linux-kernel - Re: [PATCH] nfsd4: remove state lock from nfs4_state

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Message-ID: <20121127221105.GJ27142@fieldses.org>
Date:	Tue, 27 Nov 2012 17:11:05 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	linux-nfs@...r.kernel.org, Trond.Myklebust@...app.com,
	linux-kernel@...r.kernel.org, devel@...nvz.org
Subject: Re: [PATCH] nfsd4: remove state lock from nfs4_state_shutdown

OK, applying.--b.

On Wed, Nov 21, 2012 at 06:07:38PM +0300, Stanislav Kinsbursky wrote:
> Protection of __nfs4_state_shutdown() with nfs4_lock_state() looks redundant.
> 
> This function is called by the last NFSd thread on it's exit and state lock
> protects actually two functions (del_recall_lru is protected by recall_lock):
> 1) nfsd4_client_tracking_exit
> 2) __nfs4_state_shutdown_net
> 
> "nfsd4_client_tracking_exit" doesn't require state lock protection, because it's
> state can be modified only by tracker callbacks.
> Here a re they:
> 1) create: is called only from nfsd4_proc_compound.
> 2) remove: is called from either nfsd4_proc_compound or nfs4_laundromat.
> 3) check: is called only from nfsd4_proc_compound.
> 4) grace_done; called only from nfs4_laundromat.
> 
> nfsd4_proc_compound is called onll by NFSd kthread, which is exiting right
> now.
> nfs4_laundromat is called by laundry_wq. But laundromat_work was canceled
> already.
> 
> "__nfs4_state_shutdown_net" also doesn't require state lock protection,
> because all NFSd kthreads are dead, and no race can happen with NFSd start,
> because "nfsd_up" flag is still set.
> Moreover, all Nfsd shutdown is protected with global nfsd_mutex.
> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
> ---
>  fs/nfsd/nfs4state.c |    2 --
>  1 files changed, 0 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index e75872f..d41cc71 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -4926,9 +4926,7 @@ nfs4_state_shutdown(void)
>  	cancel_delayed_work_sync(&nn->laundromat_work);
>  	destroy_workqueue(laundry_wq);
>  	locks_end_grace(&nn->nfsd4_manager);
> -	nfs4_lock_state();
>  	__nfs4_state_shutdown(net);
> -	nfs4_unlock_state();
>  	nfsd4_destroy_callback_queue();
>  }
>  
> 
--
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