporary buffer size (17 => 128 KB, 24 => 16 MB)"
+	depends on VERY_EARLY_FUNCTION_TRACER
+	range 8 24
+	default 19
+	help
+	  Select the size of the buffer to be used for storing function calls at
+	  very early stage.
+	  The value defines the size as a power of 2.
+	  Examples:
+	    20 =>   1 MB
+	    19 => 512 KB
+	    17 => 128 KB
+
+config VERY_EARLY_FTRACE_FILTER_SHIFT
+	int "Temporary filter size (filter/notrace) (17 => 128 KB, 19 => 512 KB)"
+	depends on VERY_EARLY_FUNCTION_TRACER
+	depends on FTRACE_MCOUNT_RECORD
+	range 0 19
+	default 17
+	help
+	  Select the size of the filter buffer to be used for filtering (trace/
+	  no trace) functions at very early stage.
+	  Two buffers (trace/no_trace) will be created using by this option.
+	  These following kernel parameters control filtering during bootup :
+	  "ftrace_filter", "ftrace_notrace".
+	  The value defines the size as a power of 2.
+	  Examples:
+	    19 => 512 KB for each buffer
+	    18 => 256 KB for each buffer
+	    17 => 128 KB for each buffer
+
  config FUNCTION_GRAPH_TRACER
  	bool "Kernel Function Graph Tracer"
  	depends on HAVE_FUNCTION_GRAPH_TRACER
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f536f601bd46..45d575ae2056 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -65,6 +65,11 @@
  #define FTRACE_HASH_DEFAULT_BITS 10
  #define FTRACE_HASH_MAX_BITS 12

+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+extern unsigned long __start_mcount_loc[];
+extern unsigned long __stop_mcount_loc[];
+#endif
+
  #ifdef CONFIG_DYNAMIC_FTRACE
  #define INIT_OPS_HASH(opsname)	\
  	.func_hash		= &opsname.local_hash,			\
@@ -6126,11 +6131,11 @@ void __init ftrace_free_init_mem(void)

  void __init ftrace_init(void)
  {
-	extern unsigned long __start_mcount_loc[];
-	extern unsigned long __stop_mcount_loc[];
  	unsigned long count, flags;
  	int ret;

+	ftrace_early_shutdown();
+
  	local_irq_save(flags);
  	ret = ftrace_dyn_arch_init();
  	local_irq_restore(flags);
@@ -7092,3 +7097,283 @@ void ftrace_graph_exit_task(struct task_struct *t)
  	kfree(ret_stack);
  }
  #endif
+
+
+#ifdef CONFIG_VERY_EARLY_FUNCTION_TRACER
+
+#define VEARLY_BUFF_LEN ((1 << CONFIG_VERY_EARLY_FTRACE_BUF_SHIFT) / \
+					sizeof(struct ftrace_vearly_entry))
+
+struct ftrace_vearly_entry {
+	unsigned long ip;
+	unsigned long parent_ip;
+	unsigned long long clock;
+};
+/*
+ * Only CPU0 is running in early stage, no need to have per-cpu buffer
+ */
+static struct ftrace_vearly_entry  
ftrace_vearly_entries[VEARLY_BUFF_LEN] __initdata;
+static const unsigned long VEARLY_BUFF_MAX __initconst = VEARLY_BUFF_LEN;
+static unsigned long vearly_entries_count __initdata;
+static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
+
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+ftrace_func_t ftrace_vearly_trace_function __read_mostly = ftrace_stub;
+#else
+# define ftrace_vearly_trace_function ftrace_trace_function
+#endif
+
+static inline __init void ftrace_vearly_disable(void)
+{
+	ftrace_vearly_trace_function = ftrace_stub;
+}
+
+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+#define VEARLY_FILTER_LEN ((1 << CONFIG_VERY_EARLY_FTRACE_FILTER_SHIFT) / \
+					sizeof(unsigned long))
+struct ftrace_vearly_filtering {
+	unsigned long list[VEARLY_FILTER_LEN];
+	char buf[COMMAND_LINE_SIZE];
+	int size;
+};
+static const unsigned long VEARLY_FILTER_MAX __initconst = VEARLY_FILTER_LEN;
+static struct ftrace_vearly_filtering ftrace_data_notrace __initdata;
+static struct ftrace_vearly_filtering ftrace_data_filter __initdata;
+
+static __init int ftrace_vearly_filter_has_addr(unsigned long addr,
+	unsigned long *filter, int *size)
+{
+	int i;
+
+	for (i = 0; i < *size; i++) {
+		if (filter[i] == addr)
+			return 1;
+	}
+	return 0;
+}
+
+static __init int
+ftrace_vearly_match_record(unsigned long ip, struct ftrace_glob *func_g)
+{
+	char str[KSYM_SYMBOL_LEN];
+	char *modname;
+
+	kallsyms_lookup(ip, NULL, NULL, &modname, str);
+	return ftrace_match(str, func_g);
+}
+
+static __init void
+ftrace_vearly_regex(char *func, unsigned long *filter, int *size)
+{
+	struct ftrace_glob func_g = { .type = MATCH_FULL };
+	unsigned long *start = __start_mcount_loc;
+	unsigned long *end = __stop_mcount_loc;
+	unsigned long count;
+	unsigned long addr;
+	unsigned long *p;
+	int clear_filter = 0;
+
+	count = end - start;
+
+	if (!count)
+		return;
+
+	if (func) {
+		func_g.type = filter_parse_regex(func, strlen(func), &func_g.search,
+						 &clear_filter);
+		func_g.len = strlen(func_g.search);
+	}
+
+	p = start;
+	while (p < end) {
+		addr = ftrace_call_adjust(*p++);
+		if (!addr)
+			continue;
+
+		if ((*size) > VEARLY_FILTER_MAX)
+			return;
+
+		if (ftrace_vearly_match_record(addr, &func_g)) {
+			if (!ftrace_vearly_filter_has_addr(addr, filter, size))
+				filter[(*size)++] = addr;
+		}
+	}
+}
+
+static int __init ftrace_addr_compare(const void *a, const void *b)
+{
+	if (*(unsigned long *)a > *(unsigned long *)b)
+		return 1;
+	if (*(unsigned long *)a < *(unsigned long *)b)
+		return -1;
+
+	return 0;
+}
+
+static void __init ftrace_addr_swap(void *a, void *b, int size)
+{
+	unsigned long t = *(unsigned long *)a;
+	*(unsigned long *)a = *(unsigned long *)b;
+	*(unsigned long *)b = t;
+}
+
+static __init int set_ftrace_vearly_filtering(void *data, char *str)
+{
+	struct ftrace_vearly_filtering *ftrace_data = data;
+	char *func;
+	char *buf;
+
+	if (!ftrace_data)
+		return 0;
+	buf = ftrace_data->buf;
+	strlcpy(buf, str, COMMAND_LINE_SIZE);
+
+	while (buf) {
+		func = strsep(&buf, ",");
+		ftrace_vearly_regex(func, ftrace_data->list, &ftrace_data->size);
+	}
+	/* sort filter to use binary search on it */
+	sort(ftrace_data->list, ftrace_data->size,
+		sizeof(unsigned long), ftrace_addr_compare, ftrace_addr_swap);
+
+	return 1;
+}
+
+#define ftrace_vearly_bsearch_addr(addr, data) bsearch(&addr, data.list,\
+	data.size, sizeof(unsigned long), ftrace_addr_compare)
+
+#endif /* CONFIG_FTRACE_MCOUNT_RECORD */
+
+
+static __init void
+ftrace_function_vearly_trace_call(unsigned long ip, unsigned long parent_ip,
+			struct ftrace_ops *op, struct pt_regs *regs)
+{
+	struct ftrace_vearly_entry *entry;
+
+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+	if (ftrace_data_notrace.size &&
+			ftrace_vearly_bsearch_addr(ip, ftrace_data_notrace))
+		return;
+
+	if (ftrace_data_filter.size &&
+			!ftrace_vearly_bsearch_addr(ip, ftrace_data_filter))
+		return;
+#endif
+
+	if (vearly_entries_count >= VEARLY_BUFF_MAX) {
+		/* stop tracing when buffer is full */
+		ftrace_vearly_disable();
+		return;
+	}
+
+	entry = &ftrace_vearly_entries[vearly_entries_count++];
+	entry->ip = ip;
+	entry->parent_ip = parent_ip;
+	entry->clock = trace_clock_local();
+}
+
+/*
+ * Will be passed to ringbuffer by early_trace_clock
+ */
+static u64 early_timestamp __initdata;
+
+static __init u64 early_trace_clock(void)
+{
+	return early_timestamp;
+}
+
+void __init ftrace_early_fill_ringbuffer(void *data)
+{
+	struct ftrace_vearly_entry *entry;
+	struct trace_array *tr = data;
+	int i;
+
+	if (ftrace_vearly_entries <= 0)
+		return;
+
+	ring_buffer_set_clock(tr->trace_buffer.buffer, early_trace_clock);
+	preempt_disable_notrace();
+	for (i = 0; i < vearly_entries_count; i++) {
+		entry = &ftrace_vearly_entries[i];
+		early_timestamp = entry->clock;
+		trace_function(tr, entry->ip, entry->parent_ip, 0, 0);
+	}
+	preempt_enable_notrace();
+	ring_buffer_set_clock(tr->trace_buffer.buffer, trace_clock_local);
+}
+
+/*
+ * this will be used as __setup_param
+ */
+struct ftrace_vearly_obs_param {
+	int (*setup_func)(void *, char*);
+	const char *str;
+	void *data;
+};
+static struct ftrace_vearly_obs_param ftrace_vearly_params[] __initdata = {
+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+	{
+		.str = "ftrace_notrace",
+		.data = &ftrace_data_notrace,
+		.setup_func = set_ftrace_vearly_filtering,
+	},
+	{
+		.str = "ftrace_filter",
+		.data = &ftrace_data_filter,
+		.setup_func = set_ftrace_vearly_filtering,
+	},
+#endif
+};
+
+static int __init ftrace_do_very_early_param(char *param, char *val,
+				 const char *unused, void *arg)
+{
+	int size = ARRAY_SIZE(ftrace_vearly_params);
+	struct ftrace_vearly_obs_param *p;
+	int i;
+
+	for (i = 0; i < size; i++) {
+		p = &ftrace_vearly_params[i];
+		if (strcmp(param, p->str) == 0) {
+			p->setup_func(p->data, val);
+			return 0;
+		}
+	}
+	return 0;
+}
+
+void __init ftrace_early_init(char *command_line)
+{
+	/* proceed only if function tracing was enabled */
+	if (!strstr(command_line, "ftrace=function "))
+		return;
+
+	strlcpy(tmp_cmdline, command_line, COMMAND_LINE_SIZE);
+	parse_args("ftrace vearly options", tmp_cmdline, NULL, 0, 0, 0, NULL,
+		ftrace_do_very_early_param);
+
+	// After this point, we enable early function tracing
+	ftrace_vearly_trace_function = ftrace_function_vearly_trace_call;
+}
+
+void __init ftrace_early_shutdown(void)
+{
+	if (ftrace_vearly_trace_function == ftrace_stub)
+		return;
+
+	// Disable early tracing
+	ftrace_vearly_disable();
+
+#ifdef CONFIG_FTRACE_MCOUNT_RECORD
+	pr_info("ftrace: vearly %lu entries, notrace=%d, filter=%d",
+		vearly_entries_count,
+		ftrace_data_notrace.size,
+		ftrace_data_filter.size);
+#else
+	pr_info("ftrace: vearly %lu recorded entries", vearly_entries_count);
+#endif
+}
+
+#endif /* CONFIG_VERY_EARLY_FUNCTION_TRACER */
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index bf6f1d70484d..08763c380a3e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8551,6 +8551,9 @@ __init static int tracer_alloc_buffers(void)
  	/* Function tracing may start here (via kernel command line) */
  	init_function_trace();

+	/* Pre-fill the ring buffer with very early events */
+	ftrace_early_fill_ringbuffer(&global_trace);
+
  	/* All seems OK, enable tracing */
  	tracing_disabled = 0;

-- 
2.17.1




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