user mode backtrace

[David Boreham]

I'd like to get a stack trace for the process that made the
system call I'm probing (I'm looking at filesystem access
typically, so reads/writes/syncs etc). The systemtap backtrace
function appears to only get the kernel mode stack which
is not much use to me. I was wondering if anyone had
discovered a good solution to this problem already ?
I was thinking perhaps I could invoke pstack (gdb)
on the current pid/tid. But I'm worried that doing so
might deadlock since the process is inside a system
call.

I'm looking at a very large application that beats up on
the filesystem, in case you're wondering why I want to do
this. It's so large that nobody is quite sure what code
access which files, when and why.

Thanks.