Return-Path: Received: from mail-io0-f194.google.com ([209.85.223.194]:33524 "EHLO mail-io0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753120AbcD1P4K (ORCPT ); Thu, 28 Apr 2016 11:56:10 -0400 Received: by mail-io0-f194.google.com with SMTP id x35so12610930ioi.0 for ; Thu, 28 Apr 2016 08:56:09 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <20160411201733.20911.86904.stgit@manet.1015granger.net> <7655D216-7C44-41A6-A6BC-BD5E91E5FDB6@oracle.com> Date: Thu, 28 Apr 2016 11:56:08 -0400 Message-ID: Subject: Re: [PATCH] NFS: Fix an LOCK/OPEN race when unlinking an open file From: Olga Kornievskaia To: Anna Schumaker Cc: Chuck Lever , William Dauchy , Trond Myklebust , Linux NFS Mailing List Content-Type: text/plain; charset=UTF-8 Sender: linux-nfs-owner@vger.kernel.org List-ID: Chuck or Anna, If the patch is accepted, do you mind expanding the commit message to include the wording about the LOCK and CB_RECALL race (so that it's documented to look back into it). On Thu, Apr 28, 2016 at 10:09 AM, Anna Schumaker wrote: > On 04/28/2016 10:06 AM, Chuck Lever wrote: >> >>> 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. > > Got it. Thanks for checking! > > Anna > >> >> >>> 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 >> >> >> >