> On Apr 28, 2016, at 9:13 AM, Anna Schumaker <Anna.Schumaker@xxxxxxxxxx> 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 <aglo@xxxxxxxxx> 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 <chuck.lever@xxxxxxxxxx> 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 <chuck.lever@xxxxxxxxxx>
>>>> ---
>>>> 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
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