Ilya, would you post your /proc/vmstat? I wonder if your proportion shift value is really large enough (> 32) to trigger bug in this way. Thanks, Fengguang On Tue, Jan 10, 2012 at 10:54:55PM +0800, Wu Fengguang wrote: > 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 > > Tested-by: Ilya Tumaykin <librarian_rus@xxxxxxxxx> > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > --- > include/linux/proportions.h | 4 ++++ > 1 file changed, 4 insertions(+) > > --- linux.orig/include/linux/proportions.h 2012-01-09 11:51:19.000000000 +0800 > +++ linux/include/linux/proportions.h 2012-01-09 11:53:47.000000000 +0800 > @@ -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) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
