From: "J. Bruce Fields" <bfields@fieldses.org>
To: Vasily Averin <vvs@virtuozzo.com>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>,
Anna Schumaker <anna.schumaker@netapp.com>,
kernel@openvz.org, linux-nfs@vger.kernel.org,
linux-kernel@vger.kernel.org,
Chuck Lever <chuck.lever@oracle.com>
Subject: Re: [PATCH v3 2/3] nfs4: handle async processing of F_SETLK with FL_SLEEP
Date: Tue, 18 Jan 2022 17:35:05 -0500 [thread overview]
Message-ID: <20220118223505.GE16108@fieldses.org> (raw)
In-Reply-To: <7666958f-6215-a8eb-3412-b613158406db@virtuozzo.com>
On Sun, Jan 16, 2022 at 03:44:21PM +0300, Vasily Averin wrote:
> On 03.01.2022 22:53, 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.
> >
> > But this on its own isn't enough for the client to support asynchronous
> > blocking locks, right? Don't we also need the logic that calls knfsd's
> > lm_notify when it gets a CB_NOTIFY_LOCK from the server?
>
> No, I think this should be enough.
> We are here a nfs client,
> we can get F_SETLK with FL_SLEEP from nfsd only (i.e. in re-export case)
> we need to avoid blocking if lock is already taken,
> so we need to call locks_lock_inode_wait without FL_SLEEP,
> then we submit _sleeping_ request to NFS server (i.e. set )data->arg.block = 1)
> and waiting for reply from server.
>
> Here we rely that server will NOT block on such request too, so our reply wel not be blocked too.
Just on that one point: if there's a lock conflict, an NFSv4 server will
return NFS4ERR_DENIED immediately and leave it to the client to poll.
Or if you're using NFS version >= 4.1, the server has the option of
calling back to the client with a CB_NOTIFY_LOCK to let the client know
when the lock might be available. (See
https://datatracker.ietf.org/doc/html/rfc8881#section-20.11 for
details.) But if a server that blocked and didn't reply to the original
LOCK request until the lock became available, that would be a bug.
(Apologies for responding just to that one point, I'm also trying to get
caught back up again here....).
--b.
> Under "block" I mean that handler can sleep or process request for a very long time
> but it will NOT BE BLOCKED if lock is taken already, it WILL NOT WAIT when lock will be released,
> it just return some error in this case.
>
> I think it is correct.
> Do you think I am wrong or maybe I missed something?
>
> Thank you,
> Vasily Averin
>
> However I noticed now that past is incorrect,
> temporally dropped FL_SLEEP should be restored back in _nfs4_proc_setlk before _nfs4_do_setlk() call.
> I'll fix it in next version of this patch-set.
>
> >> https://bugzilla.kernel.org/show_bug.cgi?id=215383
> >> Signed-off-by: Vasily Averin <vvs@virtuozzo.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
next prev parent reply other threads:[~2022-01-18 22:35 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-27 10:45 [PATCH] nfs4: handle async processing of F_SETLK with FL_SLEEP Vasily Averin
2021-12-27 15:51 ` [PATCH v2] " Vasily Averin
2021-12-28 1:04 ` Vasily Averin
2021-12-29 8:24 ` [PATCH v3 1/3] nfs: local_lock: " Vasily Averin
2021-12-29 8:24 ` [PATCH v3 2/3] nfs4: " Vasily Averin
2022-01-03 19:40 ` J. Bruce Fields
2022-01-16 12:25 ` Vasily Averin
2022-01-03 19:53 ` J. Bruce Fields
2022-01-16 12:44 ` Vasily Averin
2022-01-16 18:28 ` Vasily Averin
2022-01-18 22:35 ` J. Bruce Fields [this message]
2021-12-29 8:24 ` [PATCH v3 3/3] nfs v2/3: nlmclnt_lock: " Vasily Averin
2021-12-27 17:58 ` [PATCH] nfs4: " kernel test robot
2022-01-06 10:37 ` Dan Carpenter
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