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

[Stanislav Kinsbursky]

24.05.2012 01:31, J. Bruce Fields ÐÐÐÐÑÐÐ:
> On Tue, May 22, 2012 at 02:25:14PM +0400, Stanislav Kinsbursky wrote:
> > 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.
> All this indirection is getting a little much.
>
> How about replacing nfsd_process_n_delegations by something that always
> does the list-move?:

Is it correct?
List move is suitable for unhash delegations since we anyway remove 
delegation from fi_delegations list.
But seems we don't do this for delegations recall...


> void nfsd_forget_delegations(u64 num)
> {
> 	unsigned int count;
> 	list_head victims;
>
> 	nfs4_lock_state();
> 	count = nfsd_get_n_delegations(num,&victims);
> 	list_for_each_entry_safe(...,&victims, ...)
> 		unhash_delegation();
> 	unlock_state();
> }
>
> ditto for recall_delegations, and take the recall_lock inside
> nfsd_get_n_delegations?
>
> Or something like that.
>
> --b.
>
> > Signed-off-by: Stanislav Kinsbursky<skinsbursky@xxxxxxxxxxxxx>
> > ---
> >   fs/nfsd/nfs4state.c |   32 ++++++++++++++++++++++++--------
> >   1 files changed, 24 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > index 21266c7..f004e61 100644
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -2597,7 +2597,7 @@ out:
> >   	return ret;
> >   }
> >
> > -static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
> > +static void nfsd_break_one_deleg(struct nfs4_delegation *dp, void *data)
> >   {
> >   	/* We're assuming the state code never drops its reference
> >   	 * without first removing the lease.  Since we're in this lease
> > @@ -2633,7 +2633,7 @@ static void nfsd_break_deleg_cb(struct file_lock *fl)
> >   	spin_lock(&recall_lock);
> >   	fp->fi_had_conflict = true;
> >   	list_for_each_entry(dp,&fp->fi_delegations, dl_perfile)
> > -		nfsd_break_one_deleg(dp);
> > +		nfsd_break_one_deleg(dp, NULL);
> >   	spin_unlock(&recall_lock);
> >   }
> >
> > @@ -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, void (*deleg_func)(struct nfs4_delegation *, void *), void *data)
> >   {
> >   	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);
> > +				deleg_func(dp, data);
> >   				if (++count == num)
> >   					return count;
> >   			}
> > @@ -4713,15 +4713,31 @@ int nfsd_process_n_delegations(u64 num, void (*deleg_func)(struct nfs4_delegatio
> >   	return count;
> >   }
> >
> > +/* Called under the recall_lock spinlock. */
> > +static void
> > +collect_delegation(struct nfs4_delegation *dp, void *data)
> > +{
> > +	struct list_head *list = data;
> > +
> > +	list_move(&dp->dl_perfile, list);
> > +}
> > +
> >   void nfsd_forget_delegations(u64 num)
> >   {
> >   	unsigned int count;
> > +	struct nfs4_delegation *dp, *dnext;
> > +	LIST_HEAD(unhash_list);
> >
> > -	nfs4_lock_state();
> > -	count = nfsd_process_n_delegations(num, unhash_delegation);
> > -	nfs4_unlock_state();
> > +	spin_lock(&recall_lock);
> > +	count = nfsd_process_n_delegations(num, collect_delegation,&unhash_list);
> > +	spin_unlock(&recall_lock);
> >
> >   	printk(KERN_INFO "NFSD: Forgot %d delegations", count);
> > +
> > +	nfs4_lock_state();
> > +	list_for_each_entry_safe(dp, dnext,&unhash_list, dl_perfile)
> > +		unhash_delegation(dp);
> > +	nfs4_unlock_state();
> >   }
> >
> >   void nfsd_recall_delegations(u64 num)
> > @@ -4730,7 +4746,7 @@ void nfsd_recall_delegations(u64 num)
> >
> >   	nfs4_lock_state();
> >   	spin_lock(&recall_lock);
> > -	count = nfsd_process_n_delegations(num, nfsd_break_one_deleg);
> > +	count = nfsd_process_n_delegations(num, nfsd_break_one_deleg, NULL);
> >   	spin_unlock(&recall_lock);
> >   	nfs4_unlock_state();

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