From: Tejun Heo Date: Tue, 21 Apr 2015 20:49:13 +0000 (-0400) Subject: writeback: use |1 instead of +1 to protect against div by zero X-Git-Tag: omap-for-v4.2/omap1-v2~18^2~6 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=464d1387acb94dc43ba772b35242345e3d2ead1b;p=pandora-kernel.git writeback: use |1 instead of +1 to protect against div by zero mm/page-writeback.c has several places where 1 is added to the divisor to prevent division by zero exceptions; however, if the original divisor is equivalent to -1, adding 1 leads to division by zero. There are three places where +1 is used for this purpose - one in pos_ratio_polynom() and two in bdi_position_ratio(). The second one in bdi_position_ratio() actually triggered div-by-zero oops on a machine running a 3.10 kernel. The divisor is x_intercept - bdi_setpoint + 1 == span + 1 span is confirmed to be (u32)-1. It isn't clear how it ended up that but it could be from write bandwidth calculation underflow fixed by c72efb658f7c ("writeback: fix possible underflow in write bandwidth calculation"). At any rate, +1 isn't a proper protection against div-by-zero. This patch converts all +1 protections to |1. Note that bdi_update_dirty_ratelimit() was already using |1 before this patch. Signed-off-by: Tejun Heo Cc: stable@vger.kernel.org Reviewed-by: Jan Kara Signed-off-by: Jens Axboe --- Reading git-diff-tree failed