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 use the MSB mostly because its available; see <linux/preempt_mask.h> for
  14  * the other bits -- can't include that header due to inclusion hell.
  15  */
  16 #define PREEMPT_NEED_RESCHED    0x80000000
  17
  18 #include <asm/preempt.h>
  19
  20 /*
  21  * We put the hardirq and softirq counter into the preemption
  22  * counter. The bitmask has the following meaning:
  23  *
  24  * - bits 0-7 are the preemption count (max preemption depth: 256)
  25  * - bits 8-15 are the softirq count (max # of softirqs: 256)
  26  *
  27  * The hardirq count could in theory be the same as the number of
  28  * interrupts in the system, but we run all interrupt handlers with
  29  * interrupts disabled, so we cannot have nesting interrupts. Though
  30  * there are a few palaeontologic drivers which reenable interrupts in
  31  * the handler, so we need more than one bit here.
  32  *
  33  * PREEMPT_MASK:        0x000000ff
  34  * SOFTIRQ_MASK:        0x0000ff00
  35  * HARDIRQ_MASK:        0x000f0000
  36  *     NMI_MASK:        0x00100000
  37  * PREEMPT_ACTIVE:      0x00200000
  38  */
  39 #define PREEMPT_BITS    8
  40 #define SOFTIRQ_BITS    8
  41 #define HARDIRQ_BITS    4
  42 #define NMI_BITS        1
  43
  44 #define PREEMPT_SHIFT   0
  45 #define SOFTIRQ_SHIFT   (PREEMPT_SHIFT + PREEMPT_BITS)
  46 #define HARDIRQ_SHIFT   (SOFTIRQ_SHIFT + SOFTIRQ_BITS)
  47 #define NMI_SHIFT       (HARDIRQ_SHIFT + HARDIRQ_BITS)
  48
  49 #define __IRQ_MASK(x)   ((1UL << (x))-1)
  50
  51 #define PREEMPT_MASK    (__IRQ_MASK(PREEMPT_BITS) << PREEMPT_SHIFT)
  52 #define SOFTIRQ_MASK    (__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)
  53 #define HARDIRQ_MASK    (__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)
  54 #define NMI_MASK        (__IRQ_MASK(NMI_BITS)     << NMI_SHIFT)
  55
  56 #define PREEMPT_OFFSET  (1UL << PREEMPT_SHIFT)
  57 #define SOFTIRQ_OFFSET  (1UL << SOFTIRQ_SHIFT)
  58 #define HARDIRQ_OFFSET  (1UL << HARDIRQ_SHIFT)
  59 #define NMI_OFFSET      (1UL << NMI_SHIFT)
  60
  61 #define SOFTIRQ_DISABLE_OFFSET  (2 * SOFTIRQ_OFFSET)
  62
  63 #define PREEMPT_ACTIVE_BITS     1
  64 #define PREEMPT_ACTIVE_SHIFT    (NMI_SHIFT + NMI_BITS)
  65 #define PREEMPT_ACTIVE  (__IRQ_MASK(PREEMPT_ACTIVE_BITS) << PREEMPT_ACTIVE_SHIFT)
  66
  67 #define hardirq_count() (preempt_count() & HARDIRQ_MASK)
  68 #define softirq_count() (preempt_count() & SOFTIRQ_MASK)
  69 #define irq_count()     (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK \
  70                                  | NMI_MASK))
  71
  72 /*
  73  * Are we doing bottom half or hardware interrupt processing?
  74  * Are we in a softirq context? Interrupt context?
  75  * in_softirq - Are we currently processing softirq or have bh disabled?
  76  * in_serving_softirq - Are we currently processing softirq?
  77  */
  78 #define in_irq()                (hardirq_count())
  79 #define in_softirq()            (softirq_count())
  80 #define in_interrupt()          (irq_count())
  81 #define in_serving_softirq()    (softirq_count() & SOFTIRQ_OFFSET)
  82
  83 /*
  84  * Are we in NMI context?
  85  */
  86 #define in_nmi()        (preempt_count() & NMI_MASK)
  87
  88 #if defined(CONFIG_PREEMPT_COUNT)
  89 # define PREEMPT_CHECK_OFFSET 1
  90 #else
  91 # define PREEMPT_CHECK_OFFSET 0
  92 #endif
  93
  94 /*
  95  * The preempt_count offset needed for things like:
  96  *
  97  *  spin_lock_bh()
  98  *
  99  * Which need to disable both preemption (CONFIG_PREEMPT_COUNT) and
 100  * softirqs, such that unlock sequences of:
 101  *
 102  *  spin_unlock();
 103  *  local_bh_enable();
 104  *
 105  * Work as expected.
 106  */
 107 #define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_CHECK_OFFSET)
 108
 109 /*
 110  * Are we running in atomic context?  WARNING: this macro cannot
 111  * always detect atomic context; in particular, it cannot know about
 112  * held spinlocks in non-preemptible kernels.  Thus it should not be
 113  * used in the general case to determine whether sleeping is possible.
 114  * Do not use in_atomic() in driver code.
 115  */
 116 #define in_atomic()     ((preempt_count() & ~PREEMPT_ACTIVE) != 0)
 117
 118 /*
 119  * Check whether we were atomic before we did preempt_disable():
 120  * (used by the scheduler, *after* releasing the kernel lock)
 121  */
 122 #define in_atomic_preempt_off() \
 123                 ((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_CHECK_OFFSET)
 124
 125 #ifdef CONFIG_PREEMPT_COUNT
 126 # define preemptible()  (preempt_count() == 0 && !irqs_disabled())
 127 #else
 128 # define preemptible()  0
 129 #endif
 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() ({ preempt_count_sub(1); should_resched(); })
 135 #else
 136 #define preempt_count_add(val)  __preempt_count_add(val)
 137 #define preempt_count_sub(val)  __preempt_count_sub(val)
 138 #define preempt_count_dec_and_test() __preempt_count_dec_and_test()
 139 #endif
 140
 141 #define __preempt_count_inc() __preempt_count_add(1)
 142 #define __preempt_count_dec() __preempt_count_sub(1)
 143
 144 #define preempt_count_inc() preempt_count_add(1)
 145 #define preempt_count_dec() preempt_count_sub(1)
 146
 147 #ifdef CONFIG_PREEMPT_COUNT
 148
 149 #define preempt_disable() \
 150 do { \
 151         preempt_count_inc(); \
 152         barrier(); \
 153 } while (0)
 154
 155 #define sched_preempt_enable_no_resched() \
 156 do { \
 157         barrier(); \
 158         preempt_count_dec(); \
 159 } while (0)
 160
 161 #define preempt_enable_no_resched() sched_preempt_enable_no_resched()
 162
 163 #ifdef CONFIG_PREEMPT
 164 #define preempt_enable() \
 165 do { \
 166         barrier(); \
 167         if (unlikely(preempt_count_dec_and_test())) \
 168                 __preempt_schedule(); \
 169 } while (0)
 170
 171 #define preempt_check_resched() \
 172 do { \
 173         if (should_resched()) \
 174                 __preempt_schedule(); \
 175 } while (0)
 176
 177 #else
 178 #define preempt_enable() \
 179 do { \
 180         barrier(); \
 181         preempt_count_dec(); \
 182 } while (0)
 183 #define preempt_check_resched() do { } while (0)
 184 #endif
 185
 186 #define preempt_disable_notrace() \
 187 do { \
 188         __preempt_count_inc(); \
 189         barrier(); \
 190 } while (0)
 191
 192 #define preempt_enable_no_resched_notrace() \
 193 do { \
 194         barrier(); \
 195         __preempt_count_dec(); \
 196 } while (0)
 197
 198 #ifdef CONFIG_PREEMPT
 199
 200 #ifndef CONFIG_CONTEXT_TRACKING
 201 #define __preempt_schedule_context() __preempt_schedule()
 202 #endif
 203
 204 #define preempt_enable_notrace() \
 205 do { \
 206         barrier(); \
 207         if (unlikely(__preempt_count_dec_and_test())) \
 208                 __preempt_schedule_context(); \
 209 } while (0)
 210 #else
 211 #define preempt_enable_notrace() \
 212 do { \
 213         barrier(); \
 214         __preempt_count_dec(); \
 215 } while (0)
 216 #endif
 217
 218 #else /* !CONFIG_PREEMPT_COUNT */
 219
 220 /*
 221  * Even if we don't have any preemption, we need preempt disable/enable
 222  * to be barriers, so that we don't have things like get_user/put_user
 223  * that can cause faults and scheduling migrate into our preempt-protected
 224  * region.
 225  */
 226 #define preempt_disable()                       barrier()
 227 #define sched_preempt_enable_no_resched()       barrier()
 228 #define preempt_enable_no_resched()             barrier()
 229 #define preempt_enable()                        barrier()
 230 #define preempt_check_resched()                 do { } while (0)
 231
 232 #define preempt_disable_notrace()               barrier()
 233 #define preempt_enable_no_resched_notrace()     barrier()
 234 #define preempt_enable_notrace()                barrier()
 235
 236 #endif /* CONFIG_PREEMPT_COUNT */
 237
 238 #ifdef MODULE
 239 /*
 240  * Modules have no business playing preemption tricks.
 241  */
 242 #undef sched_preempt_enable_no_resched
 243 #undef preempt_enable_no_resched
 244 #undef preempt_enable_no_resched_notrace
 245 #undef preempt_check_resched
 246 #endif
 247
 248 #define preempt_set_need_resched() \
 249 do { \
 250         set_preempt_need_resched(); \
 251 } while (0)
 252 #define preempt_fold_need_resched() \
 253 do { \
 254         if (tif_need_resched()) \
 255                 set_preempt_need_resched(); \
 256 } while (0)
 257
 258 #ifdef CONFIG_PREEMPT_NOTIFIERS
 259
 260 struct preempt_notifier;
 261
 262 /**
 263  * preempt_ops - notifiers called when a task is preempted and rescheduled
 264  * @sched_in: we're about to be rescheduled:
 265  *    notifier: struct preempt_notifier for the task being scheduled
 266  *    cpu:  cpu we're scheduled on
 267  * @sched_out: we've just been preempted
 268  *    notifier: struct preempt_notifier for the task being preempted
 269  *    next: the task that's kicking us out
 270  *
 271  * Please note that sched_in and out are called under different
 272  * contexts.  sched_out is called with rq lock held and irq disabled
 273  * while sched_in is called without rq lock and irq enabled.  This
 274  * difference is intentional and depended upon by its users.
 275  */
 276 struct preempt_ops {
 277         void (*sched_in)(struct preempt_notifier *notifier, int cpu);
 278         void (*sched_out)(struct preempt_notifier *notifier,
 279                           struct task_struct *next);
 280 };
 281
 282 /**
 283  * preempt_notifier - key for installing preemption notifiers
 284  * @link: internal use
 285  * @ops: defines the notifier functions to be called
 286  *
 287  * Usually used in conjunction with container_of().
 288  */
 289 struct preempt_notifier {
 290         struct hlist_node link;
 291         struct preempt_ops *ops;
 292 };
 293
 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 */