tools/include: Remove ACCESS_ONCE()
There are no longer any usersapce uses of ACCESS_ONCE(), so we can remove the definition from our userspace <linux/compiler.h>, which is only used by tools in the kernel directory (i.e. it isn't a uapi header). This patch removes the ACCESS_ONCE() definition, and updates comments which referred to it. At the same time, some inconsistent and redundant whitespace is removed from comments. Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Joe Perches <joe@perches.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: apw@canonical.com Link: http://lkml.kernel.org/r/20171127103824.36526-3-mark.rutland@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -84,8 +84,6 @@
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#define uninitialized_var(x) x = *(&(x))
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#define uninitialized_var(x) x = *(&(x))
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#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
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#include <linux/types.h>
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#include <linux/types.h>
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/*
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/*
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@ -135,20 +133,19 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
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/*
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/*
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* Prevent the compiler from merging or refetching reads or writes. The
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* Prevent the compiler from merging or refetching reads or writes. The
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* compiler is also forbidden from reordering successive instances of
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* compiler is also forbidden from reordering successive instances of
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* READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), but only when the
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* READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
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* compiler is aware of some particular ordering. One way to make the
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* particular ordering. One way to make the compiler aware of ordering is to
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* compiler aware of ordering is to put the two invocations of READ_ONCE,
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* put the two invocations of READ_ONCE or WRITE_ONCE in different C
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* WRITE_ONCE or ACCESS_ONCE() in different C statements.
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* statements.
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*
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*
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* In contrast to ACCESS_ONCE these two macros will also work on aggregate
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* These two macros will also work on aggregate data types like structs or
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* data types like structs or unions. If the size of the accessed data
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* unions. If the size of the accessed data type exceeds the word size of
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* type exceeds the word size of the machine (e.g., 32 bits or 64 bits)
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* the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
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* READ_ONCE() and WRITE_ONCE() will fall back to memcpy and print a
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* fall back to memcpy and print a compile-time warning.
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* compile-time warning.
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*
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*
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* Their two major use cases are: (1) Mediating communication between
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* Their two major use cases are: (1) Mediating communication between
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* process-level code and irq/NMI handlers, all running on the same CPU,
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* process-level code and irq/NMI handlers, all running on the same CPU,
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* and (2) Ensuring that the compiler does not fold, spindle, or otherwise
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* and (2) Ensuring that the compiler does not fold, spindle, or otherwise
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* mutilate accesses that either do not require ordering or that interact
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* mutilate accesses that either do not require ordering or that interact
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* with an explicit memory barrier or atomic instruction that provides the
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* with an explicit memory barrier or atomic instruction that provides the
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* required ordering.
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* required ordering.
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