linux-kernel - Re: [PATCH] ksmbd: use F_SETLK to force vfs_file

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Message-ID: <CAKYAXd_z9i6VtMsHmR_FQDwBzGHcjHLv=zicAsddjur=_A071g@mail.gmail.com>
Date:   Wed, 22 Dec 2021 11:50:12 +0900
From:   Namjae Jeon <linkinjeon@...nel.org>
To:     Vasily Averin <vvs@...tuozzo.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steve French <sfrench@...ba.org>,
        Hyunchul Lee <hyc.lee@...il.com>, kernel@...nvz.org,
        linux-cifs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ksmbd: use F_SETLK to force vfs_file_lock() to return asynchronously

2021-12-21 22:08 GMT+09:00, Vasily Averin <vvs@...tuozzo.com>:
> On 21.12.2021 15:02, Namjae Jeon wrote:
>> 2021-12-19 18:34 GMT+09:00, Vasily Averin <vvs@...tuozzo.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@...tuozzo.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
>>>
>>>
>
>