WebSVN – HelenOS – Diff – //branches/tracing/kernel/generic/src/udebug/udebug_ipc.c

 #include <syscall/copy.h>
 #include <udebug/udebug.h>
 #include <udebug/udebug_ipc.h>
 /**
- * Get and lock a phone's callee task.
+ * Get a phone's callee task id.
+ *
- * This will return a pointer to the task to which the phone
+ * This will return the id of the task to which the phone
- * is connected. It will lock the task, making sure it exists.
+ * is connected.
+ *
  * Interrupts must be already disabled.
- *
- * (TODO: make sure the udebug-cleanup of the task hasn't
- * started yet)
  */
-static task_t *get_lock_callee_task(phone_t *phone)
+static task_id_t get_callee_task_id(phone_t *phone)
+{
     answerbox_t *box;
-    task_t *ta;
     task_id_t taskid;
     spinlock_lock(&phone->lock);
     if (phone->state != IPC_PHONE_CONNECTED) {
         spinlock_unlock(&phone->lock);
+    }
     box = phone->callee;
     spinlock_lock(&box->lock);
-    ta = box->task;
-    taskid = ta->taskid;
+    taskid = box->task->taskid;
     spinlock_unlock(&box->lock);
     spinlock_unlock(&phone->lock);
+    return taskid;
+}
+/**
-    /* Locking decoupled using taskid */
+ * Get and lock a phone's callee task.
+ *
+ * This will return a pointer to the task to which the phone
+ * is connected. It will lock the task, making sure it exists.
+ *
+ * Interrupts must be already disabled.
+ *
+ * (TODO: make sure the udebug-cleanup of the task hasn't
+ * started yet)
+ */
+static task_t *get_lock_callee_task(phone_t *phone)
+{
+    task_t *ta;
+    task_id_t taskid;
+    taskid = get_callee_task_id(phone);
     spinlock_lock(&tasks_lock);
     ta = task_find_by_id(taskid);
     if (ta == NULL) {
         spinlock_unlock(&tasks_lock);
         return NULL;
     spinlock_unlock(&tasks_lock);
     return ta;
+}
 /**
- * Verify that thread t is valid for debugging ops.
+ * Prepare a thread for a debugging operation.
+ *
- * Verifies that t belongs to task ta and that debugging operations
+ * Simply put, return thread t with t->debug_lock held,
- * may be used on it.
+ * but only if it verifies all conditions.
+ *
+ * Specifically, verifies that thread t exists, is a userspace thread,
+ * belongs to the callee of 'phone'. It also locks t->debug_lock,
+ * making sure that t->debug_active is true - that the thread is
+ * in a valid debugging session.
+ *
+ * Returns EOK if all went well, or an error code otherwise.
- * Thread t's lock must already be held and interrupts must be disabled.
+ * Interrupts must be already disabled when calling this function.
+ *
+ * Note: This function sports complicated locking.
  */
-static int verify_thread(thread_t *t, task_t *ta)
+static int _thread_op_begin(phone_t *phone, thread_t *t)
+{
+    int rc;
+    task_id_t taskid;
+    int task_match;
+    DEADLOCK_PROBE_INIT(p_tasklock);
+    taskid = get_callee_task_id(phone);
-    /* Verify that 't' exists and belongs to task 'ta' */
+    /* Need to lock down the thread and than it's owner task */
+grab_locks:
+    spinlock_lock(&threads_lock);
-    if (!thread_exists(t) || (t->task != ta)) {
+    if (!thread_exists(t)) {
+        spinlock_unlock(&threads_lock);
         return ENOENT;
+    }
+    spinlock_lock(&t->debug_lock);
+    spinlock_lock(&t->lock);
+    if (!spinlock_trylock(&t->task->lock)) {
+        spinlock_unlock(&t->lock);
+        spinlock_unlock(&t->debug_lock);
+        DEADLOCK_PROBE(p_tasklock, DEADLOCK_THRESHOLD);
+        goto grab_locks;    /* avoid deadlock */
+    }
+    /* Now verify that it's the callee */
+    task_match = (t->task->taskid == taskid);
+    spinlock_unlock(&t->task->lock);
+    if (!task_match) {
+        /* No such thread belonging to callee */
+        rc = ENOENT;
+        goto error_exit;
+    }
     /* Verify that 't' is a userspace thread */
     if ((t->flags & THREAD_FLAG_USPACE) == 0) {
         /* It's not, deny its existence */
-        return ENOENT;
+        rc = ENOENT;
+        goto error_exit;
+    }
     if ((t->debug_active != true) || (t->debug_stop != true)) {
         /* Not in debugging session or already has GO */
-        return EBUSY;
+        rc = ENOENT;
+        goto error_exit;
+    }
+    spinlock_unlock(&threads_lock);
+    spinlock_unlock(&t->lock);
+    /* Only t->debug_lock left */
+    return EOK; /* All went well */
+    /* Executed when a check on the thread fails */
-    return EOK;
+error_exit:
+    spinlock_unlock(&t->lock);
+    spinlock_unlock(&t->debug_lock);
+    spinlock_unlock(&threads_lock);
+    /* No locks left here */
+    return rc;  /* Some errors occured */
+}
+static void _thread_op_end(thread_t *t)
+{
+    spinlock_unlock(&t->debug_lock);
+}
 static int udebug_rp_begin(call_t *call, phone_t *phone)
+{
     task_t *ta;
 static int udebug_rp_go(call_t *call, phone_t *phone)
+{
     thread_t *t;
-    task_t *ta;
     ipl_t ipl;
     int rc;
     klog_printf("debug_go()");
-    ipl = interrupts_disable();
+    t = (thread_t *)IPC_GET_ARG2(call->data);
-    ta = get_lock_callee_task(phone);
-    spinlock_unlock(&ta->lock);
-    // TODO: don't lock ta
-    t = (thread_t *) IPC_GET_ARG2(call->data);
-    spinlock_lock(&threads_lock);
-    if (!thread_exists(t)) {
-        spinlock_unlock(&threads_lock);
-        interrupts_restore(ipl);
+    ipl = interrupts_disable();
-        return ENOENT;
-    }
-    spinlock_lock(&t->debug_lock);
-    /* Verify that thread t may be operated on */
+    /* On success, this will lock t->debug_lock */
-    rc = verify_thread(t, ta);
+    rc = _thread_op_begin(phone, t);
     if (rc != EOK) {
-        spinlock_unlock(&t->debug_lock);
-        spinlock_unlock(&threads_lock);
         interrupts_restore(ipl);
         return rc;
+    }
-    /*
-     * Since t->debug_active == true and t->debug_lock is held,
-     * we can safely release threads_lock and t will continue
-     * to exist (and will stay in debug_active state)
-     */
-    spinlock_unlock(&threads_lock);
     t->debug_go_call = call;
     t->debug_stop = false;
     /*
      * Neither t's lock nor threads_lock may be held during wakeup
      */
     waitq_wakeup(&t->go_wq, WAKEUP_FIRST);
-    spinlock_unlock(&t->debug_lock);
+    _thread_op_end(t);
     interrupts_restore(ipl);
     return 0; /* no backsend */
+}
 static int udebug_rp_args_read(call_t *call, phone_t *phone)
+{
     thread_t *t;
-    task_t *ta;
     void *uspace_buffer;
     int rc;
     ipl_t ipl;
     unative_t buffer[6];
     klog_printf("debug_args_read()");
-    ipl = interrupts_disable();
-    ta = get_lock_callee_task(phone);
-    klog_printf("task %llu", ta->taskid);
-    spinlock_unlock(&ta->lock);
-    t = (thread_t *) IPC_GET_ARG2(call->data);
+    t = (thread_t *)IPC_GET_ARG2(call->data);
-    spinlock_lock(&threads_lock);
-    if (!thread_exists(t)) {
-        spinlock_unlock(&threads_lock);
-        interrupts_restore(ipl);
-        return ENOENT;
-    }
-    spinlock_lock(&t->debug_lock);
+    ipl = interrupts_disable();
-    /* Verify that thread t may be operated on */
+    /* On success, this will lock t->debug_lock */
-    rc = verify_thread(t, ta);
+    rc = _thread_op_begin(phone, t);
     if (rc != EOK) {
-        spinlock_unlock(&t->debug_lock);
-        spinlock_unlock(&threads_lock);
         interrupts_restore(ipl);
         return rc;
+    }
-    /*
-     * We can now safely release threads_lock as debug_active == true
-     * and t->debug_lock is held.
-     */
-    spinlock_unlock(&threads_lock);
     //FIXME: additionally we need to verify that we are inside a syscall
     /* Copy to a local buffer before releasing the lock */
     memcpy(buffer, t->syscall_args, 6 * sizeof(unative_t));
-    spinlock_unlock(&t->debug_lock);
+    _thread_op_end(t);
     interrupts_restore(ipl);
     /* Now copy to userspace */
     uspace_buffer = (void *)IPC_GET_ARG3(call->data);
     rc = copy_to_uspace(uspace_buffer, buffer, 6 * sizeof(unative_t));
     if (rc != 0) {
-        spinlock_unlock(&ta->lock);
         klog_printf("debug_args_read() - copy failed");
         return rc;
+    }
     klog_printf("debug_args_read() done");
+}
 static int udebug_rp_regs_read(call_t *call, phone_t *phone)
+{
     thread_t *t;
-    task_t *ta;
     void *uspace_buffer;
     unative_t to_copy;
     int rc;
     istate_t *state;
     istate_t state_copy;
     ipl_t ipl;
     klog_printf("debug_regs_read()");
-    ta = get_lock_callee_task(phone);
-    spinlock_unlock(&ta->lock);
-    //FIXME: don't lock ta
-    ipl = interrupts_disable();
-    spinlock_lock(&threads_lock);
     t = (thread_t *) IPC_GET_ARG2(call->data);
-    if (!thread_exists(t)) {
-        spinlock_unlock(&threads_lock);
-        interrupts_restore(ipl);
+    ipl = interrupts_disable();
-        return ENOENT;
-    }
-    spinlock_lock(&t->debug_lock);
-    /* Verify that thread t may be operated on */
+    /* On success, this will lock t->debug_lock */
-    rc = verify_thread(t, ta);
+    rc = _thread_op_begin(phone, t);
     if (rc != EOK) {
-        spinlock_unlock(&t->debug_lock);
-        spinlock_unlock(&threads_lock);
         interrupts_restore(ipl);
         return rc;
+    }
-    /*
-     * We can now safely release threads_lock as debug_active == true
-     * and t->debug_lock is held.
-     */
-    spinlock_unlock(&threads_lock);
     state = t->uspace_state;
     if (state == NULL) {
-        spinlock_unlock(&threads_lock);
+        _thread_op_end(t);
         interrupts_restore(ipl);
         klog_printf("debug_regs_read() - istate not available");
         return EBUSY;
+    }
     /* Copy to a local buffer so that we can release the lock */
     memcpy(&state_copy, state, sizeof(state_copy));
-    spinlock_unlock(&t->debug_lock);
+    _thread_op_end(t);
     interrupts_restore(ipl);
     uspace_buffer = (void *)IPC_GET_ARG3(call->data);
     to_copy = IPC_GET_ARG4(call->data);
     if (to_copy > sizeof(istate_t)) to_copy = sizeof(istate_t);
     klog_printf("debug_regs_read() done");
     return 1; /* actually need becksend with retval 0 */
+}
 static int udebug_rp_regs_write(call_t *call, phone_t *phone)
+{
     thread_t *t;
-    task_t *ta;
     void *uspace_data;
     unative_t to_copy;
     int rc;
     istate_t *state;
     istate_t data_copy;
     if (rc != 0) {
         klog_printf("debug_regs_write() - copy failed");
         return rc;
+    }
-    ta = get_lock_callee_task(phone);
-    spinlock_unlock(&ta->lock);
-    //FIXME: don't lock ta
     /* Now try to change the thread's uspace_state */
     ipl = interrupts_disable();
-    spinlock_lock(&threads_lock);
     t = (thread_t *) IPC_GET_ARG2(call->data);
-    if (!thread_exists(t)) {
-        spinlock_unlock(&threads_lock);
-        interrupts_restore(ipl);
-        return ENOENT;
-    }
-    spinlock_lock(&t->debug_lock);
+    /* On success, this will lock t->debug_lock */
-    /* Verify that thread t may be operated on */
-    rc = verify_thread(t, ta);
+    rc = _thread_op_begin(phone, t);
     if (rc != EOK) {
-        spinlock_unlock(&t->debug_lock);
-        spinlock_unlock(&threads_lock);
         interrupts_restore(ipl);
         return rc;
+    }
     state = t->uspace_state;
     if (state == NULL) {
-        spinlock_unlock(&t->debug_lock);
+        _thread_op_end(t);
         interrupts_restore(ipl);
         klog_printf("debug_regs_write() - istate not available");
         return EBUSY;
+    }
     memcpy(t->uspace_state, &data_copy, sizeof(t->uspace_state));
-    spinlock_unlock(&t->debug_lock);
+    _thread_op_end(t);
     interrupts_restore(ipl);
     /* Set answer values */
     IPC_SET_ARG1(call->data, to_copy);

Subversion Repositories HelenOS

(root)//branches/tracing/kernel/generic/src/udebug/udebug_ipc.c – Rev 2848 → 2849