Re: [PATCH v2] nfsd: Don't release the callback slot unless it was actually held

[Trond Myklebust <trondmy@hammerspace.com>]

On Fri, 2019-04-05 at 08:54 -0700, Trond Myklebust wrote:
> If there are multiple callbacks queued, waiting for the callback
> slot when the callback gets shut down, then they all currently
> end up acting as if they hold the slot, and call
> nfsd4_cb_sequence_done() resulting in interesting side-effects.
> 
> In addition, the 'retry_nowait' path in nfsd4_cb_sequence_done()
> causes a loop back to nfsd4_cb_prepare() without first freeing the
> slot, which causes a deadlock when nfsd41_cb_get_slot() gets called
> a second time.
> 
> This patch therefore adds a boolean to track whether or not the
> callback did pick up the slot, so that it can do the right thing
> in these 2 cases.
> 
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> ---
> v2: try to restart the callback if we hit nfsd4_cb_sequence_done()
>     without a slot.
> 
> 

Hi Bruce,

Should this patch perhaps be considered for stable? The callback slot
leak is permanent (or at least for the lifetime of the nfs4_client).

Cheers
  Trond

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com