kernel/task_work.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/irq_work.h>
   3 #include <linux/spinlock.h>
   4 #include <linux/task_work.h>
   5 #include <linux/resume_user_mode.h>
   6
   7 static struct callback_head work_exited; /* all we need is ->next == NULL */
   8
   9 #ifdef CONFIG_IRQ_WORK
  10 static void task_work_set_notify_irq(struct irq_work *entry)
  11 {
  12         test_and_set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
  13 }
  14 static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) =
  15         IRQ_WORK_INIT_HARD(task_work_set_notify_irq);
  16 #endif
  17
  18 /**
  19  * task_work_add - ask the @task to execute @work->func()
  20  * @task: the task which should run the callback
  21  * @work: the callback to run
  22  * @notify: how to notify the targeted task
  23  *
  24  * Queue @work for task_work_run() below and notify the @task if @notify
  25  * is @TWA_RESUME, @TWA_SIGNAL, @TWA_SIGNAL_NO_IPI or @TWA_NMI_CURRENT.
  26  *
  27  * @TWA_SIGNAL works like signals, in that the it will interrupt the targeted
  28  * task and run the task_work, regardless of whether the task is currently
  29  * running in the kernel or userspace.
  30  * @TWA_SIGNAL_NO_IPI works like @TWA_SIGNAL, except it doesn't send a
  31  * reschedule IPI to force the targeted task to reschedule and run task_work.
  32  * This can be advantageous if there's no strict requirement that the
  33  * task_work be run as soon as possible, just whenever the task enters the
  34  * kernel anyway.
  35  * @TWA_RESUME work is run only when the task exits the kernel and returns to
  36  * user mode, or before entering guest mode.
  37  * @TWA_NMI_CURRENT works like @TWA_RESUME, except it can only be used for the
  38  * current @task and if the current context is NMI.
  39  *
  40  * Fails if the @task is exiting/exited and thus it can't process this @work.
  41  * Otherwise @work->func() will be called when the @task goes through one of
  42  * the aforementioned transitions, or exits.
  43  *
  44  * If the targeted task is exiting, then an error is returned and the work item
  45  * is not queued. It's up to the caller to arrange for an alternative mechanism
  46  * in that case.
  47  *
  48  * Note: there is no ordering guarantee on works queued here. The task_work
  49  * list is LIFO.
  50  *
  51  * RETURNS:
  52  * 0 if succeeds or -ESRCH.
  53  */
  54 int task_work_add(struct task_struct *task, struct callback_head *work,
  55                   enum task_work_notify_mode notify)
  56 {
  57         struct callback_head *head;
  58         int flags = notify & TWA_FLAGS;
  59
  60         notify &= ~TWA_FLAGS;
  61         if (notify == TWA_NMI_CURRENT) {
  62                 if (WARN_ON_ONCE(task != current))
  63                         return -EINVAL;
  64                 if (!IS_ENABLED(CONFIG_IRQ_WORK))
  65                         return -EINVAL;
  66         } else {
  67                 /*
  68                  * Record the work call stack in order to print it in KASAN
  69                  * reports.
  70                  *
  71                  * Note that stack allocation can fail if TWAF_NO_ALLOC flag
  72                  * is set and new page is needed to expand the stack buffer.
  73                  */
  74                 if (flags & TWAF_NO_ALLOC)
  75                         kasan_record_aux_stack_noalloc(work);
  76                 else
  77                         kasan_record_aux_stack(work);
  78         }
  79
  80         head = READ_ONCE(task->task_works);
  81         do {
  82                 if (unlikely(head == &work_exited))
  83                         return -ESRCH;
  84                 work->next = head;
  85         } while (!try_cmpxchg(&task->task_works, &head, work));
  86
  87         switch (notify) {
  88         case TWA_NONE:
  89                 break;
  90         case TWA_RESUME:
  91                 set_notify_resume(task);
  92                 break;
  93         case TWA_SIGNAL:
  94                 set_notify_signal(task);
  95                 break;
  96         case TWA_SIGNAL_NO_IPI:
  97                 __set_notify_signal(task);
  98                 break;
  99 #ifdef CONFIG_IRQ_WORK
 100         case TWA_NMI_CURRENT:
 101                 irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume));
 102                 break;
 103 #endif
 104         default:
 105                 WARN_ON_ONCE(1);
 106                 break;
 107         }
 108
 109         return 0;
 110 }
 111
 112 /**
 113  * task_work_cancel_match - cancel a pending work added by task_work_add()
 114  * @task: the task which should execute the work
 115  * @match: match function to call
 116  * @data: data to be passed in to match function
 117  *
 118  * RETURNS:
 119  * The found work or NULL if not found.
 120  */
 121 struct callback_head *
 122 task_work_cancel_match(struct task_struct *task,
 123                        bool (*match)(struct callback_head *, void *data),
 124                        void *data)
 125 {
 126         struct callback_head **pprev = &task->task_works;
 127         struct callback_head *work;
 128         unsigned long flags;
 129
 130         if (likely(!task_work_pending(task)))
 131                 return NULL;
 132         /*
 133          * If cmpxchg() fails we continue without updating pprev.
 134          * Either we raced with task_work_add() which added the
 135          * new entry before this work, we will find it again. Or
 136          * we raced with task_work_run(), *pprev == NULL/exited.
 137          */
 138         raw_spin_lock_irqsave(&task->pi_lock, flags);
 139         work = READ_ONCE(*pprev);
 140         while (work) {
 141                 if (!match(work, data)) {
 142                         pprev = &work->next;
 143                         work = READ_ONCE(*pprev);
 144                 } else if (try_cmpxchg(pprev, &work, work->next))
 145                         break;
 146         }
 147         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 148
 149         return work;
 150 }
 151
 152 static bool task_work_func_match(struct callback_head *cb, void *data)
 153 {
 154         return cb->func == data;
 155 }
 156
 157 /**
 158  * task_work_cancel_func - cancel a pending work matching a function added by task_work_add()
 159  * @task: the task which should execute the func's work
 160  * @func: identifies the func to match with a work to remove
 161  *
 162  * Find the last queued pending work with ->func == @func and remove
 163  * it from queue.
 164  *
 165  * RETURNS:
 166  * The found work or NULL if not found.
 167  */
 168 struct callback_head *
 169 task_work_cancel_func(struct task_struct *task, task_work_func_t func)
 170 {
 171         return task_work_cancel_match(task, task_work_func_match, func);
 172 }
 173
 174 static bool task_work_match(struct callback_head *cb, void *data)
 175 {
 176         return cb == data;
 177 }
 178
 179 /**
 180  * task_work_cancel - cancel a pending work added by task_work_add()
 181  * @task: the task which should execute the work
 182  * @cb: the callback to remove if queued
 183  *
 184  * Remove a callback from a task's queue if queued.
 185  *
 186  * RETURNS:
 187  * True if the callback was queued and got cancelled, false otherwise.
 188  */
 189 bool task_work_cancel(struct task_struct *task, struct callback_head *cb)
 190 {
 191         struct callback_head *ret;
 192
 193         ret = task_work_cancel_match(task, task_work_match, cb);
 194
 195         return ret == cb;
 196 }
 197
 198 /**
 199  * task_work_run - execute the works added by task_work_add()
 200  *
 201  * Flush the pending works. Should be used by the core kernel code.
 202  * Called before the task returns to the user-mode or stops, or when
 203  * it exits. In the latter case task_work_add() can no longer add the
 204  * new work after task_work_run() returns.
 205  */
 206 void task_work_run(void)
 207 {
 208         struct task_struct *task = current;
 209         struct callback_head *work, *head, *next;
 210
 211         for (;;) {
 212                 /*
 213                  * work->func() can do task_work_add(), do not set
 214                  * work_exited unless the list is empty.
 215                  */
 216                 work = READ_ONCE(task->task_works);
 217                 do {
 218                         head = NULL;
 219                         if (!work) {
 220                                 if (task->flags & PF_EXITING)
 221                                         head = &work_exited;
 222                                 else
 223                                         break;
 224                         }
 225                 } while (!try_cmpxchg(&task->task_works, &work, head));
 226
 227                 if (!work)
 228                         break;
 229                 /*
 230                  * Synchronize with task_work_cancel_match(). It can not remove
 231                  * the first entry == work, cmpxchg(task_works) must fail.
 232                  * But it can remove another entry from the ->next list.
 233                  */
 234                 raw_spin_lock_irq(&task->pi_lock);
 235                 raw_spin_unlock_irq(&task->pi_lock);
 236
 237                 do {
 238                         next = work->next;
 239                         work->func(work);
 240                         work = next;
 241                         cond_resched();
 242                 } while (work);
 243         }
 244 }