sched, time: Fix build error with 64 bit cputime_t on 32 bit systems
On 32 bit systems cmpxchg cannot handle 64 bit values, so
some additional magic is required to allow a 32 bit system
with CONFIG_VIRT_CPU_ACCOUNTING_GEN=y enabled to build.
Make sure the correct cmpxchg function is used when doing
an atomic swap of a cputime_t.
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: umgwanakikbuti@gmail.com
Cc: fweisbec@gmail.com
Cc: srao@redhat.com
Cc: lwoodman@redhat.com
Cc: atheurer@redhat.com
Cc: oleg@redhat.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linux390@de.ibm.com
Cc: linux-arch@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s390@vger.kernel.org
Link: http://lkml.kernel.org/r/20140930155947.070cdb1f@annuminas.surriel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/powerpc/include/asm/cputime.h b/arch/powerpc/include/asm/cputime.h
index 607559a..6c840ce 100644
--- a/arch/powerpc/include/asm/cputime.h
+++ b/arch/powerpc/include/asm/cputime.h
@@ -32,6 +32,8 @@
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 f65bd36..3001887 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 d5cb78f5..fe386fc 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 4e81760..0419485 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 64492df..8394b1e 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -555,6 +555,23 @@
}
/*
+ * 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 @@
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;