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[PATCH] xfs: use percpu_counter_compare instead of naive comparing

To: xfs@xxxxxxxxxxx
Subject: [PATCH] xfs: use percpu_counter_compare instead of naive comparing
From: xuw2015@xxxxxxxxx
Date: Fri, 17 Apr 2015 10:22:24 +0800
Cc: George Wang <xuw2015@xxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
From: George Wang <xuw2015@xxxxxxxxx>

Function percpu_counter_read just return the current counter, regardless of
every cpu's count. This counter can be negative value, which will cause the
checking of "allocated inode counts <= m_maxicount" false positive.
Commit 501ab3238753 "xfs: use generic percpu counters for inode counter
" introduced this problem.
Use the percpu_counter_compare, which will first do stuff in current cpu for
performance; if can not get the result, it will get the exactly counter
based on the count of every cpu.

Signed-off-by: George Wang <xuw2015@xxxxxxxxx>
---
 fs/xfs/libxfs/xfs_ialloc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
index 07349a1..af9e7d2 100644
--- a/fs/xfs/libxfs/xfs_ialloc.c
+++ b/fs/xfs/libxfs/xfs_ialloc.c
@@ -376,8 +376,8 @@ xfs_ialloc_ag_alloc(
         */
        newlen = args.mp->m_ialloc_inos;
        if (args.mp->m_maxicount &&
-           percpu_counter_read(&args.mp->m_icount) + newlen >
-                                                       args.mp->m_maxicount)
+           percpu_counter_compare(&args.mp->m_icount,
+                                       args.mp->m_maxicount - newlen) > 0)
                return -ENOSPC;
        args.minlen = args.maxlen = args.mp->m_ialloc_blks;
        /*
@@ -1341,8 +1341,8 @@ xfs_dialloc(
         * inode.
         */
        if (mp->m_maxicount &&
-           percpu_counter_read(&mp->m_icount) + mp->m_ialloc_inos >
-                                                       mp->m_maxicount) {
+           percpu_counter_compare(&mp->m_icount,
+                               mp->m_maxicount - mp->m_ialloc_inos) > 0) {
                noroom = 1;
                okalloc = 0;
        }
-- 
1.9.3

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