Re: [PATCH v3 2/3] nfs4: handle async processing of F_SETLK with FL_SLEEP

From: Vasily Averin
Date: Sun Jan 16 2022 - 07:25:54 EST


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@xxxxxxxxxxxxx>
>> ---
>> 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