valid dup lock logic for witness

From: John-Mark Gurney (gurney_j_at_resnet.uoregon.edu)
Date: 08/07/04

  • Next message: Conrad J. Sabatier: "Re: install_and_reboot target for kernel's..." 
    Date: Fri, 6 Aug 2004 15:43:16 -0700
To: freebsd-arch@freebsd.org

    I have been working on kqueue, and to support kq in kq, I need to obtain
    two kq locks (both of the same type) at the same time. Normally this can
    cause a deadlock, but using a proper lock ordering strategy, it can be
    avoided. In the kq case, I chose to aquire a kq global lock before
    acquiring multiple kq locks. (In the proc case, jhb said you aquire
    the child's before the parents.)

    Mutexs have the flag MTX_DUPOK that notify witness that duplicate locks
    are ok, but this can hide other problems (and in fact would have in my
    testing).

    I have created a patch that lets you inform witness the a duplicate lock
    is valid as long as you hold another lock. The only run time change is
    that when a duplicate lock is found, it will run through another table
    to verify it's ok before printing out the back trace.

    Anyone have objections to this? 

    -- 
  John-Mark Gurney				Voice: +1 415 225 5579
     "All that I will do, has been done, All that I have, has not."

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  • Next message: Conrad J. Sabatier: "Re: install_and_reboot target for kernel's..."

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