diff options
| -rw-r--r-- | include/linux/cnt32_to_63.h | 22 |
1 files changed, 16 insertions, 6 deletions
diff --git a/include/linux/cnt32_to_63.h b/include/linux/cnt32_to_63.h index 8c0f9505b48..7605fdd1eb6 100644 --- a/include/linux/cnt32_to_63.h +++ b/include/linux/cnt32_to_63.h @@ -16,6 +16,7 @@ #include <linux/compiler.h> #include <linux/types.h> #include <asm/byteorder.h> +#include <asm/system.h> /* this is used only to give gcc a clue about good code generation */ union cnt32_to_63 { @@ -53,11 +54,19 @@ union cnt32_to_63 { * needed increment. And any race in updating the value in memory is harmless * as the same value would simply be stored more than once. * - * The only restriction for the algorithm to work properly is that this - * code must be executed at least once per each half period of the 32-bit - * counter to properly update the state bit in memory. This is usually not a - * problem in practice, but if it is then a kernel timer could be scheduled - * to manage for this code to be executed often enough. + * The restrictions for the algorithm to work properly are: + * + * 1) this code must be called at least once per each half period of the + * 32-bit counter; + * + * 2) this code must not be preempted for a duration longer than the + * 32-bit counter half period minus the longest period between two + * calls to this code. + * + * Those requirements ensure proper update to the state bit in memory. + * This is usually not a problem in practice, but if it is then a kernel + * timer should be scheduled to manage for this code to be executed often + * enough. * * Note that the top bit (bit 63) in the returned value should be considered * as garbage. It is not cleared here because callers are likely to use a @@ -68,9 +77,10 @@ union cnt32_to_63 { */ #define cnt32_to_63(cnt_lo) \ ({ \ - static volatile u32 __m_cnt_hi; \ + static u32 __m_cnt_hi; \ union cnt32_to_63 __x; \ __x.hi = __m_cnt_hi; \ + smp_rmb(); \ __x.lo = (cnt_lo); \ if (unlikely((s32)(__x.hi ^ __x.lo) < 0)) \ __m_cnt_hi = __x.hi = (__x.hi ^ 0x80000000) + (__x.hi >> 31); \ |