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author | Tejun Heo <tj@kernel.org> | 2015-04-21 16:49:13 -0400 |
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committer | Jens Axboe <axboe@fb.com> | 2015-04-23 10:36:33 -0600 |
commit | 464d1387acb94dc43ba772b35242345e3d2ead1b (patch) | |
tree | d331377c5d30736d8538dafcdb91709e593bf239 /block | |
parent | 2a34c0872adf252f23a6fef2d051a169ac796cef (diff) | |
download | linux-464d1387acb94dc43ba772b35242345e3d2ead1b.tar.bz2 |
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 <tj@kernel.org>
Cc: stable@vger.kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block')
0 files changed, 0 insertions, 0 deletions