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Date:   Mon, 25 Apr 2022 12:17:22 -0400
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Dai Ngo <dai.ngo@oracle.com>
Cc:     chuck.lever@oracle.com, jlayton@redhat.com,
        viro@zeniv.linux.org.uk, linux-nfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH RFC v21 0/7] NFSD: Initial implementation of NFSv4
 Courteous Server
Message-ID: <20220425161722.GC24825@fieldses.org>
References: <1650739455-26096-1-git-send-email-dai.ngo@oracle.com>
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On Sat, Apr 23, 2022 at 11:44:08AM -0700, Dai Ngo wrote:
> . Redo based on Bruce's suggestion by breaking the patches into functionality
>   and also don't remove client record of courtesy client until the client is
>   actually expired.
> 
>   0001: courteous server framework with support for client with delegation only.
>         This patch also handles COURTESY and EXPIRABLE reconnect.
>         Conflict is resolved by set the courtesy client to EXPIRABLE, let the
>         laundromat expires the client on next run and return NFS4ERR_DELAY
>         OPEN request.
> 
>   0002: add support for opens/share reservation to courteous server
>         Conflict is resolved by set the courtesy client to EXPIRABLE, let the
>         laundromat expires the client on next run and return NFS4ERR_DELAY
>         OPEN request.
> 
>   0003: mv creation/destroying laundromat workqueue from nfs4_state_start and
>         and nfs4_state_shutdown_net to init_nfsd and exit_nfsd.
> 
>   0004: fs/lock: add locks_owner_has_blockers helper
>   
>   0005: add 2 callbacks to lock_manager_operations for resolving lock conflict
>   
>   0006: add support for locks to courteous server, making use of 0004 and 0005
>         Conflict is resolved by set the courtesy client to EXPIRABLE, run the
>         laundromat immediately and wait for it to complete before returning to
>         fs/lock code to recheck the lock list from the beginning.
> 
>         NOTE: I could not get queue_work/queue_delay_work and flush_workqueue
>         to work as expected, I have to use mod_delayed_work and flush_workqueue
>         to get the laundromat to run immediately.

Whoops, yes, my bad.

>         When we check for blockers in nfs4_anylock_blockers, we do not check
>         for client with delegation conflict. This is because we already hold
>         the client_lock and to check for delegation conflict we need the state_lock
>         and scanning the del_recall_lru list each time. So to avoid this overhead
>         and potential deadlock (not sure about lock of ordering of these locks)
>         we check and set the COURTESY client with delegation being recalled to
>         EXPIRABLE later in nfs4_laundromat.

Hm, OK, I'll think about that, but sounds like it should work.

--b.

> 
>   0007: show state of courtesy client in client info.