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 /* preempt_count() and related functions, depends on PREEMPT_NEED_RESCHED */
  59 #include <asm/preempt.h>
  60
  61 #define hardirq_count() (preempt_count() & HARDIRQ_MASK)
  62 #define softirq_count() (preempt_count() & SOFTIRQ_MASK)
  63 #define irq_count()     (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK \
  64                                  | NMI_MASK))
  65
  66 /*
  67  * Are we doing bottom half or hardware interrupt processing?
  68  *
  69  * in_irq()       - We're in (hard) IRQ context
  70  * in_softirq()   - We have BH disabled, or are processing softirqs
  71  * in_interrupt() - We're in NMI,IRQ,SoftIRQ context or have BH disabled
  72  * in_serving_softirq() - We're in softirq context
  73  * in_nmi()       - We're in NMI context
  74  * in_task()      - We're in task context
  75  *
  76  * Note: due to the BH disabled confusion: in_softirq(),in_interrupt() really
  77  *       should not be used in new code.
  78  */
  79 #define in_irq()                (hardirq_count())
  80 #define in_softirq()            (softirq_count())
  81 #define in_interrupt()          (irq_count())
  82 #define in_serving_softirq()    (softirq_count() & SOFTIRQ_OFFSET)
  83 #define in_nmi()                (preempt_count() & NMI_MASK)
  84 #define in_task()               (!(preempt_count() & \
  85                                    (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
  86
  87 /*
  88  * The preempt_count offset after preempt_disable();
  89  */
  90 #if defined(CONFIG_PREEMPT_COUNT)
  91 # define PREEMPT_DISABLE_OFFSET PREEMPT_OFFSET
  92 #else
  93 # define PREEMPT_DISABLE_OFFSET 0
  94 #endif
  95
  96 /*
  97  * The preempt_count offset after spin_lock()
  98  */
  99 #define PREEMPT_LOCK_OFFSET     PREEMPT_DISABLE_OFFSET
 100
 101 /*
 102  * The preempt_count offset needed for things like:
 103  *
 104  *  spin_lock_bh()
 105  *
 106  * Which need to disable both preemption (CONFIG_PREEMPT_COUNT) and
 107  * softirqs, such that unlock sequences of:
 108  *
 109  *  spin_unlock();
 110  *  local_bh_enable();
 111  *
 112  * Work as expected.
 113  */
 114 #define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_LOCK_OFFSET)
 115
 116 /*
 117  * Are we running in atomic context?  WARNING: this macro cannot
 118  * always detect atomic context; in particular, it cannot know about
 119  * held spinlocks in non-preemptible kernels.  Thus it should not be
 120  * used in the general case to determine whether sleeping is possible.
 121  * Do not use in_atomic() in driver code.
 122  */
 123 #define in_atomic()     (preempt_count() != 0)
 124
 125 /*
 126  * Check whether we were atomic before we did preempt_disable():
 127  * (used by the scheduler)
 128  */
 129 #define in_atomic_preempt_off() (preempt_count() != PREEMPT_DISABLE_OFFSET)
 130
 131 #if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
 132 extern void preempt_count_add(int val);
 133 extern void preempt_count_sub(int val);
 134 #define preempt_count_dec_and_test() \
 135         ({ preempt_count_sub(1); should_resched(0); })
 136 #else
 137 #define preempt_count_add(val)  __preempt_count_add(val)
 138 #define preempt_count_sub(val)  __preempt_count_sub(val)
 139 #define preempt_count_dec_and_test() __preempt_count_dec_and_test()
 140 #endif
 141
 142 #define __preempt_count_inc() __preempt_count_add(1)
 143 #define __preempt_count_dec() __preempt_count_sub(1)
 144
 145 #define preempt_count_inc() preempt_count_add(1)
 146 #define preempt_count_dec() preempt_count_sub(1)
 147
 148 #ifdef CONFIG_PREEMPT_COUNT
 149
 150 #define preempt_disable() \
 151 do { \
 152         preempt_count_inc(); \
 153         barrier(); \
 154 } while (0)
 155
 156 #define sched_preempt_enable_no_resched() \
 157 do { \
 158         barrier(); \
 159         preempt_count_dec(); \
 160 } while (0)
 161
 162 #define preempt_enable_no_resched() sched_preempt_enable_no_resched()
 163
 164 #define preemptible()   (preempt_count() == 0 && !irqs_disabled())
 165
 166 #ifdef CONFIG_PREEMPT
 167 #define preempt_enable() \
 168 do { \
 169         barrier(); \
 170         if (unlikely(preempt_count_dec_and_test())) \
 171                 __preempt_schedule(); \
 172 } while (0)
 173
 174 #define preempt_enable_notrace() \
 175 do { \
 176         barrier(); \
 177         if (unlikely(__preempt_count_dec_and_test())) \
 178                 __preempt_schedule_notrace(); \
 179 } while (0)
 180
 181 #define preempt_check_resched() \
 182 do { \
 183         if (should_resched(0)) \
 184                 __preempt_schedule(); \
 185 } while (0)
 186
 187 #else /* !CONFIG_PREEMPT */
 188 #define preempt_enable() \
 189 do { \
 190         barrier(); \
 191         preempt_count_dec(); \
 192 } while (0)
 193
 194 #define preempt_enable_notrace() \
 195 do { \
 196         barrier(); \
 197         __preempt_count_dec(); \
 198 } while (0)
 199
 200 #define preempt_check_resched() do { } while (0)
 201 #endif /* CONFIG_PREEMPT */
 202
 203 #define preempt_disable_notrace() \
 204 do { \
 205         __preempt_count_inc(); \
 206         barrier(); \
 207 } while (0)
 208
 209 #define preempt_enable_no_resched_notrace() \
 210 do { \
 211         barrier(); \
 212         __preempt_count_dec(); \
 213 } while (0)
 214
 215 #else /* !CONFIG_PREEMPT_COUNT */
 216
 217 /*
 218  * Even if we don't have any preemption, we need preempt disable/enable
 219  * to be barriers, so that we don't have things like get_user/put_user
 220  * that can cause faults and scheduling migrate into our preempt-protected
 221  * region.
 222  */
 223 #define preempt_disable()                       barrier()
 224 #define sched_preempt_enable_no_resched()       barrier()
 225 #define preempt_enable_no_resched()             barrier()
 226 #define preempt_enable()                        barrier()
 227 #define preempt_check_resched()                 do { } while (0)
 228
 229 #define preempt_disable_notrace()               barrier()
 230 #define preempt_enable_no_resched_notrace()     barrier()
 231 #define preempt_enable_notrace()                barrier()
 232 #define preemptible()                           0
 233
 234 #endif /* CONFIG_PREEMPT_COUNT */
 235
 236 #ifdef MODULE
 237 /*
 238  * Modules have no business playing preemption tricks.
 239  */
 240 #undef sched_preempt_enable_no_resched
 241 #undef preempt_enable_no_resched
 242 #undef preempt_enable_no_resched_notrace
 243 #undef preempt_check_resched
 244 #endif
 245
 246 #define preempt_set_need_resched() \
 247 do { \
 248         set_preempt_need_resched(); \
 249 } while (0)
 250 #define preempt_fold_need_resched() \
 251 do { \
 252         if (tif_need_resched()) \
 253                 set_preempt_need_resched(); \
 254 } while (0)
 255
 256 #ifdef CONFIG_PREEMPT_NOTIFIERS
 257
 258 struct preempt_notifier;
 259
 260 /**
 261  * preempt_ops - notifiers called when a task is preempted and rescheduled
 262  * @sched_in: we're about to be rescheduled:
 263  *    notifier: struct preempt_notifier for the task being scheduled
 264  *    cpu:  cpu we're scheduled on
 265  * @sched_out: we've just been preempted
 266  *    notifier: struct preempt_notifier for the task being preempted
 267  *    next: the task that's kicking us out
 268  *
 269  * Please note that sched_in and out are called under different
 270  * contexts.  sched_out is called with rq lock held and irq disabled
 271  * while sched_in is called without rq lock and irq enabled.  This
 272  * difference is intentional and depended upon by its users.
 273  */
 274 struct preempt_ops {
 275         void (*sched_in)(struct preempt_notifier *notifier, int cpu);
 276         void (*sched_out)(struct preempt_notifier *notifier,
 277                           struct task_struct *next);
 278 };
 279
 280 /**
 281  * preempt_notifier - key for installing preemption notifiers
 282  * @link: internal use
 283  * @ops: defines the notifier functions to be called
 284  *
 285  * Usually used in conjunction with container_of().
 286  */
 287 struct preempt_notifier {
 288         struct hlist_node link;
 289         struct preempt_ops *ops;
 290 };
 291
 292 void preempt_notifier_inc(void);
 293 void preempt_notifier_dec(void);
 294 void preempt_notifier_register(struct preempt_notifier *notifier);
 295 void preempt_notifier_unregister(struct preempt_notifier *notifier);
 296
 297 static inline void preempt_notifier_init(struct preempt_notifier *notifier,
 298                                      struct preempt_ops *ops)
 299 {
 300         INIT_HLIST_NODE(&notifier->link);
 301         notifier->ops = ops;
 302 }
 303
 304 #endif
 305
 306 #endif /* __LINUX_PREEMPT_H */