diff --git a/arch/powerpc/include/asm/cputime.h b/arch/powerpc/include/asm/cputime.h index 607559ab271ff98b45de1f11964416bebaf32841..6c840ceab8201cc191f4699d15561c62b2e0c9c2 100644 --- a/arch/powerpc/include/asm/cputime.h +++ b/arch/powerpc/include/asm/cputime.h @@ -32,6 +32,8 @@ static inline void setup_cputime_one_jiffy(void) { } typedef u64 __nocast cputime_t; typedef u64 __nocast cputime64_t; +#define cmpxchg_cputime(ptr, old, new) cmpxchg(ptr, old, new) + #ifdef __KERNEL__ /* diff --git a/arch/s390/include/asm/cputime.h b/arch/s390/include/asm/cputime.h index f65bd36345194db88b71bca1f3740cca8744fa33..3001887f94b7a7c31ca01051db3f3cf9643e3ad0 100644 --- a/arch/s390/include/asm/cputime.h +++ b/arch/s390/include/asm/cputime.h @@ -18,6 +18,8 @@ typedef unsigned long long __nocast cputime_t; typedef unsigned long long __nocast cputime64_t; +#define cmpxchg_cputime(ptr, old, new) cmpxchg64(ptr, old, new) + static inline unsigned long __div(unsigned long long n, unsigned long base) { #ifndef CONFIG_64BIT diff --git a/include/asm-generic/cputime_jiffies.h b/include/asm-generic/cputime_jiffies.h index d5cb78f539861afdc82eae345ee4c8148fb2448e..fe386fc6e85e27f3c4a1b99262fe023db6a31fc3 100644 --- a/include/asm-generic/cputime_jiffies.h +++ b/include/asm-generic/cputime_jiffies.h @@ -3,6 +3,8 @@ typedef unsigned long __nocast cputime_t; +#define cmpxchg_cputime(ptr, old, new) cmpxchg(ptr, old, new) + #define cputime_one_jiffy jiffies_to_cputime(1) #define cputime_to_jiffies(__ct) (__force unsigned long)(__ct) #define cputime_to_scaled(__ct) (__ct) diff --git a/include/asm-generic/cputime_nsecs.h b/include/asm-generic/cputime_nsecs.h index 4e817606c5494126a31ae50e58a6e76242d89f07..0419485891f2a8eb6125f154f52d7b16c5fb05b4 100644 --- a/include/asm-generic/cputime_nsecs.h +++ b/include/asm-generic/cputime_nsecs.h @@ -21,6 +21,8 @@ typedef u64 __nocast cputime_t; typedef u64 __nocast cputime64_t; +#define cmpxchg_cputime(ptr, old, new) cmpxchg64(ptr, old, new) + #define cputime_one_jiffy jiffies_to_cputime(1) #define cputime_div(__ct, divisor) div_u64((__force u64)__ct, divisor) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 64492dff8a819fc56ac37c656ac6831c1209d58b..8394b1ee600c38ba6e9144a6326369b6ef0cdacd 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -554,6 +554,23 @@ static cputime_t scale_stime(u64 stime, u64 rtime, u64 total) return (__force cputime_t) scaled; } +/* + * Atomically advance counter to the new value. Interrupts, vcpu + * scheduling, and scaling inaccuracies can cause cputime_advance + * to be occasionally called with a new value smaller than counter. + * Let's enforce atomicity. + * + * Normally a caller will only go through this loop once, or not + * at all in case a previous caller updated counter the same jiffy. + */ +static void cputime_advance(cputime_t *counter, cputime_t new) +{ + cputime_t old; + + while (new > (old = ACCESS_ONCE(*counter))) + cmpxchg_cputime(counter, old, new); +} + /* * Adjust tick based cputime random precision against scheduler * runtime accounting. @@ -599,16 +616,8 @@ static void cputime_adjust(struct task_cputime *curr, utime = rtime - stime; } - /* - * If the tick based count grows faster than the scheduler one, - * the result of the scaling may go backward. - * Let's enforce monotonicity. - * Atomic exchange protects against concurrent cputime_adjust(). - */ - while (stime > (rtime = ACCESS_ONCE(prev->stime))) - cmpxchg(&prev->stime, rtime, stime); - while (utime > (rtime = ACCESS_ONCE(prev->utime))) - cmpxchg(&prev->utime, rtime, utime); + cputime_advance(&prev->stime, stime); + cputime_advance(&prev->utime, utime); out: *ut = prev->utime;