How to find which system call the process in?

Hi,
One of my process changes to state 'D' which means uninterrupt
sleep. I want to check out in which system call this process stay.
But I can't strace it because the strace program will be 'D' too. And
I can't use gdb to attach it, because an uninterrupt sleeping process
can't deal with any signal. How can check out the system call my
process sleep in?
I am using Linux system, thanks!

Regards!
Bo
.

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