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Subject[RFC PATCH 4/12 v2] ptrace: introduce the empty "struct ptrace_context"
Suggested by Roland.

Introduce the new "struct ptrace_context" and add the pointer to task_struct.
The next patches will move all ptrace-related fields from task_struct into
this struct. From now, if the task was ever ptraced it has ->ptrace_ctx
!= NULL. Freed by free_task() along with task_struct itself.

With utrace based ptrace we can move this struct into utrace_engine->data.

include/linux/sched.h | 1 +
include/linux/ptrace.h | 4 ++++
include/linux/tracehook.h | 34 ++++++++++++++++++++++++++++++++++
kernel/fork.c | 5 +++++
kernel/ptrace.c | 36 +++++++++++++++++++++++++++++++++++-
5 files changed, 79 insertions(+), 1 deletion(-)

--- PTRACE/include/linux/sched.h~3_STRUCT 2009-05-28 06:26:19.000000000 +0200
+++ PTRACE/include/linux/sched.h 2009-05-28 07:26:35.000000000 +0200
@@ -1201,6 +1201,7 @@ struct task_struct {
struct list_head sibling; /* linkage in my parent's children list */
struct task_struct *group_leader; /* threadgroup leader */

+ struct ptrace_context *ptrace_ctx;
/*
* ptraced is the list of tasks this task is using ptrace on.
* This includes both natural children and PTRACE_ATTACH targets.
--- PTRACE/include/linux/ptrace.h~3_STRUCT 2009-05-28 06:26:19.000000000 +0200
+++ PTRACE/include/linux/ptrace.h 2009-05-28 07:26:35.000000000 +0200
@@ -79,6 +79,10 @@
#include <linux/compiler.h> /* For unlikely. */
#include <linux/sched.h> /* For struct task_struct. */

+struct ptrace_context {
+};
+
+extern int alloc_ptrace_context(struct task_struct *child);

extern long arch_ptrace(struct task_struct *child, long request, long addr, long data);
extern int ptrace_traceme(void);
--- PTRACE/include/linux/tracehook.h~3_STRUCT 2009-05-28 06:26:19.000000000 +0200
+++ PTRACE/include/linux/tracehook.h 2009-05-28 07:39:21.000000000 +0200
@@ -243,6 +243,40 @@ static inline int tracehook_prepare_clon
}

/**
+ * tracehook_init_task - initialize the new task
+ * @task: the task to initialize
+ * @clone_flags: %CLONE_* flags from clone/fork/vfork system call
+ * @trace: return value from tracehook_prepare_clone()
+ *
+ * This is called immediately after dup_task_struct().
+ * It must clear/reset any tracing state so that tracehook_free_task()
+ * will work safely if the task creation fails. If the task creation
+ * succeeds, a tracehook_finish_clone() call will follow with locks
+ * held, before @task starts or is accessible to anyone else.
+ *
+ * Called with no locks held.
+ */
+static inline int tracehook_init_task(struct task_struct *task,
+ unsigned long clone_flags, int trace)
+{
+ task->ptrace_ctx = NULL;
+ if (unlikely((clone_flags & CLONE_PTRACE) || trace))
+ return alloc_ptrace_context(task);
+ return 0;
+}
+
+/**
+ * tracehook_free_task - task is about to be freed
+ * @task: task that will be freed
+ *
+ * May be called from any context.
+ */
+static inline void tracehook_free_task(struct task_struct *task)
+{
+ kfree(task->ptrace_ctx);
+}
+
+/**
* tracehook_finish_clone - new child created and being attached
* @child: new child task
* @clone_flags: %CLONE_* flags from clone/fork/vfork system call
--- PTRACE/kernel/fork.c~3_STRUCT 2009-05-28 06:26:19.000000000 +0200
+++ PTRACE/kernel/fork.c 2009-05-28 07:26:35.000000000 +0200
@@ -143,6 +143,7 @@ void free_task(struct task_struct *tsk)
free_thread_info(tsk->stack);
rt_mutex_debug_task_free(tsk);
ftrace_graph_exit_task(tsk);
+ tracehook_free_task(tsk);
free_task_struct(tsk);
}
EXPORT_SYMBOL(free_task);
@@ -982,6 +983,10 @@ static struct task_struct *copy_process(
if (!p)
goto fork_out;

+ retval = tracehook_init_task(p, clone_flags, trace);
+ if (retval)
+ goto bad_fork_free;
+
rt_mutex_init_task(p);

#ifdef CONFIG_PROVE_LOCKING
--- PTRACE/kernel/ptrace.c~3_STRUCT 2009-05-28 06:26:19.000000000 +0200
+++ PTRACE/kernel/ptrace.c 2009-05-28 08:09:47.000000000 +0200
@@ -174,6 +174,32 @@ bool ptrace_may_access(struct task_struc
return !err;
}

+/*
+ * Check the task has ->ptrace_ctx or alloc the new one. Called
+ * from preemptible context when we are going to attach to this task.
+ * Once allocated, ->ptrace_ctx is never freed until free_task().
+ */
+int alloc_ptrace_context(struct task_struct *tsk)
+{
+ struct ptrace_context *ptrace_ctx;
+
+ if (tsk->ptrace_ctx)
+ return 0;
+
+ ptrace_ctx = kzalloc(sizeof(*ptrace_ctx), GFP_KERNEL);
+ if (unlikely(!ptrace_ctx))
+ return -ENOMEM;
+
+ task_lock(tsk);
+ if (likely(!tsk->ptrace_ctx))
+ tsk->ptrace_ctx = ptrace_ctx;
+ else
+ kfree(ptrace_ctx);
+ task_unlock(tsk);
+
+ return 0;
+}
+
int ptrace_attach(struct task_struct *task)
{
int retval;
@@ -199,6 +225,10 @@ int ptrace_attach(struct task_struct *ta
if (retval)
goto unlock_creds;

+ retval = alloc_ptrace_context(task);
+ if (unlikely(retval))
+ goto unlock_creds;
+
write_lock_irq(&tasklist_lock);
retval = -EPERM;
if (unlikely(task->exit_state))
@@ -230,8 +260,12 @@ out:
*/
int ptrace_traceme(void)
{
- int ret = -EPERM;
+ int ret = alloc_ptrace_context(current);

+ if (unlikely(ret))
+ return ret;
+
+ ret = -EPERM;
write_lock_irq(&tasklist_lock);
/* Are we already being traced? */
if (!task_ptrace(current)) {


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