Re: [PATCH v2 1/2] nfsd: wake waiters blocked on file_lock before deleting it

[Steve Dickson <SteveD@RedHat.com>]

On 4/24/19 9:58 AM, J. Bruce Fields wrote:
> Steve, see Neil's comment, is there a cifs bug here?
Looking into it... 

steved.
> 
> --b.
> 
> On Tue, Apr 23, 2019 at 09:47:06AM +1000, NeilBrown wrote:
>> On Mon, Apr 22 2019, Jeff Layton wrote:
>>
>>> After a blocked nfsd file_lock request is deleted, knfsd will send a
>>> callback to the client and then free the request. Commit 16306a61d3b7
>>> ("fs/locks: always delete_block after waiting.") changed it such that
>>> locks_delete_block is always called on a request after it is awoken,
>>> but that patch missed fixing up blocked nfsd request handling.
>>>
>>> Call locks_delete_block on the block to wake up any locks still blocked
>>> on the nfsd lock request before freeing it. Some of its callers already
>>> do this however, so just remove those calls.
>>>
>>> URL: https://bugzilla.kernel.org/show_bug.cgi?id=203363
>>> Fixes: 16306a61d3b7 ("fs/locks: always delete_block after waiting.")
>>> Reported-by: Slawomir Pryczek <slawek1211@gmail.com>
>>> Cc: Neil Brown <neilb@suse.com>
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Jeff Layton <jlayton@kernel.org>
>>> ---
>>>  fs/nfsd/nfs4state.c | 3 +--
>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>>> index 6a45fb00c5fc..e87e15df2044 100644
>>> --- a/fs/nfsd/nfs4state.c
>>> +++ b/fs/nfsd/nfs4state.c
>>> @@ -265,6 +265,7 @@ find_or_allocate_block(struct nfs4_lockowner *lo, struct knfsd_fh *fh,
>>>  static void
>>>  free_blocked_lock(struct nfsd4_blocked_lock *nbl)
>>>  {
>>> +	locks_delete_block(&nbl->nbl_lock);
>>>  	locks_release_private(&nbl->nbl_lock);
>>
>> Thanks for tracking this down.
>>
>> An implication of this bug and fix is that we need to be particularly
>> careful to make sure locks_delete_block() is called on all relevant
>> paths.
>> Can we make that easier?  My first thought was to include the call in
>> locks_release_private, but lockd calls the two quite separately and it
>> certainly seems appropriate that locks_delete_block should be called
>> asap, but locks_release_private() can be delayed.
>>
>> Also cifs calls locks_delete_block, but never calls
>> locks_release_private, so it wouldn't help there.
>>
>> Looking at cifs, I think there is a call missing there too.
>> cifs_posix_lock_set() *doesn't* always call locks_delete_block() after
>> waiting.  In particular, if ->can_cache_brlcks becomes true while
>> waiting then I don't think the behaviour is right.... though I'm not
>> sure it is right for other reasons.  It looks like the return value
>> should be 1 in that case, but it'll be zero.
>>
>> But back to my question about making it easier, move the BUG_ON()
>> calls from locks_free_lock() into locks_release_private().
>>
>> ??
>>
>> Thanks,
>> NeilBrown
>>
>>
>>>  	kfree(nbl);
>>>  }
>>> @@ -293,7 +294,6 @@ remove_blocked_locks(struct nfs4_lockowner *lo)
>>>  		nbl = list_first_entry(&reaplist, struct nfsd4_blocked_lock,
>>>  					nbl_lru);
>>>  		list_del_init(&nbl->nbl_lru);
>>> -		locks_delete_block(&nbl->nbl_lock);
>>>  		free_blocked_lock(nbl);
>>>  	}
>>>  }
>>> @@ -4863,7 +4863,6 @@ nfs4_laundromat(struct nfsd_net *nn)
>>>  		nbl = list_first_entry(&reaplist,
>>>  					struct nfsd4_blocked_lock, nbl_lru);
>>>  		list_del_init(&nbl->nbl_lru);
>>> -		locks_delete_block(&nbl->nbl_lock);
>>>  		free_blocked_lock(nbl);
>>>  	}
>>>  out:
>>> -- 
>>> 2.20.1
> 
>