Return-Path: Received: from mx142.netapp.com ([216.240.21.19]:17009 "EHLO mx142.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752159AbcD1RWa (ORCPT ); Thu, 28 Apr 2016 13:22:30 -0400 From: Anna Schumaker Subject: Re: [PATCH] NFS: Fix an LOCK/OPEN race when unlinking an open file To: Chuck Lever , Olga Kornievskaia References: <20160411201733.20911.86904.stgit@manet.1015granger.net> <7655D216-7C44-41A6-A6BC-BD5E91E5FDB6@oracle.com> CC: Anna Schumaker , William Dauchy , Trond Myklebust , Linux NFS Mailing List Message-ID: <7ae5ae32-7721-fa8e-9b07-e7b705f85863@Netapp.com> Date: Thu, 28 Apr 2016 13:22:23 -0400 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Sender: linux-nfs-owner@vger.kernel.org List-ID: On 04/28/2016 12:05 PM, Chuck Lever wrote: > >> On Apr 28, 2016, at 11:56 AM, Olga Kornievskaia wrote: >> >> 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). > > Anna's choice. Sounds like a good idea. Is there any particular wording that you want? If not, then I can try to base something off of your email from Tuesday (4/26). Anna > > >> 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 >>>> >>>> >>>> >>> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > Chuck Lever > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >