linux-kernel - Re: [PATCH] NFSd: fix locking in nfsd_forget

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Date:	Thu, 24 May 2012 06:56:48 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [PATCH] NFSd: fix locking in nfsd_forget_delegations()

On Thu, May 24, 2012 at 08:41:35AM +0400, Stanislav Kinsbursky wrote:
> 24.05.2012 01:31, J. Bruce Fields написал:
> >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...

Oh, blah, you're right of course.

Still, this seems a little tangled, and I'd prefer not to have to add
the useless extra parameter to break_one_deleg().

--b.

> 
> 
> >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@...allels.com>
> >>---
> >>  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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