diff options
| author | Wu Fengguang <fengguang.wu@intel.com> | 2012-01-09 11:53:50 -0600 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-03-04 09:49:19 -0800 |
| commit | 210e889ab890de2eceb8b650093618937d9c1c45 (patch) | |
| tree | 1673eaf865ac5125cd5b3be1586f67e50c38cfd2 | |
| parent | 5fe6345243aba30d20772c8f04cce098c6752425 (diff) | |
| download | lwn-210e889ab890de2eceb8b650093618937d9c1c45.tar.gz lwn-210e889ab890de2eceb8b650093618937d9c1c45.zip | |
lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel
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>
| -rw-r--r-- | include/linux/proportions.h | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/include/linux/proportions.h b/include/linux/proportions.h index cf793bbbd05e..22653d7c3f8d 100644 --- a/include/linux/proportions.h +++ b/include/linux/proportions.h @@ -81,7 +81,11 @@ void prop_inc_percpu(struct prop_descriptor *pd, struct prop_local_percpu *pl) * 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) |