drivers/md/dm-vdo/thread-registry.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright 2023 Red Hat
   4  */
   5
   6 #include "thread-registry.h"
   7
   8 #include <asm/current.h>
   9 #include <linux/rculist.h>
  10
  11 #include "permassert.h"
  12
  13 /*
  14  * We need to be careful when using other facilities that may use thread registry functions in
  15  * their normal operation. For example, we do not want to invoke the logger while holding a lock.
  16  */
  17
  18 void vdo_initialize_thread_registry(struct thread_registry *registry)
  19 {
  20         INIT_LIST_HEAD(&registry->links);
  21         spin_lock_init(&registry->lock);
  22 }
  23
  24 /* Register the current thread and associate it with a data pointer. */
  25 void vdo_register_thread(struct thread_registry *registry,
  26                          struct registered_thread *new_thread, const void *pointer)
  27 {
  28         struct registered_thread *thread;
  29         bool found_it = false;
  30
  31         INIT_LIST_HEAD(&new_thread->links);
  32         new_thread->pointer = pointer;
  33         new_thread->task = current;
  34
  35         spin_lock(&registry->lock);
  36         list_for_each_entry(thread, &registry->links, links) {
  37                 if (thread->task == current) {
  38                         /* There should be no existing entry. */
  39                         list_del_rcu(&thread->links);
  40                         found_it = true;
  41                         break;
  42                 }
  43         }
  44         list_add_tail_rcu(&new_thread->links, &registry->links);
  45         spin_unlock(&registry->lock);
  46
  47         VDO_ASSERT_LOG_ONLY(!found_it, "new thread not already in registry");
  48         if (found_it) {
  49                 /* Ensure no RCU iterators see it before re-initializing. */
  50                 synchronize_rcu();
  51                 INIT_LIST_HEAD(&thread->links);
  52         }
  53 }
  54
  55 void vdo_unregister_thread(struct thread_registry *registry)
  56 {
  57         struct registered_thread *thread;
  58         bool found_it = false;
  59
  60         spin_lock(&registry->lock);
  61         list_for_each_entry(thread, &registry->links, links) {
  62                 if (thread->task == current) {
  63                         list_del_rcu(&thread->links);
  64                         found_it = true;
  65                         break;
  66                 }
  67         }
  68         spin_unlock(&registry->lock);
  69
  70         VDO_ASSERT_LOG_ONLY(found_it, "thread found in registry");
  71         if (found_it) {
  72                 /* Ensure no RCU iterators see it before re-initializing. */
  73                 synchronize_rcu();
  74                 INIT_LIST_HEAD(&thread->links);
  75         }
  76 }
  77
  78 const void *vdo_lookup_thread(struct thread_registry *registry)
  79 {
  80         struct registered_thread *thread;
  81         const void *result = NULL;
  82
  83         rcu_read_lock();
  84         list_for_each_entry_rcu(thread, &registry->links, links) {
  85                 if (thread->task == current) {
  86                         result = thread->pointer;
  87                         break;
  88                 }
  89         }
  90         rcu_read_unlock();
  91
  92         return result;
  93 }