Same problem happened again, below is the system.log:
Mar 19 18:50:21 kernel: nas/389: potentially unexpected fatal signal 6.
Mar 19 18:50:21 kernel: Pid: 389, comm: nas
Mar 19 18:50:21 kernel: CPU: 1 Tainted: P (2.6.36.4brcmarm #1)
Mar 19 18:50:21 kernel: PC is at 0x401f1340
Mar 19 18:50:21 kernel: LR is at 0x4022f090
Mar 19 18:50:21 kernel: pc : [<401f1340>] lr : [<4022f090>] psr: 60000010
Mar 19 18:50:21 kernel: sp : beda91b8 ip : 402488f8 fp : 0007f420
Mar 19 18:50:21 kernel: r10: 0007f35c r9 : beda994e r8 : beda92fe
Mar 19 18:50:21 kernel: r7 : 00000025 r6 : 00000000 r5 : 40249280 r4 : 402484f8
Mar 19 18:50:21 kernel: r3 : 00004d64 r2 : 000009a0 r1 : 00000006 r0 : 00000000
Mar 19 18:50:21 kernel: Flags: nZCv IRQs on FIQs on Mode USER_32 ISA ARM Segment user
Mar 19 18:50:21 kernel: Control: 10c53c7d Table: 9dbd804a DAC: 00000015
Mar 19 18:50:23 syslog: wlceventd_proc_event(530): wl1.1: Auth 98:A5:43:44:45:14, status: Successful (0), rssi:0
Mar 19 18:50:23 syslog: wlceventd_proc_event(540): wl1.1: ReAssoc 98:A5:43:44:45:14, status: Successful (0), rssi:0
Mar 19 18:50:23 syslog: wlceventd_proc_event(511): wl0.1: Disassoc 98:A5:43:44:45:14, status: 0, reason: Disassociated because sending station is leaving (or has left) BSS (8), rssi:0
Mar 19 18:50:29 syslog: wlceventd_proc_event(494): wl1.1: Deauth_ind 98:A5:43:44:45:14, status: 0, reason: 4-way handshake timeout (f), rssi:0
Mar 19 18:50:32 syslog: wlceventd_proc_event(530): wl1.1: Auth 98:A5:43:44:45:14, status: Successful (0), rssi:0
Mar 19 18:50:32 syslog: wlceventd_proc_event(559): wl1.1: Assoc 98:A5:43:44:45:14, status: Successful (0), rssi:0
Mar 19 18:50:38 syslog: wlceventd_proc_event(494): wl1.1: Deauth_ind 98:A5:43:44:45:14, status: 0, reason: 4-way handshake timeout (f), rssi:0
Mar 19 18:52:35 syslog: wlceventd_proc_event(530): wl0.1: Auth 18:3E:AA:BB:CC:99, status: Successful (0), rssi:0
Mar 19 18:52:35 syslog: wlceventd_proc_event(540): wl0.1: ReAssoc 18:3E:AA:BB:CC:99, status: Successful (0), rssi:0
Mar 19 18:52:35 syslog: wlceventd_proc_event(511): wl1.1: Disassoc 18:3E:AA:BB:CC:99, status: 0, reason: Disassociated because sending station is leaving (or has left) BSS (8), rssi:0
Mar 19 18:52:41 syslog: wlceventd_proc_event(494): wl0.1: Deauth_ind 18:3E:AA:BB:CC:99, status: 0, reason: 4-way handshake timeout (f), rssi:0
Mar 19 18:52:46 syslog: wlceventd_proc_event(530): wl1.1: Auth 18:3E:AA:BB:CC:99, status: Successful (0), rssi:0
Mar 19 18:52:46 syslog: wlceventd_proc_event(559): wl1.1: Assoc 18:3E:AA:BB:CC:99, status: Successful (0), rssi:0
Mar 19 18:52:52 syslog: wlceventd_proc_event(494): wl1.1: Deauth_ind 18:3E:AA:BB:CC:99, status: 0, reason: 4-way handshake timeout (f), rssi:0