Commit 5872f1a2 authored May 11, 2020 by Will Deacon

READ_ONCE: Fix comment describing 2x32-bit atomicity



READ_ONCE() permits 64-bit accesses on 32-bit architectures, since this
crops up in a few places and is generally harmless because either the
upper bits are always zero (e.g. for a virtual address or 32-bit time_t)
or the architecture provides 64-bit atomicity anyway.

Update the corresponding comment above compiletime_assert_rwonce_type(),
which incorrectly states that 32-bit x86 provides 64-bit atomicity, and
instead reference 32-bit Armv7 with LPAE.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Will Deacon <will@kernel.org>

parent 10415533

include/linux/compiler.h

+3 −3

Original line number	Diff line number	Diff line
		@@ -332,9 +332,9 @@ static inline void offset_to_ptr(const int off)

		/*
		* Yes, this permits 64-bit accesses on 32-bit architectures. These will
		* actually be atomic in many cases (namely x86), 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.
		* 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), \

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