[Devel] Re: [PATCH v2] NFSd: fix locking in nfsd_forget_delegations()

[J. Bruce Fields]

On Fri, May 25, 2012 at 06:38:50PM +0400, Stanislav Kinsbursky wrote:
> v2: dl_recall_lru list is used for delegations collect because it's modified
> both in unhash_delegation() and nfsd_break_one_deleg().
> 
> This patch adds recall_lock hold to nfsd_forget_delegations() to protect
> nfsd_process_n_delegations() call.
> Also, looks like it would be better to collect delegations to some local
> on-stack list, and then unhash collected list. This split allows to
> simplify locking, because delegation traversing is protected by recall_lock,
> when delegation unhash is protected by client_mutex.

Thanks, applying for 3.6 (assuming Bryan doesn't have any objection).

--b.

> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky at parallels.com>
> ---
>  fs/nfsd/nfs4state.c |   21 +++++++++++++++++----
>  1 files changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 21266c7..3d6848b 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -4694,7 +4694,7 @@ void nfsd_forget_openowners(u64 num)
>  	printk(KERN_INFO "NFSD: Forgot %d open owners", count);
>  }
>  
> -int nfsd_process_n_delegations(u64 num, void (*deleg_func)(struct nfs4_delegation *))
> +int nfsd_process_n_delegations(u64 num, struct list_head *list)
>  {
>  	int i, count = 0;
>  	struct nfs4_file *fp, *fnext;
> @@ -4703,7 +4703,7 @@ int nfsd_process_n_delegations(u64 num, void (*deleg_func)(struct nfs4_delegatio
>  	for (i = 0; i < FILE_HASH_SIZE; i++) {
>  		list_for_each_entry_safe(fp, fnext, &file_hashtbl[i], fi_hash) {
>  			list_for_each_entry_safe(dp, dnext, &fp->fi_delegations, dl_perfile) {
> -				deleg_func(dp);
> +				list_move(&dp->dl_recall_lru, list);
>  				if (++count == num)
>  					return count;
>  			}
> @@ -4716,9 +4716,16 @@ int nfsd_process_n_delegations(u64 num, void (*deleg_func)(struct nfs4_delegatio
>  void nfsd_forget_delegations(u64 num)
>  {
>  	unsigned int count;
> +	LIST_HEAD(victims);
> +	struct nfs4_delegation *dp, *dnext;
> +
> +	spin_lock(&recall_lock);
> +	count = nfsd_process_n_delegations(num, &victims);
> +	spin_unlock(&recall_lock);
>  
>  	nfs4_lock_state();
> -	count = nfsd_process_n_delegations(num, unhash_delegation);
> +	list_for_each_entry_safe(dp, dnext, &victims, dl_recall_lru)
> +		unhash_delegation(dp);
>  	nfs4_unlock_state();
>  
>  	printk(KERN_INFO "NFSD: Forgot %d delegations", count);
> @@ -4727,10 +4734,16 @@ void nfsd_forget_delegations(u64 num)
>  void nfsd_recall_delegations(u64 num)
>  {
>  	unsigned int count;
> +	LIST_HEAD(victims);
> +	struct nfs4_delegation *dp, *dnext;
>  
>  	nfs4_lock_state();
>  	spin_lock(&recall_lock);
> -	count = nfsd_process_n_delegations(num, nfsd_break_one_deleg);
> +	count = nfsd_process_n_delegations(num, &victims);
> +	list_for_each_entry_safe(dp, dnext, &victims, dl_recall_lru) {
> +		list_del(&dp->dl_recall_lru);
> +		nfsd_break_one_deleg(dp);
> +	}
>  	spin_unlock(&recall_lock);
>  	nfs4_unlock_state();
>  
> 
> --
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