Because I already jail break the iPad with green poison . If upgrade any problem?
Which iPad do you have, the iPad1 or the iPad2?
Because if you have the iPad1, then you can upgrade to iOS 5.1 and, after a bit of computer work, you can most likely re-jail break it. You'll have a tethered jail break, but that has not caused some members here any trouble.
If you have an iPad2, you cannot upgrade to iOS 5.1 and keep that jailbreak. CANNOT. If you upgrade, you will have to be stock and wait for a jail break to be released (if it ever does). Your jail break will be gone.
Of course, if you're goal is to be stock, then either version of iPad can be easily upgraded to iOS 5.1 - but, again, the jail break will be gone.
Hope this helps.
Marilyn
P.S. And, since this is a question about jail breaking, I will move it out of the polls section over to the Hacking section, where the jail breakers hang out...