linux-kernel - [PATCH v3 3/3] nfs v2/3: nlmclnt_lock: handle async processing of F_SETLK with FL

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Message-ID: <dc99ce3c-d73f-b21b-b92f-d0b1025c4567@virtuozzo.com>
Date:   Wed, 29 Dec 2021 11:24:53 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        "J. Bruce Fields" <bfields@...ldses.org>
Cc:     kernel@...nvz.org, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, Chuck Lever <chuck.lever@...cle.com>
Subject: [PATCH v3 3/3] nfs v2/3: nlmclnt_lock: handle async processing of
 F_SETLK with FL_SLEEP

nfsd and lockd use F_SETLK cmd with the FL_SLEEP flag set to request
asynchronous processing of blocking locks.

Currently nfs v2/3 handles such requests by using nlmclnt_lock() ->
do_vfs_lock() -> locks_lock_inode_wait() function which is blocked
if request have FL_SLEEP flag set.

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.

https://bugzilla.kernel.org/show_bug.cgi?id=215383
Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
---
 fs/lockd/clntproc.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/lockd/clntproc.c b/fs/lockd/clntproc.c
index 99fffc9cb958..5941aa7c9cc9 100644
--- a/fs/lockd/clntproc.c
+++ b/fs/lockd/clntproc.c
@@ -519,11 +519,18 @@ nlmclnt_lock(struct nlm_rqst *req, struct file_lock *fl)
 	unsigned char fl_flags = fl->fl_flags;
 	unsigned char fl_type;
 	int status = -ENOLCK;
+	bool async = false;
 
 	if (nsm_monitor(host) < 0)
 		goto out;
 	req->a_args.state = nsm_local_state;
 
+	async = !req->a_args.block &&
+		((fl_flags & FL_SLEEP_POSIX) == FL_SLEEP_POSIX);
+	if (async) {
+		fl->fl_flags &= ~FL_SLEEP;
+		req->a_args.block = 1;
+	}
 	fl->fl_flags |= FL_ACCESS;
 	status = do_vfs_lock(fl);
 	fl->fl_flags = fl_flags;
@@ -573,8 +580,11 @@ nlmclnt_lock(struct nlm_rqst *req, struct file_lock *fl)
 			up_read(&host->h_rwsem);
 			goto again;
 		}
-		/* Ensure the resulting lock will get added to granted list */
-		fl->fl_flags |= FL_SLEEP;
+		if (async)
+			fl->fl_flags &= ~FL_SLEEP;
+		else
+			/* Ensure the resulting lock will get added to granted list */
+			fl->fl_flags |= FL_SLEEP;
 		if (do_vfs_lock(fl) < 0)
 			printk(KERN_WARNING "%s: VFS is out of sync with lock manager!\n", __func__);
 		up_read(&host->h_rwsem);
-- 
2.25.1