Can I coredump a process that is blocking on disk activity (preferably without killing it)?

Question

I want to dump the core of a running process that is, according to /proc/<pid>/status, currently blocking on disk activity. Actually, it is busy doing work on the GPU (should be 4 hours of work, but it has taken significantly longer now). I would like to know how much of the process's work has been done, so it'd be good to be able to dump the process's memory. However, as far as I know, "blocking on disk activity" means that it's not possible to interrupt the process in any way, and coredumping a process e.g. using gdb requires interrupting and temporarily stopping the process in order to attach via ptrace, right?

I know that I could just read /proc/<pid>/{maps,mem} as root to get the (maybe inconsistent) memory state, but I don't know any way to get hold of the process's userspace CPU register values... they stay the same while the process is inside the kernel, right?

Answer 1

You can probably run gcore on your program. It's basically a wrapper around GDB that attaches, uses the gcore command, and detaches again.

This might interrupt your IO (as if it received a signal, which it will), but your program can likely restart it if written correctly (and this may occur in any case, due to default handling).