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READ_ONCE: Fix comment describing 2x32-bit atomicity

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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>
This commit is contained in:
Will Deacon 2020-05-11 21:59:51 +01:00
parent 10415533a9
commit 5872f1a2e5
1 changed files with 3 additions and 3 deletions
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6
include/linux/compiler.h
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@ -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 * 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 * actually be atomic in some cases (namely Armv7 + LPAE), but for others we
* the access being split into 2x32-bit accesses for a 32-bit quantity (e.g. * rely on the access being split into 2x32-bit accesses for a 32-bit quantity
* a virtual address) and a strong prevailing wind. * (e.g. a virtual address) and a strong prevailing wind.
*/ */
#define compiletime_assert_rwonce_type(t) \ #define compiletime_assert_rwonce_type(t) \
compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \ compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \