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
<Anna.Schumaker@xxxxxxxxxx> wrote:
> On 04/28/2016 10:06 AM, Chuck Lever wrote:
>>
>>> 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.
>
> 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@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
