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Message-Id: <199902151943.LAA18818@apollo.backplane.com>
Date: Mon, 15 Feb 1999 11:43:57 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
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Subject: kern/10107: inode vs exec_map interlock
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>Number:         10107
>Category:       kern
>Synopsis:       interlock situation with exec_map and a program binary inode
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Feb 15 11:50:01 PST 1999
>Closed-Date:
>Last-Modified:
>Originator:     Matthew Dillon
>Release:        FreeBSD 4.0-CURRENT i386
>Organization:
none
>Environment:

	Heavily loaded test machine artificially limited to 16MB of main
	memory, NFS swap, running a buildworld -j10.

>Description:

    I found an interesting interlock situation between what I believe to
    be a program binaries inode and the exec_map.  The machine locked up
    trying to exec new programs.

    This was running a make -j10 buildworld on a machine with 16MB of ram
    configured, while testing my new VM system.  I don't think the lockup is 
    due to my VM system, though.  It took it 7 hours of extremely heavy
    paging before it locked up.

    When I broke the machine out into DDB and did a ps, all of the cc's
    were stuck in 'inode' wait, while a single ld program was stuck in
    'thrd_sleep'.

    I tracked 'thrd_sleep' down to a vm_map lock and the map down to
    the exec_map.  I tracked down the inode lock to the 'cc' program binary.
    The inode had one shared lock and 7 waiters.  The exec_map appears to
    own one shared lock with 6 waiters ( but most of the waiters are due to
    me trying to run other programs before breaking into the DDB ).

    I am guessing that there is an interlock situation with exec_map and
    a program inode where one process locks exec_map followed by the program
    inode, and another locks the program inode followed by exec_map.  But 
    I'm not familiar with that section of the code so I would appreciate
    any help.

>How-To-Repeat:

    The problem was found by running a make -j10 buildworld on a machine
    artificially limited to 16MB of main memory, with NFS swap.  The problem
    occured approximately 7 hours into the buildworld so it is presumably
    difficult to recreate and represents a small window somewhere.

>Fix:
	
	Unknown as yet.

>Release-Note:
>Audit-Trail:
>Unformatted:

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