From: Wu Fengguang <fengguang.wu@intel.com>
Date: Mon, 9 Jan 2012 17:53:50 +0000 (-0600)
Subject: lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel
X-Git-Tag: v3.3-rc4~36^2~1
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3310225dfc71a35a2cc9340c15c0e08b14b3c754;p=pandora-kernel.git

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>
---

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