div64_u64(): improve precision on 32bit platforms

The current implementation of div64_u64 for 32bit systems returns an
approximately correct result when the divisor exceeds 32bits.  Since doing
64bit division using 32bit hardware is a long since solved problem we just
use one of the existing proven methods.

Additionally, add a div64_s64 function to correctly handle doing signed
64bit division.

Addresses https://bugzilla.redhat.com/show_bug.cgi?id=616105

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Ben Woodard <bwoodard@llnl.gov>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Mark Grondona <mgrondona@llnl.gov>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 77b04ed037df..450092c1e35f 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -173,6 +173,11 @@ extern int _cond_resched(void);
                 (__x < 0) ? -__x : __x;         \
         })
 
+#define abs64(x) ({                             \
+                s64 __x = (x);                  \
+                (__x < 0) ? -__x : __x;         \
+        })
+
 #ifdef CONFIG_PROVE_LOCKING
 void might_fault(void);
 #else