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Merge branch 'rwonce/rework' of git://git.kernel.org/pub/scm/linux/kernel/git/will/linux

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Pull READ/WRITE_ONCE rework from Will Deacon:
 "This the READ_ONCE rework I've been working on for a while, which
  bumps the minimum GCC version and improves code-gen on arm64 when
  stack protector is enabled"

[ Side note: I'm _really_ tempted to raise the minimum gcc version to
  4.9, so that we can just say that we require _Generic() support.

  That would allow us to more cleanly handle a lot of the cases where we
  depend on very complex macros with 'sizeof' or __builtin_choose_expr()
  with __builtin_types_compatible_p() etc.

  This branch has a workaround for sparse not handling _Generic(),
  either, but that was already fixed in the sparse development branch,
  so it's really just gcc-4.9 that we'd require.   - Linus ]

* 'rwonce/rework' of git://git.kernel.org/pub/scm/linux/kernel/git/will/linux:
  compiler_types.h: Use unoptimized __unqual_scalar_typeof for sparse
  compiler_types.h: Optimize __unqual_scalar_typeof compilation time
  compiler.h: Enforce that READ_ONCE_NOCHECK() access size is sizeof(long)
  compiler-types.h: Include naked type in __pick_integer_type() match
  READ_ONCE: Fix comment describing 2x32-bit atomicity
  gcov: Remove old GCC 3.4 support
  arm64: barrier: Use '__unqual_scalar_typeof' for acquire/release macros
  locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros
  READ_ONCE: Drop pointer qualifiers when reading from scalar types
  READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses
  READ_ONCE: Simplify implementations of {READ,WRITE}_ONCE()
  arm64: csum: Disable KASAN for do_csum()
  fault_inject: Don't rely on "return value" from WRITE_ONCE()
  net: tls: Avoid assigning 'const' pointer to non-const pointer
  netfilter: Avoid assigning 'const' pointer to non-const pointer
  compiler/gcc: Raise minimum GCC version for kernel builds to 4.8
This commit is contained in:
Linus Torvalds 2020-06-10 14:46:54 -07:00
commit 4152d146ee
18 changed files with 161 additions and 719 deletions
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148
include/linux/compiler.h
View file

@ -230,60 +230,6 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
# define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
#endif
#include <uapi/linux/types.h>
#define __READ_ONCE_SIZE \
({ \
switch (size) { \
case 1: *(__u8 *)res = *(volatile __u8 *)p; break; \
case 2: *(__u16 *)res = *(volatile __u16 *)p; break; \
case 4: *(__u32 *)res = *(volatile __u32 *)p; break; \
case 8: *(__u64 *)res = *(volatile __u64 *)p; break; \
default: \
barrier(); \
__builtin_memcpy((void *)res, (const void *)p, size); \
barrier(); \
} \
})
static __always_inline
void __read_once_size(const volatile void *p, void *res, int size)
{
__READ_ONCE_SIZE;
}
#ifdef CONFIG_KASAN
/*
* We can't declare function 'inline' because __no_sanitize_address confilcts
* with inlining. Attempt to inline it may cause a build failure.
* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
* '__maybe_unused' allows us to avoid defined-but-not-used warnings.
*/
# define __no_kasan_or_inline __no_sanitize_address notrace __maybe_unused
#else
# define __no_kasan_or_inline __always_inline
#endif
static __no_kasan_or_inline
void __read_once_size_nocheck(const volatile void *p, void *res, int size)
{
__READ_ONCE_SIZE;
}
static __always_inline void __write_once_size(volatile void *p, void *res, int size)
{
switch (size) {
case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
case 4: *(volatile __u32 *)p = *(__u32 *)res; break;
case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
default:
barrier();
__builtin_memcpy((void *)p, (const void *)res, size);
barrier();
}
}
/*
* Prevent the compiler from merging or refetching reads or writes. The
* compiler is also forbidden from reordering successive instances of
@ -293,11 +239,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
* statements.
*
* These two macros will also work on aggregate data types like structs or
* unions. If the size of the accessed data type exceeds the word size of
* the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
* fall back to memcpy(). There's at least two memcpy()s: one for the
* __builtin_memcpy() and then one for the macro doing the copy of variable
* - '__u' allocated on the stack.
* unions.
*
* Their two major use cases are: (1) Mediating communication between
* process-level code and irq/NMI handlers, all running on the same CPU,
@ -309,23 +251,69 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
#include <asm/barrier.h>
#include <linux/kasan-checks.h>
#define __READ_ONCE(x, check) \
/*
* Use __READ_ONCE() instead of READ_ONCE() if you do not require any
* atomicity or dependency ordering guarantees. Note that this may result
* in tears!
*/
#define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x))
#define __READ_ONCE_SCALAR(x) \
({ \
union { typeof(x) __val; char __c[1]; } __u; \
if (check) \
__read_once_size(&(x), __u.__c, sizeof(x)); \
else \
__read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \
smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
__u.__val; \
__unqual_scalar_typeof(x) __x = __READ_ONCE(x); \
smp_read_barrier_depends(); \
(typeof(x))__x; \
})
#define READ_ONCE(x) __READ_ONCE(x, 1)
#define READ_ONCE(x) \
({ \
compiletime_assert_rwonce_type(x); \
__READ_ONCE_SCALAR(x); \
})
#define __WRITE_ONCE(x, val) \
do { \
*(volatile typeof(x) *)&(x) = (val); \
} while (0)
#define WRITE_ONCE(x, val) \
do { \
compiletime_assert_rwonce_type(x); \
__WRITE_ONCE(x, val); \
} while (0)
#ifdef CONFIG_KASAN
/*
* We can't declare function 'inline' because __no_sanitize_address conflicts
* with inlining. Attempt to inline it may cause a build failure.
* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
* '__maybe_unused' allows us to avoid defined-but-not-used warnings.
*/
# define __no_kasan_or_inline __no_sanitize_address notrace __maybe_unused
#else
# define __no_kasan_or_inline __always_inline
#endif
static __no_kasan_or_inline
unsigned long __read_once_word_nocheck(const void *addr)
{
return __READ_ONCE(*(unsigned long *)addr);
}
/*
* Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
* to hide memory access from KASAN.
* Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need to load a
* word from memory atomically but without telling KASAN. This is usually
* used by unwinding code when walking the stack of a running process.
*/
#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
#define READ_ONCE_NOCHECK(x) \
({ \
unsigned long __x; \
compiletime_assert(sizeof(x) == sizeof(__x), \
"Unsupported access size for READ_ONCE_NOCHECK()."); \
__x = __read_once_word_nocheck(&(x)); \
smp_read_barrier_depends(); \
(typeof(x))__x; \
})
static __no_kasan_or_inline
unsigned long read_word_at_a_time(const void *addr)
@ -334,14 +322,6 @@ unsigned long read_word_at_a_time(const void *addr)
return *(unsigned long *)addr;
}
#define WRITE_ONCE(x, val) \
({ \
union { typeof(x) __val; char __c[1]; } __u = \
{ .__val = (__force typeof(x)) (val) }; \
__write_once_size(&(x), __u.__c, sizeof(x)); \
__u.__val; \
})
#endif /* __KERNEL__ */
/*
@ -406,6 +386,16 @@ static inline void *offset_to_ptr(const int *off)
compiletime_assert(__native_word(t), \
"Need native word sized stores/loads for atomicity.")
/*
* Yes, this permits 64-bit accesses on 32-bit architectures. These will
* actually be atomic in some cases (namely Armv7 + LPAE), but for others we
* rely on the access being split into 2x32-bit accesses for a 32-bit quantity
* (e.g. a virtual address) and a strong prevailing wind.
*/
#define compiletime_assert_rwonce_type(t) \
compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \
"Unsupported access size for {READ,WRITE}_ONCE().")
/* &a[0] degrades to a pointer: a different type from an array */
#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))