OS hanged (BUG: soft lockup - CPU#0 stuck for 60s! [httpd:xxxx]).

Issue

• OS was hung, this occurred several times.
• Checking a vmcore which was collected by push of NMI switch, it was seen that it was in a state of spin lock during httpd processes as follows.

crash> log
        : <snip>
BUG: soft lockup - CPU#0 stuck for 60s! [httpd:26249]

Pid: 26249, comm:                httpd
EIP: 0060:[<c0620ac3>] CPU: 0
EIP is at _spin_lock+0xa/0xf
 EFLAGS: 00000282    Tainted: P       (2.6.18-238.el5 #1)
EAX: c0706880 EBX: db804d50 ECX: c9ffd960 EDX: 00000001
ESI: c0706880 EDI: f75ae600 EBP: f2ab6568 DS: 007b ES: 007b
CR0: 8005003b CR2: b7fa2000 CR3: 123d5000 CR4: 000006d0
 [<c04ee6d2>] _atomic_dec_and_lock+0x2a/0x44
 [<c048c87b>] dput+0x22/0xed
 [<c0477e2f>] __fput+0x15c/0x184
 [<c0475751>] filp_close+0x4e/0x54
 [<c047698a>] sys_close+0x71/0xa0
 [<c0404f4b>] syscall_call+0x7/0xb
 =======================
BUG: soft lockup - CPU#1 stuck for 60s! [httpd:26183]

Pid: 26183, comm:                httpd
EIP: 0060:[<c0620ac3>] CPU: 1
EIP is at _spin_lock+0xa/0xf
 EFLAGS: 00000282    Tainted: P       (2.6.18-238.el5 #1)
EAX: c0706880 EBX: f68468f0 ECX: c0487f8d EDX: d3231f98
ESI: d3443e40 EDI: f4580884 EBP: f45808f8 DS: 007b ES: 007b
CR0: 8005003b CR2: 091f21ac CR3: 1b945000 CR4: 000006d0
 [<f938a51c>] rfs_readdir+0x38/0x1b4 [redirfs]
 [<c0487f8d>] filldir+0x0/0xb9
 [<c0475a55>] do_filp_open+0x2b/0x31
 [<c04880a9>] vfs_readdir+0x63/0x8d
 [<c0487f8d>] filldir+0x0/0xb9
 [<c04882f7>] sys_getdents+0x5f/0x9c
 [<c0404f4b>] syscall_call+0x7/0xb
 =======================
        : <snip>