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[PATCH 0/2] xfs: fix inode count underrun

To: xfs@xxxxxxxxxxx
Subject: [PATCH 0/2] xfs: fix inode count underrun
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 6 May 2015 08:01:37 +1000
Cc: linux-kernel@xxxxxxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
Hi folks,

With the conversion of XFS to use the generic per-cpu superblocks, I
overlooked the fact that the update batch size is important to the
accuracy of the comparison function. Using different batch sizes
means percpu_counter_compare() doesn't detect when it should fall
back to percpu_counter_sum() for accuracy correctly, resulting in
counter comparisons being inaccurate. This leads to problems with
zero threshold detection in XFS.

To fix, add __percpu_counter_compare() to take a caller supplied
batch size. This fixes the XFS regression introduced in 4.1-rc1.

-Dave.

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