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>

5 files changed, 261 insertions, 84 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index f47b9b5440d2..e6517ce0b824 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1110,10 +1110,50 @@ ENDPROC(xen_failsafe_callback)
 #endif  /* CONFIG_XEN */
 
 #ifdef CONFIG_FTRACE
+#ifdef CONFIG_DYNAMIC_FTRACE
+
+ENTRY(mcount)
+        pushl %eax
+        pushl %ecx
+        pushl %edx
+        movl 0xc(%esp), %eax
+
+.globl mcount_call
+mcount_call:
+        call ftrace_stub
+
+        popl %edx
+        popl %ecx
+        popl %eax
+
+        ret
+END(mcount)
+
+ENTRY(ftrace_caller)
+        pushl %eax
+        pushl %ecx
+        pushl %edx
+        movl 0xc(%esp), %eax
+        movl 0x4(%ebp), %edx
+
+.globl ftrace_call
+ftrace_call:
+        call ftrace_stub
+
+        popl %edx
+        popl %ecx
+        popl %eax
+
+.globl ftrace_stub
+ftrace_stub:
+        ret
+END(ftrace_caller)
+
+#else /* ! CONFIG_DYNAMIC_FTRACE */
+
 ENTRY(mcount)
         cmpl $ftrace_stub, ftrace_trace_function
         jnz trace
-
 .globl ftrace_stub
 ftrace_stub:
         ret
@@ -1126,7 +1166,7 @@ trace:
         movl 0xc(%esp), %eax
         movl 0x4(%ebp), %edx
 
-        call   *ftrace_trace_function
+        call *ftrace_trace_function
 
         popl %edx
         popl %ecx
@@ -1134,7 +1174,8 @@ trace:
 
         jmp ftrace_stub
 END(mcount)
-#endif
+#endif /* CONFIG_DYNAMIC_FTRACE */
+#endif /* CONFIG_FTRACE */
 
 .section .rodata,"a"
 #include "syscall_table_32.S"
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index f046e0c64883..fe25e5febca3 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -55,6 +55,70 @@
         .code64
 
 #ifdef CONFIG_FTRACE
+#ifdef CONFIG_DYNAMIC_FTRACE
+ENTRY(mcount)
+
+        subq $0x38, %rsp
+        movq %rax, (%rsp)
+        movq %rcx, 8(%rsp)
+        movq %rdx, 16(%rsp)
+        movq %rsi, 24(%rsp)
+        movq %rdi, 32(%rsp)
+        movq %r8, 40(%rsp)
+        movq %r9, 48(%rsp)
+
+        movq 0x38(%rsp), %rdi
+
+.globl mcount_call
+mcount_call:
+        call ftrace_stub
+
+        movq 48(%rsp), %r9
+        movq 40(%rsp), %r8
+        movq 32(%rsp), %rdi
+        movq 24(%rsp), %rsi
+        movq 16(%rsp), %rdx
+        movq 8(%rsp), %rcx
+        movq (%rsp), %rax
+        addq $0x38, %rsp
+
+        retq
+END(mcount)
+
+ENTRY(ftrace_caller)
+
+        /* taken from glibc */
+        subq $0x38, %rsp
+        movq %rax, (%rsp)
+        movq %rcx, 8(%rsp)
+        movq %rdx, 16(%rsp)
+        movq %rsi, 24(%rsp)
+        movq %rdi, 32(%rsp)
+        movq %r8, 40(%rsp)
+        movq %r9, 48(%rsp)
+
+        movq 0x38(%rsp), %rdi
+        movq 8(%rbp), %rsi
+
+.globl ftrace_call
+ftrace_call:
+        call ftrace_stub
+
+        movq 48(%rsp), %r9
+        movq 40(%rsp), %r8
+        movq 32(%rsp), %rdi
+        movq 24(%rsp), %rsi
+        movq 16(%rsp), %rdx
+        movq 8(%rsp), %rcx
+        movq (%rsp), %rax
+        addq $0x38, %rsp
+
+.globl ftrace_stub
+ftrace_stub:
+        retq
+END(ftrace_caller)
+
+#else /* ! CONFIG_DYNAMIC_FTRACE */
 ENTRY(mcount)
         cmpq $ftrace_stub, ftrace_trace_function
         jnz trace
@@ -89,7 +153,8 @@ trace:
 
         jmp ftrace_stub
 END(mcount)
-#endif
+#endif /* CONFIG_DYNAMIC_FTRACE */
+#endif /* CONFIG_FTRACE */
 
 #ifndef CONFIG_PREEMPT
 #define retint_kernel retint_restore_args
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index b69795efa226..9f44623e0072 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -109,10 +109,49 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
         return faulted;
 }
 
-int __init ftrace_dyn_arch_init(void)
+notrace int ftrace_update_ftrace_func(ftrace_func_t func)
+{
+        unsigned long ip = (unsigned long)(&ftrace_call);
+        unsigned char old[5], *new;
+        int ret;
+
+        ip += CALL_BACK;
+
+        memcpy(old, &ftrace_call, 5);
+        new = ftrace_call_replace(ip, (unsigned long)func);
+        ret = ftrace_modify_code(ip, old, new);
+
+        return ret;
+}
+
+notrace int ftrace_mcount_set(unsigned long *data)
+{
+        unsigned long ip = (long)(&mcount_call);
+        unsigned long *addr = data;
+        unsigned char old[5], *new;
+
+        /* ip is at the location, but modify code will subtact this */
+        ip += CALL_BACK;
+
+        /*
+         * Replace the mcount stub with a pointer to the
+         * ip recorder function.
+         */
+        memcpy(old, &mcount_call, 5);
+        new = ftrace_call_replace(ip, *addr);
+        *addr = ftrace_modify_code(ip, old, new);
+
+        return 0;
+}
+
+int __init ftrace_dyn_arch_init(void *data)
 {
         const unsigned char *const *noptable = find_nop_table();
 
+        /* This is running in kstop_machine */
+
+        ftrace_mcount_set(data);
+
         ftrace_nop = (unsigned long *)noptable[CALL_BACK];
 
         return 0;
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index d509ad6c9cb8..b0dd0093058f 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -56,9 +56,14 @@ struct dyn_ftrace {
 extern int ftrace_ip_converted(unsigned long ip);
 extern unsigned char *ftrace_nop_replace(void);
 extern unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr);
-extern int ftrace_dyn_arch_init(void);
+extern int ftrace_dyn_arch_init(void *data);
+extern int ftrace_mcount_set(unsigned long *data);
 extern int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
                               unsigned char *new_code);
+extern int ftrace_update_ftrace_func(ftrace_func_t func);
+extern void ftrace_caller(void);
+extern void ftrace_call(void);
+extern void mcount_call(void);
 #endif
 
 #ifdef CONFIG_FRAME_POINTER
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f6d9af3bf66b..88544f9bc0ed 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 @@ static int notrace __unregister_ftrace_function(struct ftrace_ops *ops)
 
 #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 @@ ftrace_add_hash(struct dyn_ftrace *node, unsigned long key)
         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 notrace struct dyn_ftrace *ftrace_alloc_shutdown_node(unsigned long ip)
 }
 
 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 @@ ftrace_record_ip(unsigned long ip, unsigned long parent_ip)
         int resched;
         int atomic;
 
+        if (!ftrace_enabled)
+                return;
+
         resched = need_resched();
         preempt_disable_notrace();
 
@@ -251,11 +252,12 @@ ftrace_record_ip(unsigned long ip, unsigned long parent_ip)
 
         /*
          * 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 @@ ftrace_record_ip(unsigned long ip, unsigned long parent_ip)
                 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 @@ static void notrace ftrace_replace_code(int saved)
                         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 void notrace ftrace_replace_code(int saved)
         }
 }
 
-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 @@ static notrace void ftrace_shutdown_replenish(void)
         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 @@ ftrace_code_disable(struct dyn_ftrace *rec, unsigned long addr)
         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)
+        if (ftraced_suspend == 1)
+                command |= FTRACE_ENABLE_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;
-        __unregister_ftrace_function(&ftrace_shutdown_ops);
 
-        if (ftrace_enabled)
-                ftrace_run_startup_code();
+        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)
-                goto out;
+        if (!ftraced_suspend)
+                command |= FTRACE_DISABLE_CALLS;
 
-        if (ftrace_enabled)
-                ftrace_run_shutdown_code();
+        if (saved_ftrace_func != ftrace_trace_function) {
+                saved_ftrace_func = ftrace_trace_function;
+                command |= FTRACE_UPDATE_TRACE_FUNC;
+        }
 
-        __register_ftrace_function(&ftrace_shutdown_ops);
+        if (!command || !ftrace_enabled)
+                goto out;
+
+        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 @@ static int notrace __ftrace_update_code(void *ignore)
         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 @@ static int notrace __ftrace_update_code(void *ignore)
 
                 /* 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 @@ static int notrace __ftrace_update_code(void *ignore)
         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 @@ static int __init ftrace_dyn_table_alloc(void)
         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 @@ static int __init ftrace_dyn_table_alloc(void)
         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 @@ static int __init notrace ftrace_shutdown_init(void)
         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 register_ftrace_function(struct ftrace_ops *ops)
         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 @@ int unregister_ftrace_function(struct ftrace_ops *ops)
 
         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;