求助各位，linux6.4 apache集群挂接nfs存储，进程频繁block

lucia0919

   公司4台dell r710 服务器，安装linux 6.4，内核Linux apache4 2.6.32-358.el6.x86_64，apache版本为2.23,每台挂载了NAS存储（发布的程序文件放置在NAS存储上），nfsv4挂接，apache为worker模式（多线程）。每隔几天应用就不能访问，查看后台服务器80端口是监听状态，页面打开为空白。系统报错如下：
INFO: task httpd:14779 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
httpd         D 0000000000000001     0 14779   2574 0x00000000
ffff880329727ba8 0000000000000086 ffff880329727b28 ffff880325e8ff00
ffff880329727b28 ffffffff8119af4a ffff880325e8fe40 ffff880325e8ff00
ffff8803292e4638 ffff880329727fd8 000000000000fb88 ffff8803292e4638
Call Trace:
[<ffffffff8119af4a>] ? dput+0x9a/0x150
[<ffffffff8150ed3e>] __mutex_lock_slowpath+0x13e/0x180
[<ffffffff8150ebdb>] mutex_lock+0x2b/0x50
[<ffffffff8119037b>] do_lookup+0x11b/0x230
[<ffffffff81190bc4>] __link_path_walk+0x734/0x1030
[<ffffffff81180b5b>] ? do_sync_readv_writev+0xfb/0x140
[<ffffffff8119174a>] path_walk+0x6a/0xe0
[<ffffffff8119191b>] do_path_lookup+0x5b/0xa0
[<ffffffff811925a7>] user_path_at+0x57/0xa0
[<ffffffff815101ab>] ? _spin_unlock_bh+0x1b/0x20
[<ffffffff811869bc>] vfs_fstatat+0x3c/0x80
[<ffffffff8148c272>] ? do_tcp_setsockopt+0x102/0x490
[<ffffffff81186b2b>] vfs_stat+0x1b/0x20
[<ffffffff81186b54>] sys_newstat+0x24/0x50
[<ffffffff8148c65a>] ? tcp_setsockopt+0x2a/0x30
[<ffffffff81437ea4>] ? sock_common_setsockopt+0x14/0x20
[<ffffffff81436670>] ? sys_setsockopt+0xd0/0xe0
[<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
相同的挂载方式，相同的apache配置，在soalris系统上跑得很稳定，linux就不行。被这个问题困扰好久了，优化过系统和apache参数，系统内核也升级到了最新版本，修改了nfs的挂接参数，还是未能解决。求各位高手指点，小妹感激不尽。