tracing/function-return-tracer: store return stack into task_struct and allocate it dynamically

Impact: use deeper function tracing depth safely

Some tests showed that function return tracing needed a more deeper depth
of function calls. But it could be unsafe to store these return addresses
to the stack.

So these arrays will now be allocated dynamically into task_struct of current
only when the tracer is activated.

Typical scheme when tracer is activated:
- allocate a return stack for each task in global list.
- fork: allocate the return stack for the newly created task
- exit: free return stack of current
- idle init: same as fork

I chose a default depth of 50. I don't have overruns anymore.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

9 files changed, 137 insertions, 58 deletions

diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index 2bb43b433e07..754a3e082f94 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -29,7 +29,6 @@ struct dyn_arch_ftrace {
 #endif /* CONFIG_FUNCTION_TRACER */
 
 #ifdef CONFIG_FUNCTION_RET_TRACER
-#define FTRACE_RET_STACK_SIZE 20
 
 #ifndef __ASSEMBLY__
 
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index e90e81ef6ab9..0921b4018c11 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -40,36 +40,8 @@ struct thread_info {
                                                 */
         __u8                    supervisor_stack[0];
 #endif
-
-#ifdef CONFIG_FUNCTION_RET_TRACER
-        /* Index of current stored adress in ret_stack */
-        int             curr_ret_stack;
-        /* Stack of return addresses for return function tracing */
-        struct ftrace_ret_stack ret_stack[FTRACE_RET_STACK_SIZE];
-        /*
-         * Number of functions that haven't been traced
-         * because of depth overrun.
-         */
-        atomic_t        trace_overrun;
-#endif
 };
 
-#ifdef CONFIG_FUNCTION_RET_TRACER
-#define INIT_THREAD_INFO(tsk)                   \
-{                                               \
-        .task           = &tsk,                 \
-        .exec_domain    = &default_exec_domain, \
-        .flags          = 0,                    \
-        .cpu            = 0,                    \
-        .preempt_count  = 1,                    \
-        .addr_limit     = KERNEL_DS,            \
-        .restart_block = {                      \
-                .fn = do_no_restart_syscall,    \
-        },                                      \
-        .curr_ret_stack = -1,\
-        .trace_overrun  = ATOMIC_INIT(0)        \
-}
-#else
 #define INIT_THREAD_INFO(tsk)                   \
 {                                               \
         .task           = &tsk,                 \
@@ -82,7 +54,6 @@ struct thread_info {
                 .fn = do_no_restart_syscall,    \
         },                                      \
 }
-#endif
 
 #define init_thread_info        (init_thread_union.thread_info)
 #define init_stack              (init_thread_union.stack)
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 356bb1eb6e9a..bb137f7297ed 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -350,19 +350,21 @@ static int push_return_trace(unsigned long ret, unsigned long long time,
                                 unsigned long func)
 {
         int index;
-        struct thread_info *ti = current_thread_info();
+
+        if (!current->ret_stack)
+                return -EBUSY;
 
         /* The return trace stack is full */
-        if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1) {
-                atomic_inc(&ti->trace_overrun);
+        if (current->curr_ret_stack == FTRACE_RETFUNC_DEPTH - 1) {
+                atomic_inc(&current->trace_overrun);
                 return -EBUSY;
         }
 
-        index = ++ti->curr_ret_stack;
+        index = ++current->curr_ret_stack;
         barrier();
-        ti->ret_stack[index].ret = ret;
-        ti->ret_stack[index].func = func;
-        ti->ret_stack[index].calltime = time;
+        current->ret_stack[index].ret = ret;
+        current->ret_stack[index].func = func;
+        current->ret_stack[index].calltime = time;
 
         return 0;
 }
@@ -373,13 +375,12 @@ static void pop_return_trace(unsigned long *ret, unsigned long long *time,
 {
         int index;
 
-        struct thread_info *ti = current_thread_info();
-        index = ti->curr_ret_stack;
-        *ret = ti->ret_stack[index].ret;
-        *func = ti->ret_stack[index].func;
-        *time = ti->ret_stack[index].calltime;
-        *overrun = atomic_read(&ti->trace_overrun);
-        ti->curr_ret_stack--;
+        index = current->curr_ret_stack;
+        *ret = current->ret_stack[index].ret;
+        *func = current->ret_stack[index].func;
+        *time = current->ret_stack[index].calltime;
+        *overrun = atomic_read(&current->trace_overrun);
+        current->curr_ret_stack--;
 }
 
 /*
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index f7ba4ea5e128..2ba259b2defa 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -323,6 +323,8 @@ struct ftrace_retfunc {
 };
 
 #ifdef CONFIG_FUNCTION_RET_TRACER
+#define FTRACE_RETFUNC_DEPTH 50
+#define FTRACE_RETSTACK_ALLOC_SIZE 32
 /* Type of a callback handler of tracing return function */
 typedef void (*trace_function_return_t)(struct ftrace_retfunc *);
 
@@ -330,6 +332,9 @@ extern int register_ftrace_return(trace_function_return_t func);
 /* The current handler in use */
 extern trace_function_return_t ftrace_function_return;
 extern void unregister_ftrace_return(void);
+
+extern void ftrace_retfunc_init_task(struct task_struct *t);
+extern void ftrace_retfunc_exit_task(struct task_struct *t);
 #endif
 
 #endif /* _LINUX_FTRACE_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index c8e0db464206..bee1e93c95ad 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1352,6 +1352,17 @@ struct task_struct {
         unsigned long default_timer_slack_ns;
 
         struct list_head        *scm_work_list;
+#ifdef CONFIG_FUNCTION_RET_TRACER
+        /* Index of current stored adress in ret_stack */
+        int curr_ret_stack;
+        /* Stack of return addresses for return function tracing */
+        struct ftrace_ret_stack *ret_stack;
+        /*
+         * Number of functions that haven't been traced
+         * because of depth overrun.
+         */
+        atomic_t trace_overrun;
+#endif
 };
 
 /*
@@ -2006,18 +2017,6 @@ static inline void setup_thread_stack(struct task_struct *p, struct task_struct
 {
         *task_thread_info(p) = *task_thread_info(org);
         task_thread_info(p)->task = p;
-
-#ifdef CONFIG_FUNCTION_RET_TRACER
-        /*
-         * When fork() creates a child process, this function is called.
-         * But the child task may not inherit the return adresses traced
-         * by the return function tracer because it will directly execute
-         * in userspace and will not return to kernel functions its parent
-         * used.
-         */
-        task_thread_info(p)->curr_ret_stack = -1;
-        atomic_set(&task_thread_info(p)->trace_overrun, 0);
-#endif
 }
 
 static inline unsigned long *end_of_stack(struct task_struct *p)
diff --git a/kernel/exit.c b/kernel/exit.c
index 35c8ec2ba03a..b9d446329da1 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -47,6 +47,7 @@
 #include <linux/task_io_accounting_ops.h>
 #include <linux/tracehook.h>
 #include <trace/sched.h>
+#include <linux/ftrace.h>
 
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
@@ -1127,7 +1128,9 @@ NORET_TYPE void do_exit(long code)
         preempt_disable();
         /* causes final put_task_struct in finish_task_switch(). */
         tsk->state = TASK_DEAD;
-
+#ifdef CONFIG_FUNCTION_RET_TRACER
+        ftrace_retfunc_exit_task(tsk);
+#endif
         schedule();
         BUG();
         /* Avoid "noreturn function does return".  */
diff --git a/kernel/fork.c b/kernel/fork.c
index ac62f43ee430..d1eb30e69ccc 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -47,6 +47,7 @@
 #include <linux/mount.h>
 #include <linux/audit.h>
 #include <linux/memcontrol.h>
+#include <linux/ftrace.h>
 #include <linux/profile.h>
 #include <linux/rmap.h>
 #include <linux/acct.h>
@@ -1269,6 +1270,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         total_forks++;
         spin_unlock(&current->sighand->siglock);
         write_unlock_irq(&tasklist_lock);
+#ifdef CONFIG_FUNCTION_RET_TRACER
+        ftrace_retfunc_init_task(p);
+#endif
         proc_fork_connector(p);
         cgroup_post_fork(p);
         return p;
diff --git a/kernel/sched.c b/kernel/sched.c
index 4de56108c86f..fb17205950de 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5901,6 +5901,9 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
          * The idle tasks have their own, simple scheduling class:
          */
         idle->sched_class = &idle_sched_class;
+#ifdef CONFIG_FUNCTION_RET_TRACER
+        ftrace_retfunc_init_task(idle);
+#endif
 }
 
 /*
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f212da486689..90d99fb02ae4 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1498,10 +1498,77 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
 
 #ifdef CONFIG_FUNCTION_RET_TRACER
 
+static atomic_t ftrace_retfunc_active;
+
 /* The callback that hooks the return of a function */
 trace_function_return_t ftrace_function_return =
                         (trace_function_return_t)ftrace_stub;
 
+
+/* Try to assign a return stack array on FTRACE_RETSTACK_ALLOC_SIZE tasks. */
+static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
+{
+        int i;
+        int ret = 0;
+        unsigned long flags;
+        int start = 0, end = FTRACE_RETSTACK_ALLOC_SIZE;
+        struct task_struct *g, *t;
+
+        for (i = 0; i < FTRACE_RETSTACK_ALLOC_SIZE; i++) {
+                ret_stack_list[i] = kmalloc(FTRACE_RETFUNC_DEPTH
+                                        * sizeof(struct ftrace_ret_stack),
+                                        GFP_KERNEL);
+                if (!ret_stack_list[i]) {
+                        start = 0;
+                        end = i;
+                        ret = -ENOMEM;
+                        goto free;
+                }
+        }
+
+        read_lock_irqsave(&tasklist_lock, flags);
+        do_each_thread(g, t) {
+                if (start == end) {
+                        ret = -EAGAIN;
+                        goto unlock;
+                }
+
+                if (t->ret_stack == NULL) {
+                        t->ret_stack = ret_stack_list[start++];
+                        t->curr_ret_stack = -1;
+                        atomic_set(&t->trace_overrun, 0);
+                }
+        } while_each_thread(g, t);
+
+unlock:
+        read_unlock_irqrestore(&tasklist_lock, flags);
+free:
+        for (i = start; i < end; i++)
+                kfree(ret_stack_list[i]);
+        return ret;
+}
+
+/* Allocate a return stack for each task */
+static int start_return_tracing(void)
+{
+        struct ftrace_ret_stack **ret_stack_list;
+        int ret;
+
+        ret_stack_list = kmalloc(FTRACE_RETSTACK_ALLOC_SIZE *
+                                sizeof(struct ftrace_ret_stack *),
+                                GFP_KERNEL);
+
+        if (!ret_stack_list)
+                return -ENOMEM;
+
+        do {
+                ret = alloc_retstack_tasklist(ret_stack_list);
+        } while (ret == -EAGAIN);
+
+        kfree(ret_stack_list);
+        return ret;
+}
+
 int register_ftrace_return(trace_function_return_t func)
 {
         int ret = 0;
@@ -1516,7 +1583,12 @@ int register_ftrace_return(trace_function_return_t func)
                 ret = -EBUSY;
                 goto out;
         }
-
+        atomic_inc(&ftrace_retfunc_active);
+        ret = start_return_tracing();
+        if (ret) {
+                atomic_dec(&ftrace_retfunc_active);
+                goto out;
+        }
         ftrace_tracing_type = FTRACE_TYPE_RETURN;
         ftrace_function_return = func;
         ftrace_startup();
@@ -1530,6 +1602,7 @@ void unregister_ftrace_return(void)
 {
         mutex_lock(&ftrace_sysctl_lock);
 
+        atomic_dec(&ftrace_retfunc_active);
         ftrace_function_return = (trace_function_return_t)ftrace_stub;
         ftrace_shutdown();
         /* Restore normal tracing type */
@@ -1537,6 +1610,27 @@ void unregister_ftrace_return(void)
 
         mutex_unlock(&ftrace_sysctl_lock);
 }
+
+/* Allocate a return stack for newly created task */
+void ftrace_retfunc_init_task(struct task_struct *t)
+{
+        if (atomic_read(&ftrace_retfunc_active)) {
+                t->ret_stack = kmalloc(FTRACE_RETFUNC_DEPTH
+                                * sizeof(struct ftrace_ret_stack),
+                                GFP_KERNEL);
+                if (!t->ret_stack)
+                        return;
+                t->curr_ret_stack = -1;
+                atomic_set(&t->trace_overrun, 0);
+        } else
+                t->ret_stack = NULL;
+}
+
+void ftrace_retfunc_exit_task(struct task_struct *t)
+{
+        kfree(t->ret_stack);
+        t->ret_stack = NULL;
+}
 #endif