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         extern __PCPU_ATTRS(sec) __typeof__(type) name;                 \
  73         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES __weak                 \
  74         __typeof__(type) name
  75 #else
  76 /*
  77  * Normal declaration and definition macros.
  78  */
  79 #define DECLARE_PER_CPU_SECTION(type, name, sec)                        \
  80         extern __PCPU_ATTRS(sec) __typeof__(type) name
  81
  82 #define DEFINE_PER_CPU_SECTION(type, name, sec)                         \
  83         __PCPU_ATTRS(sec) PER_CPU_DEF_ATTRIBUTES                        \
  84         __typeof__(type) name
  85 #endif
  86
  87 /*
  88  * Variant on the per-CPU variable declaration/definition theme used for
  89  * ordinary per-CPU variables.
  90  */
  91 #define DECLARE_PER_CPU(type, name)                                     \
  92         DECLARE_PER_CPU_SECTION(type, name, "")
  93
  94 #define DEFINE_PER_CPU(type, name)                                      \
  95         DEFINE_PER_CPU_SECTION(type, name, "")
  96
  97 /*
  98  * Declaration/definition used for per-CPU variables that must come first in
  99  * the set of variables.
 100  */
 101 #define DECLARE_PER_CPU_FIRST(type, name)                               \
 102         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
 103
 104 #define DEFINE_PER_CPU_FIRST(type, name)                                \
 105         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_FIRST_SECTION)
 106
 107 /*
 108  * Declaration/definition used for per-CPU variables that must be cacheline
 109  * aligned under SMP conditions so that, whilst a particular instance of the
 110  * data corresponds to a particular CPU, inefficiencies due to direct access by
 111  * other CPUs are reduced by preventing the data from unnecessarily spanning
 112  * cachelines.
 113  *
 114  * An example of this would be statistical data, where each CPU's set of data
 115  * is updated by that CPU alone, but the data from across all CPUs is collated
 116  * by a CPU processing a read from a proc file.
 117  */
 118 #define DECLARE_PER_CPU_SHARED_ALIGNED(type, name)                      \
 119         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 120         ____cacheline_aligned_in_smp
 121
 122 #define DEFINE_PER_CPU_SHARED_ALIGNED(type, name)                       \
 123         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_SHARED_ALIGNED_SECTION) \
 124         ____cacheline_aligned_in_smp
 125
 126 #define DECLARE_PER_CPU_ALIGNED(type, name)                             \
 127         DECLARE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)    \
 128         ____cacheline_aligned
 129
 130 #define DEFINE_PER_CPU_ALIGNED(type, name)                              \
 131         DEFINE_PER_CPU_SECTION(type, name, PER_CPU_ALIGNED_SECTION)     \
 132         ____cacheline_aligned
 133
 134 /*
 135  * Declaration/definition used for per-CPU variables that must be page aligned.
 136  */
 137 #define DECLARE_PER_CPU_PAGE_ALIGNED(type, name)                        \
 138         DECLARE_PER_CPU_SECTION(type, name, "..page_aligned")           \
 139         __aligned(PAGE_SIZE)
 140
 141 #define DEFINE_PER_CPU_PAGE_ALIGNED(type, name)                         \
 142         DEFINE_PER_CPU_SECTION(type, name, "..page_aligned")            \
 143         __aligned(PAGE_SIZE)
 144
 145 /*
 146  * Declaration/definition used for per-CPU variables that must be read mostly.
 147  */
 148 #define DECLARE_PER_CPU_READ_MOSTLY(type, name)                 \
 149         DECLARE_PER_CPU_SECTION(type, name, "..readmostly")
 150
 151 #define DEFINE_PER_CPU_READ_MOSTLY(type, name)                          \
 152         DEFINE_PER_CPU_SECTION(type, name, "..readmostly")
 153
 154 /*
 155  * Intermodule exports for per-CPU variables.  sparse forgets about
 156  * address space across EXPORT_SYMBOL(), change EXPORT_SYMBOL() to
 157  * noop if __CHECKER__.
 158  */
 159 #ifndef __CHECKER__
 160 #define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(var)
 161 #define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(var)
 162 #else
 163 #define EXPORT_PER_CPU_SYMBOL(var)
 164 #define EXPORT_PER_CPU_SYMBOL_GPL(var)
 165 #endif
 166
 167 #endif /* _LINUX_PERCPU_DEFS_H */