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