From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-Id: <20120217005510.559345291@linuxfoundation.org> Date: Thu, 16 Feb 2012 16:55:14 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Peter Zijlstra , Ilya Tumaykin , Wu Fengguang Subject: [05/15] lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel In-Reply-To: <20120217005650.GA17119@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Wu Fengguang 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 Reported-by: Ilya Tumaykin Tested-by: Ilya Tumaykin Signed-off-by: Wu Fengguang Signed-off-by: Greg Kroah-Hartman --- 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)