From owner-freebsd-bugs  Tue Apr  2 10:51:22 2002
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Date: Tue, 2 Apr 2002 10:51:12 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
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To: freebsd-bugs@FreeBSD.ORG,
	"Dorr H. Clark" <dclark@applmath.scu.edu>
Subject: Re: kern/36504: crash/panic vm_object_allocate under file system code w/fix
References:  <200204020819.g328JPJ21423@freefall.freebsd.org>
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X-Loop: FreeBSD.org

    Ok, I've looke at this some more.  The second part of the patch
    created a little confusion because you diff'd the files backwards, but
    I see what you are doing.

    But there's a problem.  Actually several problems.  The biggest one is
    that many filesystems, including UFS uses VM backing store heavily.
    If the object creation fails, UFS is screwed up and so is any user
    program that uses mmap() on the file in question.  So we can't allow it
    to fail.

    Second problem: vm_object_allocate() assumes that the zalloc() will
    succeed.  The system must be crashing in there, before your defensive
    check.

    The only thing that can cause vm_object_allocate() to fail that I know
    of is if the system runs out of KVM.  If the system runs out of KVM the
    system is in real trouble.  I will make changes that check for the 
    zalloc failure and panic the system, but that's about the best I can do
    for the moment.

    What you need to do if you are experiencing crashes is to compile up a
    debug kernel and obtain a crash dump.  I should be able to diagnose
    the cause of the crash from that.

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>


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