Messages in this thread Patch in this message | | | Date | Mon, 12 Mar 2012 01:44:22 +0100 | From | Willy Tarreau <> | Subject | [ 11/13] lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel |
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2.6.27-longterm review patch. If anyone has any objections, please let me know.
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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 files changed, 4 insertions(+), 0 deletions(-)
diff --git a/include/linux/proportions.h b/include/linux/proportions.h index cf793bb..22653d7 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) -- 1.7.2.1.45.g54fbc
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