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The atomic64_add_unless function compares an atomic variable with a given value and, if they are not equal, adds another given value to the atomic variable. The function returns zero if the addition did not occur and non-zero otherwise. On ARM, the return value is initialised to 1 in C code. Inline assembly code then performs the atomic64_add_unless operation, setting the return value to 0 iff the addition does not occur. This means that when the addition *does* occur, the value of ret must be preserved across the inline assembly and therefore requires a "+r" constraint rather than the current one of "=&r". Thanks to Nicolas Pitre for helping to spot this. Cc: stable@kernel.org Reviewed-by: Nicolas Pitre <nicolas.pitre@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> |
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