include/linux/percpu-defs.h

   1 #ifndef _LINUX_PERCPU_DEFS_H
   2 #define _LINUX_PERCPU_DEFS_H
   3
   4 /*
   5  * Base implementations of per-CPU variable declarations and definitions, where
   6  * the section in which the variable is to be placed is provided by the
   7  * 'sec' argument.  This may be used to affect the parameters governing the
   8  * variable's storage.
   9  *
  10  * NOTE!  The sections for the DECLARE and for the DEFINE must match, lest
  11  * linkage errors occur due the compiler generating the wrong code to access
  12  * that section.
  13  */
  14 #define __PCPU_ATTRS(sec)                                               \
  15         __percpu __attribute__((section(PER_CPU_BASE_SECTION sec)))     \
  16         PER_CPU_ATTRIBUTES
  17
  18 #define __PCPU_DUMMY_ATTRS                                              \
  19         __attribute__((section(".discard"), unused))
  20
  21 /*
  22  * Macro which verifies @ptr is a percpu pointer without evaluating
  23  * @ptr.  This is to be used in percpu accessors to verify that the
  24  * input parameter is a percpu pointer.
  25  *
  26  * + 0 is required in order to convert the pointer type from a
  27  * potential array type to a pointer to a single item of the array.
  28  */
  29 #define __verify_pcpu_ptr(ptr)  do {                                    \
  30         const void __percpu *__vpp_verify = (typeof((ptr) + 0))NULL;    \
  31         (void)__vpp_verify;                                             \
  32 } while (0)
  33
  34 /*
  35  * s390 and alpha modules require percpu variables to be defined as
  36  * weak to force the compiler to generate GOT based external
  37  * references for them.  This is necessary because percpu sections
  38  * will be located outside of the usually addressable area.
  39  *
  40  * This definition puts the following two extra restrictions when
  41  * defining percpu variables.
  42  *
  43  * 1. The symbol must be globally unique, even the static ones.
  44  * 2. Static percpu variables cannot be defined inside a function.
  45  *
  46  * Archs which need weak percpu definitions should define
  47  * ARCH_NEEDS_WEAK_PER_CPU in asm/percpu.h when necessary.
  48  *
  49  * To ensure that the generic code observes the above two
  50  * restrictions, if CONFIG_DEBUG_FORCE_WEAK_PER_CPU is set weak
  51  * definition is used for all cases.
  52  */
  53 #if defined(ARCH_NEEDS_WEAK_PER_CPU) || defined(CONFIG_DEBUG_FORCE_WEAK_PER_CPU)
  54 /*
  55  * __pcpu_scope_* dummy variable is used to enforce scope.  It
  56  * receives the static modifier when it's used in front of
  57  * DEFINE_PER_CPU() and will trigger build failure if
  58  * DECLARE_PER_CPU() is used for the same variable.
  59  *
  60  * __pcpu_unique_* dummy variable is used to enforce symbol uniqueness
  61  * such that hidden weak symbol collision, which will cause unrelated
  62  * variables to share the same address, can be detected during build.
  63  */
  64 #define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  65         extern __PCPU_DUMMY_ATTRS char __pcpu_scope_##name;             \
  66         extern __PCPU_ATTRS(sec) __typeof__(type) name
  67
  68 #define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  69         __PCPU_DUMMY_ATTRS char __pcpu_scope_##name;                    \
  70         extern __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;            \
  71         __PCPU_DUMMY_ATTRS char __pcpu_unique_##name;                   \
  72         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES __weak                 \
  73         __typeof__(type) name
  74 #else
  75 /*
  76  * Normal declaration and definition macros.
  77  */
  78 #define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  79         extern __PCPU_ATTRS(sec) __typeof__(type) name
  80
  81 #define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  82         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES                        \
  83         __typeof__(type) name
  84 #endif
  85
  86 /*
  87  * Variant on the per-CPU variable declaration/definition theme used for
  88  * ordinary per-CPU variables.
  89  */
  90 #define DECLARE_PER_CPU(type, name)                                     \
  91         DECLARE_PER_CPU_SECTION(type, name, "")
  92
  93 #define DEFINE_PER_CPU(type, name)                                      \
  94         DEFINE_PER_CPU_SECTION(type, name, "")
  95
  96 /*
  97  * Declaration/definition used for per-CPU variables that must come first in
  98  * the set of variables.
  99  */
 100 #define DECLARE_PER_CPU_FIRST(type, name)                               \
 101         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
 102
 103 #define DEFINE_PER_CPU_FIRST(type, name)                                \
 104         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
 105
 106 /*
 107  * Declaration/definition used for per-CPU variables that must be cacheline
 108  * aligned under SMP conditions so that, whilst a particular instance of the
 109  * data corresponds to a particular CPU, inefficiencies due to direct access by
 110  * other CPUs are reduced by preventing the data from unnecessarily spanning
 111  * cachelines.
 112  *
 113  * An example of this would be statistical data, where each CPU's set of data
 114  * is updated by that CPU alone, but the data from across all CPUs is collated
 115  * by a CPU processing a read from a proc file.
 116  */
 117 #define DECLARE_PER_CPU_SHARED_ALIGNED(type, name)                      \
 118         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 119         ____cacheline_aligned_in_smp
 120
 121 #define DEFINE_PER_CPU_SHARED_ALIGNED(type, name)                       \
 122         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 123         ____cacheline_aligned_in_smp
 124
 125 #define DECLARE_PER_CPU_ALIGNED(type, name)                             \
 126         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)    \
 127         ____cacheline_aligned
 128
 129 #define DEFINE_PER_CPU_ALIGNED(type, name)                              \
 130         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)     \
 131         ____cacheline_aligned
 132
 133 /*
 134  * Declaration/definition used for per-CPU variables that must be page aligned.
 135  */
 136 #define DECLARE_PER_CPU_PAGE_ALIGNED(type, name)                        \
 137         DECLARE_PER_CPU_SECTION(type, name, "..page_aligned")           \
 138         __aligned(PAGE_SIZE)
 139
 140 #define DEFINE_PER_CPU_PAGE_ALIGNED(type, name)                         \
 141         DEFINE_PER_CPU_SECTION(type, name, "..page_aligned")            \
 142         __aligned(PAGE_SIZE)
 143
 144 /*
 145  * Declaration/definition used for per-CPU variables that must be read mostly.
 146  */
 147 #define DECLARE_PER_CPU_READ_MOSTLY(type, name)                 \
 148         DECLARE_PER_CPU_SECTION(type, name, "..readmostly")
 149
 150 #define DEFINE_PER_CPU_READ_MOSTLY(type, name)                          \
 151         DEFINE_PER_CPU_SECTION(type, name, "..readmostly")
 152
 153 /*
 154  * Intermodule exports for per-CPU variables.  sparse forgets about
 155  * address space across EXPORT_SYMBOL(), change EXPORT_SYMBOL() to
 156  * noop if __CHECKER__.
 157  */
 158 #ifndef __CHECKER__
 159 #define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(var)
 160 #define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(var)
 161 #else
 162 #define EXPORT_PER_CPU_SYMBOL(var)
 163 #define EXPORT_PER_CPU_SYMBOL_GPL(var)
 164 #endif
 165
 166 #endif /* _LINUX_PERCPU_DEFS_H */