| From 3310225dfc71a35a2cc9340c15c0e08b14b3c754 Mon Sep 17 00:00:00 2001 |
| From: Wu Fengguang <fengguang.wu@intel.com> |
| Date: Mon, 9 Jan 2012 11:53:50 -0600 |
| Subject: lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel |
| |
| From: Wu Fengguang <fengguang.wu@intel.com> |
| |
| commit 3310225dfc71a35a2cc9340c15c0e08b14b3c754 upstream. |
| |
| PROP_MAX_SHIFT should be set to <=32 on 64-bit box. This fixes two bugs |
| in the below lines of bdi_dirty_limit(): |
| |
| bdi_dirty *= numerator; |
| do_div(bdi_dirty, denominator); |
| |
| 1) divide error: do_div() only uses the lower 32 bit of the denominator, |
| which may trimmed to be 0 when PROP_MAX_SHIFT > 32. |
| |
| 2) overflow: (bdi_dirty * numerator) could easily overflow if numerator |
| used up to 48 bits, leaving only 16 bits to bdi_dirty |
| |
| Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> |
| Reported-by: Ilya Tumaykin <librarian_rus@yahoo.com> |
| Tested-by: Ilya Tumaykin <librarian_rus@yahoo.com> |
| Signed-off-by: Wu Fengguang <fengguang.wu@intel.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| include/linux/proportions.h | 4 ++++ |
| 1 file changed, 4 insertions(+) |
| |
| --- a/include/linux/proportions.h |
| +++ b/include/linux/proportions.h |
| @@ -81,7 +81,11 @@ void prop_inc_percpu(struct prop_descrip |
| * Limit the time part in order to ensure there are some bits left for the |
| * cycle counter and fraction multiply. |
| */ |
| +#if BITS_PER_LONG == 32 |
| #define PROP_MAX_SHIFT (3*BITS_PER_LONG/4) |
| +#else |
| +#define PROP_MAX_SHIFT (BITS_PER_LONG/2) |
| +#endif |
| |
| #define PROP_FRAC_SHIFT (BITS_PER_LONG - PROP_MAX_SHIFT - 1) |
| #define PROP_FRAC_BASE (1UL << PROP_FRAC_SHIFT) |