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_ACTIVE:        0x00200000
  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 #define PREEMPT_ACTIVE_BITS     1
  57 #define PREEMPT_ACTIVE_SHIFT    (NMI_SHIFT + NMI_BITS)
  58 #define PREEMPT_ACTIVE  (__IRQ_MASK(PREEMPT_ACTIVE_BITS) << PREEMPT_ACTIVE_SHIFT)
  59
  60 /* We use the MSB mostly because its available */
  61 #define PREEMPT_NEED_RESCHED    0x80000000
  62
  63 /* preempt_count() and related functions, depends on PREEMPT_NEED_RESCHED */
  64 #include <asm/preempt.h>
  65
  66 #define hardirq_count() (preempt_count() & HARDIRQ_MASK)
  67 #define softirq_count() (preempt_count() & SOFTIRQ_MASK)
  68 #define irq_count()     (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK \
  69                                  | NMI_MASK))
  70
  71 /*
  72  * Are we doing bottom half or hardware interrupt processing?
  73  * Are we in a softirq context? Interrupt context?
  74  * in_softirq - Are we currently processing softirq or have bh disabled?
  75  * in_serving_softirq - Are we currently processing softirq?
  76  */
  77 #define in_irq()                (hardirq_count())
  78 #define in_softirq()            (softirq_count())
  79 #define in_interrupt()          (irq_count())
  80 #define in_serving_softirq()    (softirq_count() & SOFTIRQ_OFFSET)
  81
  82 /*
  83  * Are we in NMI context?
  84  */
  85 #define in_nmi()        (preempt_count() & NMI_MASK)
  86
  87 #if defined(CONFIG_PREEMPT_COUNT)
  88 # define PREEMPT_DISABLE_OFFSET 1
  89 #else
  90 # define PREEMPT_DISABLE_OFFSET 0
  91 #endif
  92
  93 /*
  94  * The preempt_count offset needed for things like:
  95  *
  96  *  spin_lock_bh()
  97  *
  98  * Which need to disable both preemption (CONFIG_PREEMPT_COUNT) and
  99  * softirqs, such that unlock sequences of:
 100  *
 101  *  spin_unlock();
 102  *  local_bh_enable();
 103  *
 104  * Work as expected.
 105  */
 106 #define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_DISABLE_OFFSET)
 107
 108 /*
 109  * Are we running in atomic context?  WARNING: this macro cannot
 110  * always detect atomic context; in particular, it cannot know about
 111  * held spinlocks in non-preemptible kernels.  Thus it should not be
 112  * used in the general case to determine whether sleeping is possible.
 113  * Do not use in_atomic() in driver code.
 114  */
 115 #define in_atomic()     (preempt_count() != 0)
 116
 117 /*
 118  * Check whether we were atomic before we did preempt_disable():
 119  * (used by the scheduler)
 120  */
 121 #define in_atomic_preempt_off() \
 122                 ((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_DISABLE_OFFSET)
 123
 124 #if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
 125 extern void preempt_count_add(int val);
 126 extern void preempt_count_sub(int val);
 127 #define preempt_count_dec_and_test() ({ preempt_count_sub(1); should_resched(); })
 128 #else
 129 #define preempt_count_add(val)  __preempt_count_add(val)
 130 #define preempt_count_sub(val)  __preempt_count_sub(val)
 131 #define preempt_count_dec_and_test() __preempt_count_dec_and_test()
 132 #endif
 133
 134 #define __preempt_count_inc() __preempt_count_add(1)
 135 #define __preempt_count_dec() __preempt_count_sub(1)
 136
 137 #define preempt_count_inc() preempt_count_add(1)
 138 #define preempt_count_dec() preempt_count_sub(1)
 139
 140 #define preempt_active_enter() \
 141 do { \
 142         preempt_count_add(PREEMPT_ACTIVE + PREEMPT_DISABLE_OFFSET); \
 143         barrier(); \
 144 } while (0)
 145
 146 #define preempt_active_exit() \
 147 do { \
 148         barrier(); \
 149         preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_DISABLE_OFFSET); \
 150 } while (0)
 151
 152 #ifdef CONFIG_PREEMPT_COUNT
 153
 154 #define preempt_disable() \
 155 do { \
 156         preempt_count_inc(); \
 157         barrier(); \
 158 } while (0)
 159
 160 #define sched_preempt_enable_no_resched() \
 161 do { \
 162         barrier(); \
 163         preempt_count_dec(); \
 164 } while (0)
 165
 166 #define preempt_enable_no_resched() sched_preempt_enable_no_resched()
 167
 168 #define preemptible()   (preempt_count() == 0 && !irqs_disabled())
 169
 170 #ifdef CONFIG_PREEMPT
 171 #define preempt_enable() \
 172 do { \
 173         barrier(); \
 174         if (unlikely(preempt_count_dec_and_test())) \
 175                 __preempt_schedule(); \
 176 } while (0)
 177
 178 #define preempt_enable_notrace() \
 179 do { \
 180         barrier(); \
 181         if (unlikely(__preempt_count_dec_and_test())) \
 182                 __preempt_schedule_notrace(); \
 183 } while (0)
 184
 185 #define preempt_check_resched() \
 186 do { \
 187         if (should_resched()) \
 188                 __preempt_schedule(); \
 189 } while (0)
 190
 191 #else /* !CONFIG_PREEMPT */
 192 #define preempt_enable() \
 193 do { \
 194         barrier(); \
 195         preempt_count_dec(); \
 196 } while (0)
 197
 198 #define preempt_enable_notrace() \
 199 do { \
 200         barrier(); \
 201         __preempt_count_dec(); \
 202 } while (0)
 203
 204 #define preempt_check_resched() do { } while (0)
 205 #endif /* CONFIG_PREEMPT */
 206
 207 #define preempt_disable_notrace() \
 208 do { \
 209         __preempt_count_inc(); \
 210         barrier(); \
 211 } while (0)
 212
 213 #define preempt_enable_no_resched_notrace() \
 214 do { \
 215         barrier(); \
 216         __preempt_count_dec(); \
 217 } while (0)
 218
 219 #else /* !CONFIG_PREEMPT_COUNT */
 220
 221 /*
 222  * Even if we don't have any preemption, we need preempt disable/enable
 223  * to be barriers, so that we don't have things like get_user/put_user
 224  * that can cause faults and scheduling migrate into our preempt-protected
 225  * region.
 226  */
 227 #define preempt_disable()                       barrier()
 228 #define sched_preempt_enable_no_resched()       barrier()
 229 #define preempt_enable_no_resched()             barrier()
 230 #define preempt_enable()                        barrier()
 231 #define preempt_check_resched()                 do { } while (0)
 232
 233 #define preempt_disable_notrace()               barrier()
 234 #define preempt_enable_no_resched_notrace()     barrier()
 235 #define preempt_enable_notrace()                barrier()
 236 #define preemptible()                           0
 237
 238 #endif /* CONFIG_PREEMPT_COUNT */
 239
 240 #ifdef MODULE
 241 /*
 242  * Modules have no business playing preemption tricks.
 243  */
 244 #undef sched_preempt_enable_no_resched
 245 #undef preempt_enable_no_resched
 246 #undef preempt_enable_no_resched_notrace
 247 #undef preempt_check_resched
 248 #endif
 249
 250 #define preempt_set_need_resched() \
 251 do { \
 252         set_preempt_need_resched(); \
 253 } while (0)
 254 #define preempt_fold_need_resched() \
 255 do { \
 256         if (tif_need_resched()) \
 257                 set_preempt_need_resched(); \
 258 } while (0)
 259
 260 #ifdef CONFIG_PREEMPT_NOTIFIERS
 261
 262 struct preempt_notifier;
 263
 264 /**
 265  * preempt_ops - notifiers called when a task is preempted and rescheduled
 266  * @sched_in: we're about to be rescheduled:
 267  *    notifier: struct preempt_notifier for the task being scheduled
 268  *    cpu:  cpu we're scheduled on
 269  * @sched_out: we've just been preempted
 270  *    notifier: struct preempt_notifier for the task being preempted
 271  *    next: the task that's kicking us out
 272  *
 273  * Please note that sched_in and out are called under different
 274  * contexts.  sched_out is called with rq lock held and irq disabled
 275  * while sched_in is called without rq lock and irq enabled.  This
 276  * difference is intentional and depended upon by its users.
 277  */
 278 struct preempt_ops {
 279         void (*sched_in)(struct preempt_notifier *notifier, int cpu);
 280         void (*sched_out)(struct preempt_notifier *notifier,
 281                           struct task_struct *next);
 282 };
 283
 284 /**
 285  * preempt_notifier - key for installing preemption notifiers
 286  * @link: internal use
 287  * @ops: defines the notifier functions to be called
 288  *
 289  * Usually used in conjunction with container_of().
 290  */
 291 struct preempt_notifier {
 292         struct hlist_node link;
 293         struct preempt_ops *ops;
 294 };
 295
 296 void preempt_notifier_register(struct preempt_notifier *notifier);
 297 void preempt_notifier_unregister(struct preempt_notifier *notifier);
 298
 299 static inline void preempt_notifier_init(struct preempt_notifier *notifier,
 300                                      struct preempt_ops *ops)
 301 {
 302         INIT_HLIST_NODE(&notifier->link);
 303         notifier->ops = ops;
 304 }
 305
 306 #endif
 307
 308 #endif /* __LINUX_PREEMPT_H */