linux-kernel - Re: [PATCH v3 2/3] nfs4: handle async processing of F_SETLK with FL

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Message-ID: <b332a1dd-f96d-2d83-80ca-67058eeaa1af@virtuozzo.com>
Date:   Sun, 16 Jan 2022 15:25:43 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     "J. Bruce Fields" <bfields@...ldses.org>
Cc:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>, kernel@...nvz.org,
        linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chuck Lever <chuck.lever@...cle.com>
Subject: Re: [PATCH v3 2/3] nfs4: handle async processing of F_SETLK with
 FL_SLEEP

On 03.01.2022 22:40, J. Bruce Fields wrote:
> On Wed, Dec 29, 2021 at 11:24:43AM +0300, Vasily Averin wrote:
>> nfsd and lockd use F_SETLK cmd with the FL_SLEEP flag set to request
>> asynchronous processing of blocking locks.
>>
>> Currently nfs4 use locks_lock_inode_wait() function which is blocked
>> for such requests. To handle them correctly FL_SLEEP flag should be
>> temporarily reset before executing the locks_lock_inode_wait() function.
>>
>> Additionally block flag is forced to set, to translate blocking lock to
>> remote nfs server, expecting it supports async processing of the blocking
>> locks too.
> 
> Seems like an improvement, but is there some way to make this more
> straightforward by just calling a function that doesn't sleep in the
> first place?  (posix_lock_inode(), maybe?)

There are few problems:
1) posix_lock_inode() is static in fs/locks.c
2) exported posix_lock_file() used posix_lock_inode() inside requires file pointer,
and I do not understand how to get it.
3) _nfs4_do_setlk() is called from do_setlk and handles flocks too, 
therefore any posix-only calls requires additional checks or branches.

On the other hand all that is required to handle F_SETLK with FL_SLEEP correctly :
to avoid blocking on exiting lock. We can reach this goal here by drop of FL_SLEEP flag
before locks_lock_inode_wait() execution.

Thank you,
	Vasily Averin

PS I'm worry for a long delay with answer,
in Russia we have long holidays after New Year,
then I dealt with urgent tasks accumulated over the holidays
then I forgot the context of this patch and 
I was need to spend some time to re-member the details.

>> https://bugzilla.kernel.org/show_bug.cgi?id=215383
>> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
>> ---
>>  fs/nfs/nfs4proc.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
>> index ee3bc79f6ca3..9b1380c4223c 100644
>> --- a/fs/nfs/nfs4proc.c
>> +++ b/fs/nfs/nfs4proc.c
>> @@ -7094,7 +7094,7 @@ static int _nfs4_do_setlk(struct nfs4_state *state, int cmd, struct file_lock *f
>>  			recovery_type == NFS_LOCK_NEW ? GFP_KERNEL : GFP_NOFS);
>>  	if (data == NULL)
>>  		return -ENOMEM;
>> -	if (IS_SETLKW(cmd))
>> +	if (IS_SETLKW(cmd) || (fl->fl_flags & FL_SLEEP))
>>  		data->arg.block = 1;
>>  	nfs4_init_sequence(&data->arg.seq_args, &data->res.seq_res, 1,
>>  				recovery_type > NFS_LOCK_NEW);
>> @@ -7200,6 +7200,9 @@ static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock
>>  	int status;
>>  
>>  	request->fl_flags |= FL_ACCESS;
>> +	if (((fl_flags & FL_SLEEP_POSIX) == FL_SLEEP_POSIX) && IS_SETLK(cmd))
>> +		request->fl_flags &= ~FL_SLEEP;
>> +
>>  	status = locks_lock_inode_wait(state->inode, request);
>>  	if (status < 0)
>>  		goto out;
>> -- 
>> 2.25.1