From owner-freebsd-bugs  Wed Feb 16 11: 6:36 2000
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Date: Wed, 16 Feb 2000 11:06:34 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
Message-Id: <200002161906.LAA53213@apollo.backplane.com>
To: sheldonh@FreeBSD.ORG, freebsd-bugs@FreeBSD.ORG
Subject: Re: kern/16573: extensive fork()+mmap() causes 4.0 kernel to panic()
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:Synopsis: extensive fork()+mmap() causes 4.0 kernel to panic()
:
:Responsible-Changed-From-To: freebsd-bugs->dillon
:Responsible-Changed-By: sheldonh
:Responsible-Changed-When: Wed Feb 16 00:43:53 PST 2000
:Responsible-Changed-Why: 
:Matt, is the panic in vm_map_insert() expected behaviour inside an
:mmapping fork-bomb?

    The kernel does not limit the number of mappings any given process can
    make and when you combine that with fork() it's fairly easy to run 
    the kernel out of resources.  Your test program ran the kernel out of
    vm_entry structures.  vm_map_insert() is just assuming that its allocation
    will succeed when, in fact, NULL can be returned.  Unfortunately at this
    point returning an error would not help - with the system totally run
    out of vm_map_entry structures it's effectively dead.

    We should be able to fix this with a per-process sysctl limit on the
    number of entries allowed in a vm_map structure.  When combined with
    a reasonable maxproc limit for users (like 40) it ought to protect
    against this situation.  I'll ask Jordan if I can make that change prior
    to release but if not we can definitely fix it after release.

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>


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