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Date:   Fri, 21 May 2021 16:23:14 -0400
From:   "bfields@fieldses.org" <bfields@fieldses.org>
To:     Trond Myklebust <trondmy@hammerspace.com>
Cc:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH 1/4] NFSv4: Fix delegation return in cases where we have
 to retry
Message-ID: <20210521202314.GD30314@fieldses.org>
References: <20210520163902.215745-1-trondmy@kernel.org>
 <20210520163902.215745-2-trondmy@kernel.org>
 <20210520182901.GA8759@fieldses.org>
 <2b24ca81205cca400910bbbdc29d54aafccefe00.camel@hammerspace.com>
 <20210520204719.GB10415@fieldses.org>
 <de87f0b97508acce0736cd3c4bfe2dac9cbb29b7.camel@hammerspace.com>
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On Thu, May 20, 2021 at 09:14:09PM +0000, Trond Myklebust wrote:
> On Thu, 2021-05-20 at 16:47 -0400, bfields@fieldses.org wrote:
> > On Thu, May 20, 2021 at 07:08:24PM +0000, Trond Myklebust wrote:
> > > On Thu, 2021-05-20 at 14:29 -0400, J. Bruce Fields wrote:
> > > > On Thu, May 20, 2021 at 12:38:59PM -0400, trondmy@kernel.org wrote:
> > > > > From: Trond Myklebust <trond.myklebust@hammerspace.com>
> > > > > 
> > > > > If we're unable to immediately recover all locks because the
> > > > > server
> > > > > is
> > > > > unable to immediately service our reclaim calls, then we want to
> > > > > retry
> > > > > after we've finished servicing all the other asynchronous
> > > > > delegation
> > > > > returns on our queue.
> > > > 
> > > > So, there's a situation where the server can't service a reclaim
> > > > until
> > > > some other delegation is returned?  I'm not seeing how that
> > > > happens.
> > > > 
> > > 
> > > I can and I do... pNFS can be complicated...
> > 
> > I don't doubt you, but does everyone get this but me?
> > 
> > Is it too complicated to explain?
> > 
> 
> Not if you read the code, no.

I tried, and couldn't follow it, at least not on a quick read.

It's OK, I guess, it was mainly just curiosity.

--b.

> 
> In nfs_end_delegation_return():
> 
>         do {
>                 if (test_bit(NFS_DELEGATION_REVOKED, &delegation->flags))
>                         break;
>                 err = nfs_delegation_claim_opens(inode, &delegation->stateid,
>                                 delegation->type);
>                 if (!issync || err != -EAGAIN)
>                         break;
>                 /*
>                  * Guard against state recovery
>                  */
>                 err = nfs4_wait_clnt_recover(clp);
>         } while (err == 0);
> 
> So if issync is false, then we abort the delegation return and try
> again later.
> 
> ...and when we later add a break_lease() call in this patch series,
> then there is another condition.
> 
> > --b.
> > 
> > > 
> > > > --b.
> > > > 
> > > > > 
> > > > > Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> > > > > ---
> > > > >  fs/nfs/delegation.c | 71 +++++++++++++++++++++++++++++++++++----
> > > > > --
> > > > > ----
> > > > >  fs/nfs/delegation.h |  1 +
> > > > >  fs/nfs/nfs4_fs.h    |  1 +
> > > > >  3 files changed, 58 insertions(+), 15 deletions(-)
> > > > > 
> > > > > diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
> > > > > index e6ec6f09ac6e..7c45ac3c3b0b 100644
> > > > > --- a/fs/nfs/delegation.c
> > > > > +++ b/fs/nfs/delegation.c
> > > > > @@ -75,6 +75,13 @@ void nfs_mark_delegation_referenced(struct
> > > > > nfs_delegation *delegation)
> > > > >         set_bit(NFS_DELEGATION_REFERENCED, &delegation->flags);
> > > > >  }
> > > > >  
> > > > > +static void nfs_mark_return_delegation(struct nfs_server
> > > > > *server,
> > > > > +                                      struct nfs_delegation
> > > > > *delegation)
> > > > > +{
> > > > > +       set_bit(NFS_DELEGATION_RETURN, &delegation->flags);
> > > > > +       set_bit(NFS4CLNT_DELEGRETURN, &server->nfs_client-
> > > > > > cl_state);
> > > > > +}
> > > > > +
> > > > >  static bool
> > > > >  nfs4_is_valid_delegation(const struct nfs_delegation
> > > > > *delegation,
> > > > >                 fmode_t flags)
> > > > > @@ -293,6 +300,7 @@ nfs_start_delegation_return_locked(struct
> > > > > nfs_inode *nfsi)
> > > > >                 goto out;
> > > > >         spin_lock(&delegation->lock);
> > > > >         if (!test_and_set_bit(NFS_DELEGATION_RETURNING,
> > > > > &delegation->flags)) {
> > > > > +               clear_bit(NFS_DELEGATION_RETURN_DELAYED,
> > > > > &delegation->flags);
> > > > >                 /* Refcount matched in
> > > > > nfs_end_delegation_return()
> > > > > */
> > > > >                 ret = nfs_get_delegation(delegation);
> > > > >         }
> > > > > @@ -314,16 +322,17 @@ nfs_start_delegation_return(struct
> > > > > nfs_inode
> > > > > *nfsi)
> > > > >         return delegation;
> > > > >  }
> > > > >  
> > > > > -static void
> > > > > -nfs_abort_delegation_return(struct nfs_delegation *delegation,
> > > > > -               struct nfs_client *clp)
> > > > > +static void nfs_abort_delegation_return(struct nfs_delegation
> > > > > *delegation,
> > > > > +                                       struct nfs_client *clp,
> > > > > int
> > > > > err)
> > > > >  {
> > > > >  
> > > > >         spin_lock(&delegation->lock);
> > > > >         clear_bit(NFS_DELEGATION_RETURNING, &delegation->flags);
> > > > > -       set_bit(NFS_DELEGATION_RETURN, &delegation->flags);
> > > > > +       if (err == -EAGAIN) {
> > > > > +               set_bit(NFS_DELEGATION_RETURN_DELAYED,
> > > > > &delegation-
> > > > > > flags);
> > > > > +               set_bit(NFS4CLNT_DELEGRETURN_DELAYED, &clp-
> > > > > > cl_state);
> > > > > +       }
> > > > >         spin_unlock(&delegation->lock);
> > > > > -       set_bit(NFS4CLNT_DELEGRETURN, &clp->cl_state);
> > > > >  }
> > > > >  
> > > > >  static struct nfs_delegation *
> > > > > @@ -539,7 +548,7 @@ static int nfs_end_delegation_return(struct
> > > > > inode *inode, struct nfs_delegation
> > > > >         } while (err == 0);
> > > > >  
> > > > >         if (err) {
> > > > > -               nfs_abort_delegation_return(delegation, clp);
> > > > > +               nfs_abort_delegation_return(delegation, clp,
> > > > > err);
> > > > >                 goto out;
> > > > >         }
> > > > >  
> > > > > @@ -568,6 +577,7 @@ static bool nfs_delegation_need_return(struct
> > > > > nfs_delegation *delegation)
> > > > >         if (ret)
> > > > >                 clear_bit(NFS_DELEGATION_RETURN_IF_CLOSED,
> > > > > &delegation->flags);
> > > > >         if (test_bit(NFS_DELEGATION_RETURNING, &delegation-
> > > > > >flags)
> > > > > > > 
> > > > > +           test_bit(NFS_DELEGATION_RETURN_DELAYED, &delegation-
> > > > > > flags) ||
> > > > >             test_bit(NFS_DELEGATION_REVOKED, &delegation->flags))
> > > > >                 ret = false;
> > > > >  
> > > > > @@ -647,6 +657,38 @@ static int
> > > > > nfs_server_return_marked_delegations(struct nfs_server *server,
> > > > >         return err;
> > > > >  }
> > > > >  
> > > > > +static bool nfs_server_clear_delayed_delegations(struct
> > > > > nfs_server
> > > > > *server)
> > > > > +{
> > > > > +       struct nfs_delegation *d;
> > > > > +       bool ret = false;
> > > > > +
> > > > > +       list_for_each_entry_rcu (d, &server->delegations,
> > > > > super_list) {
> > > > > +               if (!test_bit(NFS_DELEGATION_RETURN_DELAYED, &d-
> > > > > > flags))
> > > > > +                       continue;
> > > > > +               nfs_mark_return_delegation(server, d);
> > > > > +               clear_bit(NFS_DELEGATION_RETURN_DELAYED, &d-
> > > > > > flags);
> > > > > +               ret = true;
> > > > > +       }
> > > > > +       return ret;
> > > > > +}
> > > > > +
> > > > > +static bool nfs_client_clear_delayed_delegations(struct
> > > > > nfs_client
> > > > > *clp)
> > > > > +{
> > > > > +       struct nfs_server *server;
> > > > > +       bool ret = false;
> > > > > +
> > > > > +       if (!test_and_clear_bit(NFS4CLNT_DELEGRETURN_DELAYED,
> > > > > &clp-
> > > > > > cl_state))
> > > > > +               goto out;
> > > > > +       rcu_read_lock();
> > > > > +       list_for_each_entry_rcu (server, &clp->cl_superblocks,
> > > > > client_link) {
> > > > > +               if (nfs_server_clear_delayed_delegations(server))
> > > > > +                       ret = true;
> > > > > +       }
> > > > > +       rcu_read_unlock();
> > > > > +out:
> > > > > +       return ret;
> > > > > +}
> > > > > +
> > > > >  /**
> > > > >   * nfs_client_return_marked_delegations - return previously
> > > > > marked
> > > > > delegations
> > > > >   * @clp: nfs_client to process
> > > > > @@ -659,8 +701,14 @@ static int
> > > > > nfs_server_return_marked_delegations(struct nfs_server *server,
> > > > >   */
> > > > >  int nfs_client_return_marked_delegations(struct nfs_client *clp)
> > > > >  {
> > > > > -       return nfs_client_for_each_server(clp,
> > > > > -                       nfs_server_return_marked_delegations,
> > > > > NULL);
> > > > > +       int err = nfs_client_for_each_server(
> > > > > +               clp, nfs_server_return_marked_delegations, NULL);
> > > > > +       if (err)
> > > > > +               return err;
> > > > > +       /* If a return was delayed, sleep to prevent hard looping
> > > > > */
> > > > > +       if (nfs_client_clear_delayed_delegations(clp))
> > > > > +               ssleep(1);
> > > > > +       return 0;
> > > > >  }
> > > > >  
> > > > >  /**
> > > > > @@ -775,13 +823,6 @@ static void
> > > > > nfs_mark_return_if_closed_delegation(struct nfs_server *server,
> > > > >         set_bit(NFS4CLNT_DELEGRETURN, &server->nfs_client-
> > > > > > cl_state);
> > > > >  }
> > > > >  
> > > > > -static void nfs_mark_return_delegation(struct nfs_server
> > > > > *server,
> > > > > -               struct nfs_delegation *delegation)
> > > > > -{
> > > > > -       set_bit(NFS_DELEGATION_RETURN, &delegation->flags);
> > > > > -       set_bit(NFS4CLNT_DELEGRETURN, &server->nfs_client-
> > > > > > cl_state);
> > > > > -}
> > > > > -
> > > > >  static bool nfs_server_mark_return_all_delegations(struct
> > > > > nfs_server *server)
> > > > >  {
> > > > >         struct nfs_delegation *delegation;
> > > > > diff --git a/fs/nfs/delegation.h b/fs/nfs/delegation.h
> > > > > index c19b4fd20781..1c378992b7c0 100644
> > > > > --- a/fs/nfs/delegation.h
> > > > > +++ b/fs/nfs/delegation.h
> > > > > @@ -36,6 +36,7 @@ enum {
> > > > >         NFS_DELEGATION_REVOKED,
> > > > >         NFS_DELEGATION_TEST_EXPIRED,
> > > > >         NFS_DELEGATION_INODE_FREEING,
> > > > > +       NFS_DELEGATION_RETURN_DELAYED,
> > > > >  };
> > > > >  
> > > > >  int nfs_inode_set_delegation(struct inode *inode, const struct
> > > > > cred *cred,
> > > > > diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
> > > > > index 065cb04222a1..4c44322c2643 100644
> > > > > --- a/fs/nfs/nfs4_fs.h
> > > > > +++ b/fs/nfs/nfs4_fs.h
> > > > > @@ -45,6 +45,7 @@ enum nfs4_client_state {
> > > > >         NFS4CLNT_RECALL_RUNNING,
> > > > >         NFS4CLNT_RECALL_ANY_LAYOUT_READ,
> > > > >         NFS4CLNT_RECALL_ANY_LAYOUT_RW,
> > > > > +       NFS4CLNT_DELEGRETURN_DELAYED,
> > > > >  };
> > > > >  
> > > > >  #define NFS4_RENEW_TIMEOUT             0x01
> > > > > -- 
> > > > > 2.31.1
> > > 
> > > -- 
> > > Trond Myklebust
> > > Linux NFS client maintainer, Hammerspace
> > > trond.myklebust@hammerspace.com
> > > 
> > > 
> 
> -- 
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com
> 
>