include/linux/preempt.h

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