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authorRik van Riel <riel@redhat.com>2014-09-30 15:59:47 -0400
committerIngo Molnar <mingo@kernel.org>2014-10-03 05:46:55 +0200
commit347abad981c1ef815ea5ba861adba6a8c6aa1580 (patch)
treeea18690dcb71d23c29a92a602c1d5373f9360e7a /kernel
parent43f4d66637bc752e93a77ff2536474a5a3888442 (diff)
downloadop-kernel-dev-347abad981c1ef815ea5ba861adba6a8c6aa1580.zip
op-kernel-dev-347abad981c1ef815ea5ba861adba6a8c6aa1580.tar.gz
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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/cputime.c29
1 files changed, 19 insertions, 10 deletions
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 @@ drop_precision:
}
/*
+ * 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;
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