Re: Freeing vnodes.

From: Jeff Roberson (jroberson_at_chesapeake.net)
Date: 03/29/05

  • Next message: Maxim Konovalov: "Re: Fixing DRM after phk's drive-by axeing" 
    Date: Tue, 29 Mar 2005 03:06:02 -0500 (EST)
To: David Schultz <das@FreeBSD.ORG>

    On Tue, 29 Mar 2005, David Schultz wrote:

    > On Tue, Mar 29, 2005, Jeff Roberson wrote:
    > > On Tue, 29 Mar 2005, Jeff Roberson wrote:
    > >
    > > > On Mon, 28 Mar 2005, David Schultz wrote:
    > > >
    > > > > On Mon, Mar 28, 2005, Jeff Roberson wrote:
    > > > > > > > I am worried about the v_dd,v_ddid fields of a directory B that has the
    > > > > > > > to be released vnode A as parent. (Obviously in this case there is no
    > > > > > > > namecache entry with the vnode A as the directory (nc_dvp))
    > > > > > > >
    > > > > > > > Right now A is type stable - but if A is released, access to B->v_dd
    > > > > > > > may cause a page fault.
    > > > > > > >
    > > > > > > > Stephan
    > > > > > >
    > > > > > > Jeff,
    > > > > > >
    > > > > > > Do you plan to address the problem now that the code is checked in?
    > > > > >
    > > > > > Vnodes with children in the name cache are held with vhold() and not
    > > > > > recycled.
    > > > >
    > > > > Yes, but cache_purge() is called directly in a number of places
    > > > > where the vnode may have children, e.g. in mount. So dangling
    > > > > references might still be possible unless cache_purge() fixes up
    > > > > the children's v_dd pointers appropriately.
    > > > >
    > > >
    > > > ah, indeed. How does this look:
    > >
    > > Also, are the ids really necessary now that we don't reuse vnodes?
    > > Shouldn't the pointer be sufficient?
    >
    > I think so. The patch I sent you a few days ago gets rid of v_id
    > except in vfs_cache_lookup(), where it is used to guarantee that
    > the vnode hasn't changed while sleeping in vn_lock(). With vnode
    > reclamation, that isn't safe anyway, so if you fix vfs_cache_lookup(),
    > we can kill v_id completely.

    You're right, cache_lookup() needs to be changed to return a referenced
    vnode. There are only a few callers outside of vfs_cache.c that I'll have
    to change. I'll put this on my todo list. After that v_id can go away.
    I'll look at your patch again soon.

    >
    > Your patch looks okay at a glance, but shouldn't you be iterating over
    > v_cache_src instead of v_cache_dst?
    >

    Yes, I thought I double checked that. I haven't done any name cache stuff
    in a while, and I always get confused whether src means sources for this
    vnode, or names this vnode is a source for.
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  • Next message: Maxim Konovalov: "Re: Fixing DRM after phk's drive-by axeing"

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