| 1 | |
| 2 | |
| 3 | * Copyright (C) 2008 Red Hat, Inc., Eric Paris <[email protected]>
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| 4 |
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| 5 |
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| 6 | |
| 7 | * Basic idea behind the notification queue: An fsnotify group (like inotify)
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| 8 | * sends the userspace notification about events asynchronously some time after
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| 9 | * the event happened. When inotify gets an event it will need to add that
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| 10 | * event to the group notify queue. Since a single event might need to be on
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| 11 | * multiple group's notification queues we can't add the event directly to each
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| 12 | * queue and instead add a small "event_holder" to each queue. This event_holder
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| 13 | * has a pointer back to the original event. Since the majority of events are
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| 14 | * going to end up on one, and only one, notification queue we embed one
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| 15 | * event_holder into each event. This means we have a single allocation instead
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| 16 | * of always needing two. If the embedded event_holder is already in use by
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| 17 | * another group a new event_holder (from fsnotify_event_holder_cachep) will be
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| 18 | * allocated and used.
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| 19 |
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| 20 |
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| 21 | #include <linux/fs.h>
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| 22 | #include <linux/init.h>
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| 23 | #include <linux/kernel.h>
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| 24 | #include <linux/list.h>
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| 25 | #include <linux/module.h>
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| 26 | #include <linux/mount.h>
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| 27 | #include <linux/mutex.h>
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| 28 | #include <linux/namei.h>
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| 29 | #include <linux/path.h>
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| 30 | #include <linux/slab.h>
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| 31 | #include <linux/spinlock.h>
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| 32 |
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| 33 | #include <linux/atomic.h>
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| 34 |
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| 35 | #include <linux/fsnotify_backend.h>
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| 36 | #include "fsnotify.h"
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| 37 |
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| 38 | static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);
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| 39 |
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| 40 | |
| 41 | * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
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| 42 | * Called from fsnotify_move, which is inlined into filesystem modules.
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| 43 |
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| 44 | u32 fsnotify_get_cookie(void)
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| 45 | {
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| 46 | return atomic_inc_return(&fsnotify_sync_cookie);
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| 47 | }
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| 48 | EXPORT_SYMBOL_GPL(fsnotify_get_cookie);
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| 49 |
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| 50 | void fsnotify_destroy_event(struct fsnotify_group *group,
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| 51 | struct fsnotify_event *event)
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| 52 | {
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| 53 |
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| 54 | if (!event || event == group->overflow_event)
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| 55 | return;
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| 56 | |
| 57 | * If the event is still queued, we have a problem... Do an unreliable
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| 58 | * lockless check first to avoid locking in the common case. The
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| 59 | * locking may be necessary for permission events which got removed
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| 60 | * from the list by a different CPU than the one freeing the event.
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| 61 |
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| 62 | if (!list_empty(&event->list)) {
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| 63 | spin_lock(&group->notification_lock);
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| 64 | WARN_ON(!list_empty(&event->list));
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| 65 | spin_unlock(&group->notification_lock);
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| 66 | }
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| 67 | group->ops->free_event(group, event);
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| 68 | }
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| 69 |
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| 70 | |
| 71 | * Try to add an event to the notification queue.
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| 72 | * The group can later pull this event off the queue to deal with.
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| 73 | * The group can use the @merge hook to merge the event with a queued event.
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| 74 | * The group can use the @insert hook to insert the event into hash table.
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| 75 | * The function returns:
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| 76 | * 0 if the event was added to a queue
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| 77 | * 1 if the event was merged with some other queued event
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| 78 | * 2 if the event was not queued - either the queue of events has overflown
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| 79 | * or the group is shutting down.
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| 80 |
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| 81 | int fsnotify_insert_event(struct fsnotify_group *group,
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| 82 | struct fsnotify_event *event,
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| 83 | int (*merge)(struct fsnotify_group *,
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| 84 | struct fsnotify_event *),
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| 85 | void (*insert)(struct fsnotify_group *,
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| 86 | struct fsnotify_event *))
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| 87 | {
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| 88 | int ret = 0;
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| 89 | struct list_head *list = &group->notification_list;
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| 90 |
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| 91 | pr_debug("%s: group=%p event=%p\n", __func__, group, event);
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| 92 |
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| 93 | spin_lock(&group->notification_lock);
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| 94 |
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| 95 | if (group->shutdown) {
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| 96 | spin_unlock(&group->notification_lock);
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| 97 | return 2;
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| 98 | }
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| 99 |
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| 100 | if (event == group->overflow_event ||
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| 101 | group->q_len >= group->max_events) {
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| 102 | ret = 2;
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| 103 |
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| 104 | if (!list_empty(&group->overflow_event->list)) {
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| 105 | spin_unlock(&group->notification_lock);
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| 106 | return ret;
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| 107 | }
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| 108 | event = group->overflow_event;
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| 109 | goto queue;
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| 110 | }
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| 111 |
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| 112 | if (!list_empty(list) && merge) {
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| 113 | ret = merge(group, event);
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| 114 | if (ret) {
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| 115 | spin_unlock(&group->notification_lock);
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| 116 | return ret;
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| 117 | }
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| 118 | }
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| 119 |
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| 120 | queue:
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| 121 | group->q_len++;
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| 122 | list_add_tail(&event->list, list);
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| 123 | if (insert)
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| 124 | insert(group, event);
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| 125 | spin_unlock(&group->notification_lock);
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| 126 |
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| 127 | wake_up(&group->notification_waitq);
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| 128 | kill_fasync(&group->fsn_fa, SIGIO, POLL_IN);
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| 129 | return ret;
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| 130 | }
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| 131 |
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| 132 | void fsnotify_remove_queued_event(struct fsnotify_group *group,
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| 133 | struct fsnotify_event *event)
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| 134 | {
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| 135 | assert_spin_locked(&group->notification_lock);
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| 136 | |
| 137 | * We need to init list head for the case of overflow event so that
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| 138 | * check in fsnotify_add_event() works
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| 139 |
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| 140 | list_del_init(&event->list);
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| 141 | group->q_len--;
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| 142 | }
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| 143 |
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| 144 | |
| 145 | * Return the first event on the notification list without removing it.
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| 146 | * Returns NULL if the list is empty.
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| 147 |
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| 148 | struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group)
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| 149 | {
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| 150 | assert_spin_locked(&group->notification_lock);
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| 151 |
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| 152 | if (fsnotify_notify_queue_is_empty(group))
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| 153 | return NULL;
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| 154 |
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| 155 | return list_first_entry(&group->notification_list,
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| 156 | struct fsnotify_event, list);
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| 157 | }
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| 158 |
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| 159 | |
| 160 | * Remove and return the first event from the notification list. It is the
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| 161 | * responsibility of the caller to destroy the obtained event
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| 162 |
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| 163 | struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group)
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| 164 | {
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| 165 | struct fsnotify_event *event = fsnotify_peek_first_event(group);
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| 166 |
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| 167 | if (!event)
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| 168 | return NULL;
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| 169 |
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| 170 | pr_debug("%s: group=%p event=%p\n", __func__, group, event);
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| 171 |
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| 172 | fsnotify_remove_queued_event(group, event);
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| 173 |
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| 174 | return event;
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| 175 | }
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| 176 |
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| 177 | |
| 178 | * Called when a group is being torn down to clean up any outstanding
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| 179 | * event notifications.
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| 180 |
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| 181 | void fsnotify_flush_notify(struct fsnotify_group *group)
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| 182 | {
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| 183 | struct fsnotify_event *event;
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| 184 |
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| 185 | spin_lock(&group->notification_lock);
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| 186 | while (!fsnotify_notify_queue_is_empty(group)) {
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| 187 | event = fsnotify_remove_first_event(group);
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| 188 | spin_unlock(&group->notification_lock);
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| 189 | fsnotify_destroy_event(group, event);
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| 190 | spin_lock(&group->notification_lock);
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| 191 | }
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| 192 | spin_unlock(&group->notification_lock);
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| 193 | }
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