lib/flex_proportions.c: fix corruption of denominator in flexible proportions
authorJan Kara <jack@suse.cz>
Tue, 25 Sep 2012 00:17:35 +0000 (17:17 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Tue, 25 Sep 2012 15:59:21 +0000 (08:59 -0700)
commitb5bd6a0e5fa8c0376d9746c566fe3daaa51ec825
treeac746aa7a4f21b9ac4161b66fce9965ffeda9cb1
parent0e75898fe2499ece0ac3f1475982a828b3283b0d
lib/flex_proportions.c: fix corruption of denominator in flexible proportions

When racing with CPU hotplug, percpu_counter_sum() can return negative
values for the number of observed events.

This confuses fprop_new_period(), which uses unsigned type and as a
result number of events is set to big *positive* number.  From that
moment on, things go pear shaped and can result e.g.  in division by
zero as denominator is later truncated to 32-bits.

This bug causes a divide-by-zero oops in bdi_dirty_limit() in Borislav's
3.6.0-rc6 based kernel.

Fix the issue by using a signed type in fprop_new_period().  That makes
us bail out from the function without doing anything (mistakenly)
thinking there are no events to age.  That makes aging somewhat
inaccurate but getting accurate data would be rather hard.

Signed-off-by: Jan Kara <jack@suse.cz>
Reported-by: Borislav Petkov <bp@amd64.org>
Reported-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
lib/flex_proportions.c