kernel/vhost_task.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2021 Oracle Corporation
   4  */
   5 #include <linux/slab.h>
   6 #include <linux/completion.h>
   7 #include <linux/sched/task.h>
   8 #include <linux/sched/vhost_task.h>
   9 #include <linux/sched/signal.h>
  10
  11 enum vhost_task_flags {
  12         VHOST_TASK_FLAGS_STOP,
  13 };
  14
  15 struct vhost_task {
  16         bool (*fn)(void *data);
  17         void *data;
  18         struct completion exited;
  19         unsigned long flags;
  20         struct task_struct *task;
  21 };
  22
  23 static int vhost_task_fn(void *data)
  24 {
  25         struct vhost_task *vtsk = data;
  26         bool dead = false;
  27
  28         for (;;) {
  29                 bool did_work;
  30
  31                 if (!dead && signal_pending(current)) {
  32                         struct ksignal ksig;
  33                         /*
  34                          * Calling get_signal will block in SIGSTOP,
  35                          * or clear fatal_signal_pending, but remember
  36                          * what was set.
  37                          *
  38                          * This thread won't actually exit until all
  39                          * of the file descriptors are closed, and
  40                          * the release function is called.
  41                          */
  42                         dead = get_signal(&ksig);
  43                         if (dead)
  44                                 clear_thread_flag(TIF_SIGPENDING);
  45                 }
  46
  47                 /* mb paired w/ vhost_task_stop */
  48                 set_current_state(TASK_INTERRUPTIBLE);
  49
  50                 if (test_bit(VHOST_TASK_FLAGS_STOP, &vtsk->flags)) {
  51                         __set_current_state(TASK_RUNNING);
  52                         break;
  53                 }
  54
  55                 did_work = vtsk->fn(vtsk->data);
  56                 if (!did_work)
  57                         schedule();
  58         }
  59
  60         complete(&vtsk->exited);
  61         do_exit(0);
  62 }
  63
  64 /**
  65  * vhost_task_wake - wakeup the vhost_task
  66  * @vtsk: vhost_task to wake
  67  *
  68  * wake up the vhost_task worker thread
  69  */
  70 void vhost_task_wake(struct vhost_task *vtsk)
  71 {
  72         wake_up_process(vtsk->task);
  73 }
  74 EXPORT_SYMBOL_GPL(vhost_task_wake);
  75
  76 /**
  77  * vhost_task_stop - stop a vhost_task
  78  * @vtsk: vhost_task to stop
  79  *
  80  * vhost_task_fn ensures the worker thread exits after
  81  * VHOST_TASK_FLAGS_SOP becomes true.
  82  */
  83 void vhost_task_stop(struct vhost_task *vtsk)
  84 {
  85         set_bit(VHOST_TASK_FLAGS_STOP, &vtsk->flags);
  86         vhost_task_wake(vtsk);
  87         /*
  88          * Make sure vhost_task_fn is no longer accessing the vhost_task before
  89          * freeing it below.
  90          */
  91         wait_for_completion(&vtsk->exited);
  92         kfree(vtsk);
  93 }
  94 EXPORT_SYMBOL_GPL(vhost_task_stop);
  95
  96 /**
  97  * vhost_task_create - create a copy of a task to be used by the kernel
  98  * @fn: vhost worker function
  99  * @arg: data to be passed to fn
 100  * @name: the thread's name
 101  *
 102  * This returns a specialized task for use by the vhost layer or NULL on
 103  * failure. The returned task is inactive, and the caller must fire it up
 104  * through vhost_task_start().
 105  */
 106 struct vhost_task *vhost_task_create(bool (*fn)(void *), void *arg,
 107                                      const char *name)
 108 {
 109         struct kernel_clone_args args = {
 110                 .flags          = CLONE_FS | CLONE_UNTRACED | CLONE_VM |
 111                                   CLONE_THREAD | CLONE_SIGHAND,
 112                 .exit_signal    = 0,
 113                 .fn             = vhost_task_fn,
 114                 .name           = name,
 115                 .user_worker    = 1,
 116                 .no_files       = 1,
 117         };
 118         struct vhost_task *vtsk;
 119         struct task_struct *tsk;
 120
 121         vtsk = kzalloc(sizeof(*vtsk), GFP_KERNEL);
 122         if (!vtsk)
 123                 return NULL;
 124         init_completion(&vtsk->exited);
 125         vtsk->data = arg;
 126         vtsk->fn = fn;
 127
 128         args.fn_arg = vtsk;
 129
 130         tsk = copy_process(NULL, 0, NUMA_NO_NODE, &args);
 131         if (IS_ERR(tsk)) {
 132                 kfree(vtsk);
 133                 return NULL;
 134         }
 135
 136         vtsk->task = tsk;
 137         return vtsk;
 138 }
 139 EXPORT_SYMBOL_GPL(vhost_task_create);
 140
 141 /**
 142  * vhost_task_start - start a vhost_task created with vhost_task_create
 143  * @vtsk: vhost_task to wake up
 144  */
 145 void vhost_task_start(struct vhost_task *vtsk)
 146 {
 147         wake_up_new_task(vtsk->task);
 148 }
 149 EXPORT_SYMBOL_GPL(vhost_task_start);