Return-Path: Received: from aserp1040.oracle.com ([141.146.126.69]:30017 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750932AbcD1OHG convert rfc822-to-8bit (ORCPT ); Thu, 28 Apr 2016 10:07:06 -0400 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Subject: Re: [PATCH] NFS: Fix an LOCK/OPEN race when unlinking an open file From: Chuck Lever In-Reply-To: Date: Thu, 28 Apr 2016 10:06:54 -0400 Cc: William Dauchy , Trond Myklebust , Linux NFS Mailing List , Olga Kornievskaia Message-Id: <7655D216-7C44-41A6-A6BC-BD5E91E5FDB6@oracle.com> References: <20160411201733.20911.86904.stgit@manet.1015granger.net> To: Anna Schumaker Sender: linux-nfs-owner@vger.kernel.org List-ID: > On Apr 28, 2016, at 9:13 AM, Anna Schumaker wrote: > > The patch looks pretty straightforward to me, and it sounds like it fixes a few problems that people are seeing. One question (below): > > On 04/28/2016 08:43 AM, William Dauchy wrote: >> Hello Anna, >> >> Could you have a look at this one please? >> >> Thanks, >> >> William >> >> On Tue, Apr 26, 2016 at 4:24 PM, Olga Kornievskaia wrote: >>> I believe this patch also helps with a race between a LOCK and >>> CB_RECALL. Application does a lock as the delegation is being >>> recalled. The lock thread sees the delegated state and acquires a >>> local lock. At the same time delegation doesn't see it the lock yet >>> and returns the delegation. Application proceeds to do IO. It ends up >>> using an open stateid for the IO (as there is no delegation stateid or >>> lock stateid). The server is unaware of the lock so it can give that >>> lock to somebody else. Yet this client thinks it has a local lock. It >>> leads to inconsistent data between clients. >>> >>> On Mon, Apr 11, 2016 at 4:20 PM, Chuck Lever wrote: >>>> At Connectathon 2016, we found that recent upstream Linux clients >>>> would occasionally send a LOCK operation with a zero stateid. This >>>> appeared to happen in close proximity to another thread returning >>>> a delegation before unlinking the same file while it remained open. >>>> >>>> Earlier, the client received a write delegation on this file and >>>> returned the open stateid. Now, as it is getting ready to unlink the >>>> file, it returns the write delegation. But there is still an open >>>> file descriptor on that file, so the client must OPEN the file >>>> again before it returns the delegation. >>>> >>>> Since commit 24311f884189 ('NFSv4: Recovery of recalled read >>>> delegations is broken'), nfs_open_delegation_recall() clears the >>>> NFS_DELEGATED_STATE flag _before_ it sends the OPEN. This allows a >>>> racing LOCK on the same inode to be put on the wire before the OPEN >>>> operation has returned a valid open stateid. >>>> >>>> To eliminate this race, serialize delegation return with the >>>> acquisition of a file lock on the same file. Adopt the same approach >>>> as is used in the unlock path. >>>> >>>> Fixes: 24311f884189 ('NFSv4: Recovery of recalled read ... ') >>>> Signed-off-by: Chuck Lever >>>> --- >>>> Hi- >>>> >>>> This fix appears to be both safe and effective. Please consider >>>> it for v4.7 and for stable. Thanks! >>>> >>>> >>>> fs/nfs/nfs4proc.c | 4 ++++ >>>> 1 file changed, 4 insertions(+) >>>> >>>> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c >>>> index 01bef06..c40f1b6 100644 >>>> --- a/fs/nfs/nfs4proc.c >>>> +++ b/fs/nfs/nfs4proc.c >>>> @@ -6054,6 +6054,7 @@ static int nfs41_lock_expired(struct nfs4_state *state, struct file_lock *reques >>>> static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock *request) >>>> { >>>> struct nfs_inode *nfsi = NFS_I(state->inode); >>>> + struct nfs4_state_owner *sp = state->owner; >>>> unsigned char fl_flags = request->fl_flags; >>>> int status = -ENOLCK; >>>> >>>> @@ -6068,6 +6069,7 @@ static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock >>>> status = do_vfs_lock(state->inode, request); >>>> if (status < 0) >>>> goto out; >>>> + mutex_lock(&sp->so_delegreturn_mutex); > > From what I can tell, the first call to do_vfs_lock() in this function is used to test if we can take the lock locally. Do we need to worry about this racing with delegreturn, too? When I included that call in the critical section, cthon04 locking tests deadlocked. > Thanks, > Anna > >>>> down_read(&nfsi->rwsem); >>>> if (test_bit(NFS_DELEGATED_STATE, &state->flags)) { >>>> /* Yes: cache locks! */ >>>> @@ -6075,9 +6077,11 @@ static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock >>>> request->fl_flags = fl_flags & ~FL_SLEEP; >>>> status = do_vfs_lock(state->inode, request); >>>> up_read(&nfsi->rwsem); >>>> + mutex_unlock(&sp->so_delegreturn_mutex); >>>> goto out; >>>> } >>>> up_read(&nfsi->rwsem); >>>> + mutex_unlock(&sp->so_delegreturn_mutex); >>>> status = _nfs4_do_setlk(state, cmd, request, NFS_LOCK_NEW); >>>> out: >>>> request->fl_flags = fl_flags; -- Chuck Lever