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List:       freebsd-stable
Subject:    Re: nfs_fsync: not dirty  error in 4.5-RELEASE (possible solution)
From:       Matthew Dillon <dillon () apollo ! backplane ! com>
Date:       2002-03-29 22:34:51
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    Ok, I am putting this back on the main list.

    After looking at a kernel core that Danny graciously provided, I believe
    I have located the problem.

    The core shows NFS panicing on a struct buf showing up on the vnode's 
    v_dirtyblkhd list that is not marked B_DELWRI.

    After examining the core I found that the buffer was marked B_INVAL,
    and I found a case in brelse() where B_DELWRI is cleared on a buffer
    marked B_DELWRI|B_INVAL without moving it out of the vnode's v_dirtyblkhd
    list.  Specifically, line 1214 if kern/vfs_bio.c:

        /*
         * If B_INVAL, clear B_DELWRI.  We've already placed the buffer
         * on the correct queue.
         */
        if ((bp->b_flags & (B_INVAL|B_DELWRI)) == (B_INVAL|B_DELWRI)) {
                bp->b_flags &= ~B_DELWRI;
                --numdirtybuffers;
                numdirtywakeup(lodirtybuffers);
        }               

    I believe that the correct fix is to change this code to:
    
        /*
         * If B_INVAL, clear B_DELWRI.  We've already placed the buffer
         * on the correct queue.
         */
        if ((bp->b_flags & (B_INVAL|B_DELWRI)) == (B_INVAL|B_DELWRI))
		bundirty(bp);

    I would appreciate it if everyone who is able to easily reproduce this
    panic would test this fix and post your results back to the list.  If
    this solves the problem I will commit it to -current and -stable.

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>

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