Remove superfluous {get|put}_task_struct() calls when iterating over tasks

Since the memory for a task_struct pointer obtained via one of the task
list loop macros is protected via RCU, and RCU read lock protection already
encapsulates LKRG's task iterations, the {get|put}_task_struct() calls are
superfluous.

Even if LKRG were to need each task_struct's refcount to be nonzero during
the task iteration, this is already guaranteed by the RCU protection. This
guarantee was added into the kernel in an old commit from 2006:
8c7904a00b06 ("[PATCH] task: RCU protect task->usage").

As such, drop the {get|put}_task_struct() calls entirely.

Signed-off-by: Sultan Alsawaf <sultan@ciq.com>

Author: kerneltoast

src/modules/exploit_detection/p_exploit_detection.c

@@ -1139,10 +1139,8 @@ static unsigned int p_iterate_processes(int (*p_func)(void *), char p_ver) {
    do_each_thread(p_ptmp, p_tmp) {
 #endif
 
-      get_task_struct(p_tmp);
       /* do not touch kernel threads or the global init */
       if (!p_is_ed_task(p_tmp)) {
-         put_task_struct(p_tmp);
          continue;
       }
 
@@ -1156,7 +1154,6 @@ static unsigned int p_iterate_processes(int (*p_func)(void *), char p_ver) {
             }
          }
       }
-      put_task_struct(p_tmp);
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 14, 0)
    }

src/modules/exploit_detection/syscalls/p_seccomp/p_seccomp.c

@@ -67,7 +67,6 @@ int p_seccomp_entry(struct kretprobe_instance *p_ri, struct pt_regs *p_regs) {
          rcu_read_lock();
          // Available since 3.14.0
          for_each_thread(p_father, p_threads) {
-            get_task_struct(p_threads);
             p_child_tmp = p_find_ed_by_pid(task_pid_nr(p_threads));
             if (p_child_tmp) {
 #ifdef P_LKRG_TASK_OFF_DEBUG
@@ -80,7 +79,6 @@ int p_seccomp_entry(struct kretprobe_instance *p_ri, struct pt_regs *p_regs) {
                p_child_tmp->p_ed_task.p_sec.flag_sync_thread = 1;
                p_set_ed_process_off(p_child_tmp);
             }
-            put_task_struct(p_threads);
          }
          rcu_read_unlock();
       } else {
@@ -118,7 +116,6 @@ int p_seccomp_ret(struct kretprobe_instance *p_ri, struct pt_regs *p_regs) {
          rcu_read_lock();
          // Available since 3.14.0
          for_each_thread(p_father, p_threads) {
-            get_task_struct(p_threads);
             p_child_tmp = p_find_ed_by_pid(task_pid_nr(p_threads));
             if (p_child_tmp) {
                if (p_update)
@@ -135,7 +132,6 @@ int p_seccomp_ret(struct kretprobe_instance *p_ri, struct pt_regs *p_regs) {
                   p_child_tmp->p_ed_task.p_sec.flag_sync_thread = 0;
                }
             }
-            put_task_struct(p_threads);
          }
          rcu_read_unlock();
       } else {