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The ls command has hang for a long time while executing dd in the NFS client

Publication Date:  2012-11-26 Views:  80 Downloads:  0
Issue Description
Create the NFS share file system in the N8000, after the Linux client mounting, execute “dd” command but it hang:
1. In the N8000, create the NFS share and the NFS server status is normal:
gensys.NFS> share show
    /vx/fs222               * (rw,sync,secure,no_root_squash,wdelay)
    gensys.NFS> server status
    NFS Status on gensys_01 : ONLINE
    NFS Status on gensys_02 : ONLINE

2. Create the share catalog in the client, and mount to the “N8000 /vx/fs222” file system.
DS-client7:~ # mkdir fs222     # create the share catalog “fs222”
    DS-client7:~ # mount -t nfs 129.23.69.150:/vx/fs222 /fs222 # mount via the default parameters
    DS-client7:~ # mount    #  view the mounting status
    ……
    129.23.69.150:/vx/fs222 on /fs222 type nfs (rw,addr=129.23.69.150) # display the successful mounted share catalog
3. Execute the “dd” command:
DS-client7:~   # cd /fs222/
    DS-client7:/fs222   # dd if=/dev/zero of=50g.data bs=1M count=50000
4. Execute the “ls” command:
DS-client7:/ # cd fs222/
DS-client7:/fs222     #ls command has been “hang”, and it has been hang for about 2 minutes
5. View the logs:
DS-client7:~ # echo t>/proc/sysrq-trigger  # export the information of the thread status
    DS-client7:~ # tailf /var/log/messages
    May 17 12:48:32 DS-client7 kernel: [351714.363671] Call Trace:
    ……
    vt_event_wait 0x9f/0x120  # after the “io” event has completed, the “dd” command has occupied the lots of system resource for a long time, and causes the “ls” command can’t respond.
    vt_waitactive 0x2d/0x60   # wait to active the io event.
    vt_ioctl 0xf67/0x1cd0
    tty_ioctl 0x38b/0x900
    vfs_ioctl 0x2f/0xb0       # call the “vfs io” request.
    do_vfs_ioctl 0x36b/0x3e0
    sys_ioctl 0xa1/0xb0
    ……

Alarm Information
None

Handling Process
Modify the priority of the “dd” command in the operating system, and make a equilibrium mechanism of the operating system resources, so the system can’t make any single service occupying the system resource and then causes the other services can’t implement.

Root Cause
Build the NFS server via the standard Linux and compare with the clients of two different operating systems, execute the “dd” command in the share catalog, and then execute the “ls” command, it has been hang in the two operating systems. Execute the “cp” command to copy the file in the share catalog, and then execute the “ls” command again, hence, it can’t hang any longer.
The detail information is not known.

Suggestions
None

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