Re: [9fans] clunk clunk

[Bruce Ellis <bruce.ellis@gmail.com>]

Bullshit.  It happens all the time.  Rio+Plumber is a simple example.

brucee

On 1/4/06, Russ Cox <rsc@swtch.com> wrote:
> > When a process exits it closes it's fds, so it sends a
> > Tclunk ...but if the process it sends it to is exiting it can't
> > respond.   It's in the same position.  Call it "deadly embrace".
> >
> > Think about it.
>
> This only happens if two file servers have mounted each other,
> which creates many other possibilities for deadlock too.
>
> Usually file servers are careful to dissociate from the name
> spaces in which they mount themselves, so that they don't
> access their own files and cause ref count problems.
> This has the added effect that future servers that get mounted
> into the name space don't end up mounted in the first server's
> name space.  So these kind of loops basically don't happen.
>
> What processes do you have running that are in this deadly
> embrace?  Standard programs or ones you wrote?  If the
> former, which ones?  Are you sure they're in Tclunk?
>
> There is one exception in Plan 9: upas/fs and plumber have
> each other mounted, so that plumber can send around
> references to upas/fs's files.  It sometimes happens that
> they end up sticking around just because of the circular
> ref count, if somehow the session ends without a hangup
> note being sent to the note group.  Even in this case, though,
> the Tclunk thing doesn't happen, because plumber doesn't
> keep any of upas/fs's files open.  It could possibly happen
> if the plumber managed to get killed in the middle of walking
> one of the upas paths during a stat, but that wouldn't happen
> hundreds of times on a single system.
>
> Instead of making us read through the Inferno code,
> why not tell us what you did to fix it?  A separate kproc
> to run all clunks?  Close all the non-devmnt chans first?
>
> Russ
>