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);
>> 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;
>>
--
William
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