include/linux/preempt.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef __LINUX_PREEMPT_H
   3 #define __LINUX_PREEMPT_H
   4
   5 /*
   6  * include/linux/preempt.h - macros for accessing and manipulating
   7  * preempt_count (used for kernel preemption, interrupt count, etc.)
   8  */
   9
  10 #include <linux/linkage.h>
  11 #include <linux/list.h>
  12
  13 /*
  14  * We put the hardirq and softirq counter into the preemption
  15  * counter. The bitmask has the following meaning:
  16  *
  17  * - bits 0-7 are the preemption count (max preemption depth: 256)
  18  * - bits 8-15 are the softirq count (max # of softirqs: 256)
  19  *
  20  * The hardirq count could in theory be the same as the number of
  21  * interrupts in the system, but we run all interrupt handlers with
  22  * interrupts disabled, so we cannot have nesting interrupts. Though
  23  * there are a few palaeontologic drivers which reenable interrupts in
  24  * the handler, so we need more than one bit here.
  25  *
  26  *         PREEMPT_MASK:        0x000000ff
  27  *         SOFTIRQ_MASK:        0x0000ff00
  28  *         HARDIRQ_MASK:        0x000f0000
  29  *             NMI_MASK:        0x00100000
  30  * PREEMPT_NEED_RESCHED:        0x80000000
  31  */
  32 #define PREEMPT_BITS    8
  33 #define SOFTIRQ_BITS    8
  34 #define HARDIRQ_BITS    4
  35 #define NMI_BITS        1
  36
  37 #define PREEMPT_SHIFT   0
  38 #define SOFTIRQ_SHIFT   (PREEMPT_SHIFT + PREEMPT_BITS)
  39 #define HARDIRQ_SHIFT   (SOFTIRQ_SHIFT + SOFTIRQ_BITS)
  40 #define NMI_SHIFT       (HARDIRQ_SHIFT + HARDIRQ_BITS)
  41
  42 #define __IRQ_MASK(x)   ((1UL << (x))-1)
  43
  44 #define PREEMPT_MASK    (__IRQ_MASK(PREEMPT_BITS) << PREEMPT_SHIFT)
  45 #define SOFTIRQ_MASK    (__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)
  46 #define HARDIRQ_MASK    (__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)
  47 #define NMI_MASK        (__IRQ_MASK(NMI_BITS)     << NMI_SHIFT)
  48
  49 #define PREEMPT_OFFSET  (1UL << PREEMPT_SHIFT)
  50 #define SOFTIRQ_OFFSET  (1UL << SOFTIRQ_SHIFT)
  51 #define HARDIRQ_OFFSET  (1UL << HARDIRQ_SHIFT)
  52 #define NMI_OFFSET      (1UL << NMI_SHIFT)
  53
  54 #define SOFTIRQ_DISABLE_OFFSET  (2 * SOFTIRQ_OFFSET)
  55
  56 /* We use the MSB mostly because its available */
  57 #define PREEMPT_NEED_RESCHED    0x80000000
  58
  59 #define PREEMPT_DISABLED        (PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)
  60
  61 /*
  62  * Disable preemption until the scheduler is running -- use an unconditional
  63  * value so that it also works on !PREEMPT_COUNT kernels.
  64  *
  65  * Reset by start_kernel()->sched_init()->init_idle()->init_idle_preempt_count().
  66  */
  67 #define INIT_PREEMPT_COUNT      PREEMPT_OFFSET
  68
  69 /*
  70  * Initial preempt_count value; reflects the preempt_count schedule invariant
  71  * which states that during context switches:
  72  *
  73  *    preempt_count() == 2*PREEMPT_DISABLE_OFFSET
  74  *
  75  * Note: PREEMPT_DISABLE_OFFSET is 0 for !PREEMPT_COUNT kernels.
  76  * Note: See finish_task_switch().
  77  */
  78 #define FORK_PREEMPT_COUNT      (2*PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)
  79
  80 /* preempt_count() and related functions, depends on PREEMPT_NEED_RESCHED */
  81 #include <asm/preempt.h>
  82
  83 #define hardirq_count() (preempt_count() & HARDIRQ_MASK)
  84 #define softirq_count() (preempt_count() & SOFTIRQ_MASK)
  85 #define irq_count()     (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK \
  86                                  | NMI_MASK))
  87
  88 /*
  89  * Are we doing bottom half or hardware interrupt processing?
  90  *
  91  * in_irq()       - We're in (hard) IRQ context
  92  * in_softirq()   - We have BH disabled, or are processing softirqs
  93  * in_interrupt() - We're in NMI,IRQ,SoftIRQ context or have BH disabled
  94  * in_serving_softirq() - We're in softirq context
  95  * in_nmi()       - We're in NMI context
  96  * in_task()      - We're in task context
  97  *
  98  * Note: due to the BH disabled confusion: in_softirq(),in_interrupt() really
  99  *       should not be used in new code.
 100  */
 101 #define in_irq()                (hardirq_count())
 102 #define in_softirq()            (softirq_count())
 103 #define in_interrupt()          (irq_count())
 104 #define in_serving_softirq()    (softirq_count() & SOFTIRQ_OFFSET)
 105 #define in_nmi()                (preempt_count() & NMI_MASK)
 106 #define in_task()               (!(preempt_count() & \
 107                                    (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
 108
 109 /*
 110  * The preempt_count offset after preempt_disable();
 111  */
 112 #if defined(CONFIG_PREEMPT_COUNT)
 113 # define PREEMPT_DISABLE_OFFSET PREEMPT_OFFSET
 114 #else
 115 # define PREEMPT_DISABLE_OFFSET 0
 116 #endif
 117
 118 /*
 119  * The preempt_count offset after spin_lock()
 120  */
 121 #define PREEMPT_LOCK_OFFSET     PREEMPT_DISABLE_OFFSET
 122
 123 /*
 124  * The preempt_count offset needed for things like:
 125  *
 126  *  spin_lock_bh()
 127  *
 128  * Which need to disable both preemption (CONFIG_PREEMPT_COUNT) and
 129  * softirqs, such that unlock sequences of:
 130  *
 131  *  spin_unlock();
 132  *  local_bh_enable();
 133  *
 134  * Work as expected.
 135  */
 136 #define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_LOCK_OFFSET)
 137
 138 /*
 139  * Are we running in atomic context?  WARNING: this macro cannot
 140  * always detect atomic context; in particular, it cannot know about
 141  * held spinlocks in non-preemptible kernels.  Thus it should not be
 142  * used in the general case to determine whether sleeping is possible.
 143  * Do not use in_atomic() in driver code.
 144  */
 145 #define in_atomic()     (preempt_count() != 0)
 146
 147 /*
 148  * Check whether we were atomic before we did preempt_disable():
 149  * (used by the scheduler)
 150  */
 151 #define in_atomic_preempt_off() (preempt_count() != PREEMPT_DISABLE_OFFSET)
 152
 153 #if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
 154 extern void preempt_count_add(int val);
 155 extern void preempt_count_sub(int val);
 156 #define preempt_count_dec_and_test() \
 157         ({ preempt_count_sub(1); should_resched(0); })
 158 #else
 159 #define preempt_count_add(val)  __preempt_count_add(val)
 160 #define preempt_count_sub(val)  __preempt_count_sub(val)
 161 #define preempt_count_dec_and_test() __preempt_count_dec_and_test()
 162 #endif
 163
 164 #define __preempt_count_inc() __preempt_count_add(1)
 165 #define __preempt_count_dec() __preempt_count_sub(1)
 166
 167 #define preempt_count_inc() preempt_count_add(1)
 168 #define preempt_count_dec() preempt_count_sub(1)
 169
 170 #ifdef CONFIG_PREEMPT_COUNT
 171
 172 #define preempt_disable() \
 173 do { \
 174         preempt_count_inc(); \
 175         barrier(); \
 176 } while (0)
 177
 178 #define sched_preempt_enable_no_resched() \
 179 do { \
 180         barrier(); \
 181         preempt_count_dec(); \
 182 } while (0)
 183
 184 #define preempt_enable_no_resched() sched_preempt_enable_no_resched()
 185
 186 #define preemptible()   (preempt_count() == 0 && !irqs_disabled())
 187
 188 #ifdef CONFIG_PREEMPT
 189 #define preempt_enable() \
 190 do { \
 191         barrier(); \
 192         if (unlikely(preempt_count_dec_and_test())) \
 193                 __preempt_schedule(); \
 194 } while (0)
 195
 196 #define preempt_enable_notrace() \
 197 do { \
 198         barrier(); \
 199         if (unlikely(__preempt_count_dec_and_test())) \
 200                 __preempt_schedule_notrace(); \
 201 } while (0)
 202
 203 #define preempt_check_resched() \
 204 do { \
 205         if (should_resched(0)) \
 206                 __preempt_schedule(); \
 207 } while (0)
 208
 209 #else /* !CONFIG_PREEMPT */
 210 #define preempt_enable() \
 211 do { \
 212         barrier(); \
 213         preempt_count_dec(); \
 214 } while (0)
 215
 216 #define preempt_enable_notrace() \
 217 do { \
 218         barrier(); \
 219         __preempt_count_dec(); \
 220 } while (0)
 221
 222 #define preempt_check_resched() do { } while (0)
 223 #endif /* CONFIG_PREEMPT */
 224
 225 #define preempt_disable_notrace() \
 226 do { \
 227         __preempt_count_inc(); \
 228         barrier(); \
 229 } while (0)
 230
 231 #define preempt_enable_no_resched_notrace() \
 232 do { \
 233         barrier(); \
 234         __preempt_count_dec(); \
 235 } while (0)
 236
 237 #else /* !CONFIG_PREEMPT_COUNT */
 238
 239 /*
 240  * Even if we don't have any preemption, we need preempt disable/enable
 241  * to be barriers, so that we don't have things like get_user/put_user
 242  * that can cause faults and scheduling migrate into our preempt-protected
 243  * region.
 244  */
 245 #define preempt_disable()                       barrier()
 246 #define sched_preempt_enable_no_resched()       barrier()
 247 #define preempt_enable_no_resched()             barrier()
 248 #define preempt_enable()                        barrier()
 249 #define preempt_check_resched()                 do { } while (0)
 250
 251 #define preempt_disable_notrace()               barrier()
 252 #define preempt_enable_no_resched_notrace()     barrier()
 253 #define preempt_enable_notrace()                barrier()
 254 #define preemptible()                           0
 255
 256 #endif /* CONFIG_PREEMPT_COUNT */
 257
 258 #ifdef MODULE
 259 /*
 260  * Modules have no business playing preemption tricks.
 261  */
 262 #undef sched_preempt_enable_no_resched
 263 #undef preempt_enable_no_resched
 264 #undef preempt_enable_no_resched_notrace
 265 #undef preempt_check_resched
 266 #endif
 267
 268 #define preempt_set_need_resched() \
 269 do { \
 270         set_preempt_need_resched(); \
 271 } while (0)
 272 #define preempt_fold_need_resched() \
 273 do { \
 274         if (tif_need_resched()) \
 275                 set_preempt_need_resched(); \
 276 } while (0)
 277
 278 #ifdef CONFIG_PREEMPT_NOTIFIERS
 279
 280 struct preempt_notifier;
 281
 282 /**
 283  * preempt_ops - notifiers called when a task is preempted and rescheduled
 284  * @sched_in: we're about to be rescheduled:
 285  *    notifier: struct preempt_notifier for the task being scheduled
 286  *    cpu:  cpu we're scheduled on
 287  * @sched_out: we've just been preempted
 288  *    notifier: struct preempt_notifier for the task being preempted
 289  *    next: the task that's kicking us out
 290  *
 291  * Please note that sched_in and out are called under different
 292  * contexts.  sched_out is called with rq lock held and irq disabled
 293  * while sched_in is called without rq lock and irq enabled.  This
 294  * difference is intentional and depended upon by its users.
 295  */
 296 struct preempt_ops {
 297         void (*sched_in)(struct preempt_notifier *notifier, int cpu);
 298         void (*sched_out)(struct preempt_notifier *notifier,
 299                           struct task_struct *next);
 300 };
 301
 302 /**
 303  * preempt_notifier - key for installing preemption notifiers
 304  * @link: internal use
 305  * @ops: defines the notifier functions to be called
 306  *
 307  * Usually used in conjunction with container_of().
 308  */
 309 struct preempt_notifier {
 310         struct hlist_node link;
 311         struct preempt_ops *ops;
 312 };
 313
 314 void preempt_notifier_inc(void);
 315 void preempt_notifier_dec(void);
 316 void preempt_notifier_register(struct preempt_notifier *notifier);
 317 void preempt_notifier_unregister(struct preempt_notifier *notifier);
 318
 319 static inline void preempt_notifier_init(struct preempt_notifier *notifier,
 320                                      struct preempt_ops *ops)
 321 {
 322         INIT_HLIST_NODE(&notifier->link);
 323         notifier->ops = ops;
 324 }
 325
 326 #endif
 327
 328 #endif /* __LINUX_PREEMPT_H */