deadlock in with fifo reading in tests/dd/no-allocate.sh

[Pádraig Brady]

I noticed _once_ a deadlock in dd in tests/dd/no-allocate.sh
with make -j20 on a solaris 10 system.
Does anyone see why a dd process would deadlock here?

http://git.sv.gnu.org/gitweb/?p=coreutils.git;a=blob;f=tests/dd/no-allocate.sh;h=dd1a7408b

Now I haven't reproduced the deadlock, but I don't
immediately see why it should deadlock.

I see that the dd processes can go away without reading
due to the ulimit. But that would only cause multiple
`echo 1 > tape` instances to hang around which would
surely give less chance for subsequent dd processes to hang?

I considered adding a 'wait' after each (ulimit...)
but that could introduce a deadlock given the dd
process may go away even before the subshell opens the fifo,
especially for the `dd seek=1` case which can proceed
through an open(RDWR); malloc(large); and be killed even
before the background process blocks.

So I'll probably redo this test, or at least
mark it expensive so it's not run by default.

thanks,
Pádraig.