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Bug#82600: zalloc panic

From: Roland McGrath
Subject: Bug#82600: zalloc panic
Date: Sun, 28 Jan 2001 20:22:12 -0500 (EST)

Oh, well, I just now actually looked at your script and realized that you
are running a fork bomb.  Which is to say, the essence of that program is
the same as "while (fork () == 0) ;".  Such a program always ends in a
pathological resource shortage.  Unix has things like per-owner (uid)
resource limits on the number of processes that can prevent this (but won't
if you're root).

It is certainly the case that the kernel behaves poorly (i.e. panics a lot)
in all sorts of extreme resource shortage situations.  That is not good,
but it would be tedious at best and perhaps really a lot of hard work to
make it better in Mach.  

There are doubtless nonrobustnesses in the Hurd code as well when it comes
to resource shortages.  It would a fine thing to find those and fix them.
But the kernel dies before those really get exposed.

Though not directly relevant to your report (since it runs as root), real
resource limits are also definitely a good thing to have.  We really have
nothing meaningful in the Hurd; we don't even include resource limits in
the protocols for inheritance by exec and such.  Many resource controls can
only actually be enforced by the kernel, because its interfaces give direct
access to kernel resources (vm_allocate, task_create, et al).  Some such
controls might not be too hard to implement.

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