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

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Date:   Tue, 21 Dec 2021 16:08:37 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     Namjae Jeon <linkinjeon@...nel.org>
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

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.

"[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
>>
>>