ftrace: use dynamic patching for updating mcount calls
This patch replaces the indirect call to the mcount function
pointer with a direct call that will be patched by the
dynamic ftrace routines.
On boot up, the mcount function calls the ftace_stub function.
When the dynamic ftrace code is initialized, the ftrace_stub
is replaced with a call to the ftrace_record_ip, which records
the instruction pointers of the locations that call it.
Later, the ftraced daemon will call kstop_machine and patch all
the locations to nops.
When a ftrace is enabled, the original calls to mcount will now
be set top call ftrace_caller, which will do a direct call
to the registered ftrace function. This direct call is also patched
when the function that should be called is updated.
All patching is performed by a kstop_machine routine to prevent any
type of race conditions that is associated with modifying code
on the fly.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f6d9af3b..88544f9 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -26,14 +26,8 @@
#include "trace.h"
-#ifdef CONFIG_DYNAMIC_FTRACE
-# define FTRACE_ENABLED_INIT 1
-#else
-# define FTRACE_ENABLED_INIT 0
-#endif
-
-int ftrace_enabled = FTRACE_ENABLED_INIT;
-static int last_ftrace_enabled = FTRACE_ENABLED_INIT;
+int ftrace_enabled;
+static int last_ftrace_enabled;
static DEFINE_SPINLOCK(ftrace_lock);
static DEFINE_MUTEX(ftrace_sysctl_lock);
@@ -149,6 +143,14 @@
#ifdef CONFIG_DYNAMIC_FTRACE
+enum {
+ FTRACE_ENABLE_CALLS = (1 << 0),
+ FTRACE_DISABLE_CALLS = (1 << 1),
+ FTRACE_UPDATE_TRACE_FUNC = (1 << 2),
+ FTRACE_ENABLE_MCOUNT = (1 << 3),
+ FTRACE_DISABLE_MCOUNT = (1 << 4),
+};
+
static struct hlist_head ftrace_hash[FTRACE_HASHSIZE];
static DEFINE_PER_CPU(int, ftrace_shutdown_disable_cpu);
@@ -199,12 +201,8 @@
hlist_add_head(&node->node, &ftrace_hash[key]);
}
-static notrace struct dyn_ftrace *ftrace_alloc_shutdown_node(unsigned long ip)
+static notrace struct dyn_ftrace *ftrace_alloc_dyn_node(unsigned long ip)
{
- /* If this was already converted, skip it */
- if (ftrace_ip_converted(ip))
- return NULL;
-
if (ftrace_pages->index == ENTRIES_PER_PAGE) {
if (!ftrace_pages->next)
return NULL;
@@ -215,7 +213,7 @@
}
static void notrace
-ftrace_record_ip(unsigned long ip, unsigned long parent_ip)
+ftrace_record_ip(unsigned long ip)
{
struct dyn_ftrace *node;
unsigned long flags;
@@ -223,6 +221,9 @@
int resched;
int atomic;
+ if (!ftrace_enabled)
+ return;
+
resched = need_resched();
preempt_disable_notrace();
@@ -251,11 +252,12 @@
/*
* There's a slight race that the ftraced will update the
- * hash and reset here. The arch alloc is responsible
- * for seeing if the IP has already changed, and if
- * it has, the alloc will fail.
+ * hash and reset here. If it is already converted, skip it.
*/
- node = ftrace_alloc_shutdown_node(ip);
+ if (ftrace_ip_converted(ip))
+ goto out_unlock;
+
+ node = ftrace_alloc_dyn_node(ip);
if (!node)
goto out_unlock;
@@ -277,11 +279,7 @@
preempt_enable_notrace();
}
-static struct ftrace_ops ftrace_shutdown_ops __read_mostly =
-{
- .func = ftrace_record_ip,
-};
-
+#define FTRACE_ADDR ((long)(&ftrace_caller))
#define MCOUNT_ADDR ((long)(&mcount))
static void notrace ftrace_replace_code(int saved)
@@ -309,9 +307,9 @@
ip = rec->ip;
if (saved)
- new = ftrace_call_replace(ip, MCOUNT_ADDR);
+ new = ftrace_call_replace(ip, FTRACE_ADDR);
else
- old = ftrace_call_replace(ip, MCOUNT_ADDR);
+ old = ftrace_call_replace(ip, FTRACE_ADDR);
failed = ftrace_modify_code(ip, old, new);
if (failed)
@@ -320,16 +318,6 @@
}
}
-static notrace void ftrace_startup_code(void)
-{
- ftrace_replace_code(1);
-}
-
-static notrace void ftrace_shutdown_code(void)
-{
- ftrace_replace_code(0);
-}
-
static notrace void ftrace_shutdown_replenish(void)
{
if (ftrace_pages->next)
@@ -339,16 +327,8 @@
ftrace_pages->next = (void *)get_zeroed_page(GFP_KERNEL);
}
-static int notrace __ftrace_modify_code(void *data)
-{
- void (*func)(void) = data;
-
- func();
- return 0;
-}
-
static notrace void
-ftrace_code_disable(struct dyn_ftrace *rec, unsigned long addr)
+ftrace_code_disable(struct dyn_ftrace *rec)
{
unsigned long ip;
unsigned char *nop, *call;
@@ -357,67 +337,113 @@
ip = rec->ip;
nop = ftrace_nop_replace();
- call = ftrace_call_replace(ip, addr);
+ call = ftrace_call_replace(ip, MCOUNT_ADDR);
failed = ftrace_modify_code(ip, call, nop);
if (failed)
rec->flags |= FTRACE_FL_FAILED;
}
-static void notrace ftrace_run_startup_code(void)
+static int notrace __ftrace_modify_code(void *data)
{
- stop_machine_run(__ftrace_modify_code, ftrace_startup_code, NR_CPUS);
+ unsigned long addr;
+ int *command = data;
+
+ if (*command & FTRACE_ENABLE_CALLS)
+ ftrace_replace_code(1);
+ else if (*command & FTRACE_DISABLE_CALLS)
+ ftrace_replace_code(0);
+
+ if (*command & FTRACE_UPDATE_TRACE_FUNC)
+ ftrace_update_ftrace_func(ftrace_trace_function);
+
+ if (*command & FTRACE_ENABLE_MCOUNT) {
+ addr = (unsigned long)ftrace_record_ip;
+ ftrace_mcount_set(&addr);
+ } else if (*command & FTRACE_DISABLE_MCOUNT) {
+ addr = (unsigned long)ftrace_stub;
+ ftrace_mcount_set(&addr);
+ }
+
+ return 0;
}
-static void notrace ftrace_run_shutdown_code(void)
+static void notrace ftrace_run_update_code(int command)
{
- stop_machine_run(__ftrace_modify_code, ftrace_shutdown_code, NR_CPUS);
+ stop_machine_run(__ftrace_modify_code, &command, NR_CPUS);
}
+static ftrace_func_t saved_ftrace_func;
+
static void notrace ftrace_startup(void)
{
+ int command = 0;
+
mutex_lock(&ftraced_lock);
ftraced_suspend++;
- if (ftraced_suspend != 1)
- goto out;
- __unregister_ftrace_function(&ftrace_shutdown_ops);
+ if (ftraced_suspend == 1)
+ command |= FTRACE_ENABLE_CALLS;
- if (ftrace_enabled)
- ftrace_run_startup_code();
+ if (saved_ftrace_func != ftrace_trace_function) {
+ saved_ftrace_func = ftrace_trace_function;
+ command |= FTRACE_UPDATE_TRACE_FUNC;
+ }
+
+ if (!command || !ftrace_enabled)
+ goto out;
+
+ ftrace_run_update_code(command);
out:
mutex_unlock(&ftraced_lock);
}
static void notrace ftrace_shutdown(void)
{
+ int command = 0;
+
mutex_lock(&ftraced_lock);
ftraced_suspend--;
- if (ftraced_suspend)
+ if (!ftraced_suspend)
+ command |= FTRACE_DISABLE_CALLS;
+
+ if (saved_ftrace_func != ftrace_trace_function) {
+ saved_ftrace_func = ftrace_trace_function;
+ command |= FTRACE_UPDATE_TRACE_FUNC;
+ }
+
+ if (!command || !ftrace_enabled)
goto out;
- if (ftrace_enabled)
- ftrace_run_shutdown_code();
-
- __register_ftrace_function(&ftrace_shutdown_ops);
+ ftrace_run_update_code(command);
out:
mutex_unlock(&ftraced_lock);
}
static void notrace ftrace_startup_sysctl(void)
{
+ int command = FTRACE_ENABLE_MCOUNT;
+
mutex_lock(&ftraced_lock);
+ /* Force update next time */
+ saved_ftrace_func = NULL;
/* ftraced_suspend is true if we want ftrace running */
if (ftraced_suspend)
- ftrace_run_startup_code();
+ command |= FTRACE_ENABLE_CALLS;
+
+ ftrace_run_update_code(command);
mutex_unlock(&ftraced_lock);
}
static void notrace ftrace_shutdown_sysctl(void)
{
+ int command = FTRACE_DISABLE_MCOUNT;
+
mutex_lock(&ftraced_lock);
/* ftraced_suspend is true if ftrace is running */
if (ftraced_suspend)
- ftrace_run_shutdown_code();
+ command |= FTRACE_DISABLE_CALLS;
+
+ ftrace_run_update_code(command);
mutex_unlock(&ftraced_lock);
}
@@ -430,11 +456,13 @@
struct dyn_ftrace *p;
struct hlist_head head;
struct hlist_node *t;
+ int save_ftrace_enabled;
cycle_t start, stop;
int i;
- /* Don't be calling ftrace ops now */
- __unregister_ftrace_function(&ftrace_shutdown_ops);
+ /* Don't be recording funcs now */
+ save_ftrace_enabled = ftrace_enabled;
+ ftrace_enabled = 0;
start = now(raw_smp_processor_id());
ftrace_update_cnt = 0;
@@ -449,7 +477,7 @@
/* all CPUS are stopped, we are safe to modify code */
hlist_for_each_entry(p, t, &head, node) {
- ftrace_code_disable(p, MCOUNT_ADDR);
+ ftrace_code_disable(p);
ftrace_update_cnt++;
}
@@ -459,7 +487,7 @@
ftrace_update_time = stop - start;
ftrace_update_tot_cnt += ftrace_update_cnt;
- __register_ftrace_function(&ftrace_shutdown_ops);
+ ftrace_enabled = save_ftrace_enabled;
return 0;
}
@@ -515,11 +543,6 @@
struct ftrace_page *pg;
int cnt;
int i;
- int ret;
-
- ret = ftrace_dyn_arch_init();
- if (ret)
- return ret;
/* allocate a few pages */
ftrace_pages_start = (void *)get_zeroed_page(GFP_KERNEL);
@@ -557,11 +580,19 @@
return 0;
}
-static int __init notrace ftrace_shutdown_init(void)
+static int __init notrace ftrace_dynamic_init(void)
{
struct task_struct *p;
+ unsigned long addr;
int ret;
+ addr = (unsigned long)ftrace_record_ip;
+ stop_machine_run(ftrace_dyn_arch_init, &addr, NR_CPUS);
+
+ /* ftrace_dyn_arch_init places the return code in addr */
+ if (addr)
+ return addr;
+
ret = ftrace_dyn_table_alloc();
if (ret)
return ret;
@@ -570,12 +601,12 @@
if (IS_ERR(p))
return -1;
- __register_ftrace_function(&ftrace_shutdown_ops);
+ last_ftrace_enabled = ftrace_enabled = 1;
return 0;
}
-core_initcall(ftrace_shutdown_init);
+core_initcall(ftrace_dynamic_init);
#else
# define ftrace_startup() do { } while (0)
# define ftrace_shutdown() do { } while (0)
@@ -599,9 +630,8 @@
int ret;
mutex_lock(&ftrace_sysctl_lock);
- ftrace_startup();
-
ret = __register_ftrace_function(ops);
+ ftrace_startup();
mutex_unlock(&ftrace_sysctl_lock);
return ret;
@@ -619,10 +649,7 @@
mutex_lock(&ftrace_sysctl_lock);
ret = __unregister_ftrace_function(ops);
-
- if (ftrace_list == &ftrace_list_end)
- ftrace_shutdown();
-
+ ftrace_shutdown();
mutex_unlock(&ftrace_sysctl_lock);
return ret;