Comment 3 for bug 498525

Ok this has changed recently. It is part of a new mechanism for detecting recursive core-dump, ie. dumps in the core dump handler. This changed in the commit below:

  commit 725eae32df7754044809973034429a47e6035158
  Author: Neil Horman <email address hidden>
  Date: Wed Sep 23 15:56:54 2009 -0700

    exec: make do_coredump() more resilient to recursive crashes

    Change how we detect recursive dumps.

    Currently we have a mechanism by which we try to compare pathnames of the
    crashing process to the core_pattern path. This is broken for a dozen
    reasons, and just doesn't work in any sort of robust way.

    I'm replacing it with the use of a 0 RLIMIT_CORE value. Since helper apps
    set RLIMIT_CORE to zero, we don't write out core files for any process
    with that particular limit set. It the core_pattern is a pipe, any
    non-zero limit is translated to RLIM_INFINITY.

    This allows complete dumps to be captured, but prevents infinite recursion
    in the event that the core_pattern process itself crashes.

    [<email address hidden>: coding-style fixes]
    Signed-off-by: Neil Horman <email address hidden>
    Reported-by: Earl Chew <email address hidden>
    Cc: Oleg Nesterov <email address hidden>
    Cc: Andi Kleen <email address hidden>
    Cc: Alan Cox <email address hidden>
    Signed-off-by: Andrew Morton <email address hidden>
    Signed-off-by: Linus Torvalds <email address hidden>

The practicle upshot of which seems to be that setting the limit to 0 stops coredumps even for pipes. However, setting it to a very low value, say 1, will restore the original behaviour without allowing a real dump to occur where pipes are not in use.