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| author | Wu Fengguang <fengguang.wu@intel.com> | 2012-01-09 11:53:50 -0600 |
|---|---|---|
| committer | Wu Fengguang <fengguang.wu@intel.com> | 2012-02-01 16:53:46 +0800 |
| commit | 3310225dfc71a35a2cc9340c15c0e08b14b3c754 (patch) | |
| tree | 0475693eddb964dd8ea125e59f9e9efbcabd1dd0 /include/linux/proportions.h | |
| parent | 15eb77a07c714ac80201abd0a9568888bcee6276 (diff) | |
| download | lwn-3310225dfc71a35a2cc9340c15c0e08b14b3c754.tar.gz lwn-3310225dfc71a35a2cc9340c15c0e08b14b3c754.zip | |
lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel
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: <stable@kernel.org>
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>
Diffstat (limited to 'include/linux/proportions.h')
| -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 ef35bb73f69b..26a8a4ed9b07 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) |