Re: [PATCH] ksmbd: use F_SETLK to force vfs_file_lock() to return asynchronously

From: Namjae Jeon <linkinjeon@kernel.org>
To: Vasily Averin <vvs@virtuozzo.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
	Steve French <sfrench@samba.org>,
	Hyunchul Lee <hyc.lee@gmail.com>,
	kernel@openvz.org, linux-cifs@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ksmbd: use F_SETLK to force vfs_file_lock() to return asynchronously
Date: Wed, 22 Dec 2021 11:50:12 +0900	[thread overview]
Message-ID: <CAKYAXd_z9i6VtMsHmR_FQDwBzGHcjHLv=zicAsddjur=_A071g@mail.gmail.com> (raw)
In-Reply-To: <bf92bd1f-d03b-1fb6-ff62-53cca4b441e8@virtuozzo.com>

2021-12-21 22:08 GMT+09:00, Vasily Averin <vvs@virtuozzo.com>:
> On 21.12.2021 15:02, Namjae Jeon wrote:
>> 2021-12-19 18:34 GMT+09:00, Vasily Averin <vvs@virtuozzo.com>:
>>> To avoid possible deadlock ksmbd should process locks asynchronously.
>>> Callers expecting vfs_file_locks() to return asynchronously should only
>>> use F_SETLK, not F_SETLKW.
>> Should I check this patch instead of
>> [PATCH] ksmbd: force "fail immediately" flag on fs with its own ->lock ?
>
> no, these patches are independent and both ones are required.
> current patch fixes incorrect kernel thread behaviour:
> kernel threads should not use F_SETLKW for locking requests.
How does this patch work? posix_lock_file in vfs_lock_file() does not use cmd.
And your patch still leaves FL_SLEEP.

>
> "[PATCH] ksmbd: force "fail immediately" flag on fs with its own ->lock"
> tries to workaround the incorrect behaviour of some exported filesystems.
>
> Currently this way is used in nfsd and lockd, however it is not fully
> correct,
> and I still search some better solution, so perhaps
> '[PATCH] ksmbd: force "fail immediately" flag on fs with its own ->lock'
> will be dropped later.
>
> Thank you,
> 	Vasily Averin
>
>>> Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
>>> ---
>>>  fs/ksmbd/smb2pdu.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
>>> index 0c020deb76bb..34f333549767 100644
>>> --- a/fs/ksmbd/smb2pdu.c
>>> +++ b/fs/ksmbd/smb2pdu.c
>>> @@ -6646,13 +6646,13 @@ static int smb2_set_flock_flags(struct file_lock
>>> *flock, int flags)
>>>  	switch (flags) {
>>>  	case SMB2_LOCKFLAG_SHARED:
>>>  		ksmbd_debug(SMB, "received shared request\n");
>>> -		cmd = F_SETLKW;
>>> +		cmd = F_SETLK;
>>>  		flock->fl_type = F_RDLCK;
>>>  		flock->fl_flags |= FL_SLEEP;
>>>  		break;
>>>  	case SMB2_LOCKFLAG_EXCLUSIVE:
>>>  		ksmbd_debug(SMB, "received exclusive request\n");
>>> -		cmd = F_SETLKW;
>>> +		cmd = F_SETLK;
>>>  		flock->fl_type = F_WRLCK;
>>>  		flock->fl_flags |= FL_SLEEP;
>>>  		break;
>>> --
>>> 2.25.1
>>>
>>>
>
>