linux-kernel - Re: [NFS] 2.6.17.8 - do_vfs_lock: VFS is out of sync with lock manager!

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Message-ID: <9a8748490611210443w7711b962u3fb35aef14746582@mail.gmail.com>
Date:	Tue, 21 Nov 2006 13:43:43 +0100
From:	"Jesper Juhl" <jesper.juhl@...il.com>
To:	"Trond Myklebust" <trond.myklebust@....uio.no>
Cc:	"Neil Brown" <neilb@...e.de>, nfs@...ts.sourceforge.net,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [NFS] 2.6.17.8 - do_vfs_lock: VFS is out of sync with lock manager!

On 21/08/06, Trond Myklebust <trond.myklebust@....uio.no> wrote:
> On Mon, 2006-08-21 at 13:34 +1000, Neil Brown wrote:
> > Looking in fs/nfs/file.c (at 2.6.18-rc4-mm1 if it matters, but 2.6.17
> > is much the same)
> >
> >  - do_vfs_lock is only called when the filesystem was mounted with
> >     -o nolock  EXCEPT
> >  - If a lock request to the server in interrupted (when mounted with
> >      -o intr) then do_vfs_lock is called to try to get the lock
> >     locally.  Normally equivalent code will be called inside
> >     fs/lockd/clntproc.c when the server replies that the lock has been
> >     gained.  In the case of an interrupt though this doesn't happen
> >     but the lock may still have happened on the server.  So we record
> >     locally that the lock was gained, to ensure that it gets unlocked
> >     when the process exits.
> >
> > As you don't have '-o nolocks' you must be hitting the second case.
> > The lock call to the server returns -EINTR or -ERESTARTSYS and
> > do_vfs_lock is called just-in-case.
> > As this is a just-in-case call, it is quite possible that the lock is
> > held by some other process, so getting an error is entirely possible.
> > So printing the message in this case seems wrong.
> >
> > On the other hand, printing the message in any other case seems wrong
> > too, as server locking is not being used, so there is nothing to get
> > out of sync with.
> >
> > As a further complication, I don't think that in the just-in-case
> > situation that it should risk waiting for the lock.
> > Now maybe we can be sure there is a pending signal which will break
> > out of any wait (though I'm worried about -ERESTARTSYS - that doesn't
> > imply a signal does it?), but I would feel more comfortable if
> > FL_SLEEP were turned off in that path.
> >
> > So: Trond:  Any obvious errors in the above?
> > Is the following patch ok?
>
> Could we instead replace it with a dprintk() that returns the value of
> "res"? That will keep it useful for debugging purposes.
>

How about the below?
(compile tested only)

Neil: I left your Signed-off-by line since I just modified your patch slightly.

Since Gmail will probably mangle the inline patch, it is attached as well.


Signed-off-by: Neil Brown <neilb@...e.de>
Signed-off-by: Jesper Juhl <jesper.juhl@...il.com>
--

 fs/nfs/file.c |   11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index cc93865..22572af 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -428,8 +428,8 @@ static int do_vfs_lock(struct file *file
                        BUG();
        }
        if (res < 0)
-               printk(KERN_WARNING "%s: VFS is out of sync with lock
manager!\n",
-                               __FUNCTION__);
+               dprintk("%s: VFS is out of sync with lock manager (res
= %d)!\n",
+                               __FUNCTION__, res);
        return res;
 }

@@ -479,10 +479,13 @@ static int do_setlk(struct file *filp, i
                 * we clean up any state on the server. We therefore
                 * record the lock call as having succeeded in order to
                 * ensure that locks_remove_posix() cleans it out when
-                * the process exits.
+                * the process exits. Make sure not to sleep if
+                * someone else holds the lock.
                 */
-               if (status == -EINTR || status == -ERESTARTSYS)
+               if (status == -EINTR || status == -ERESTARTSYS) {
+                       fl->fl_flags &= ~FL_SLEEP;
                        do_vfs_lock(filp, fl);
+               }
        } else
                status = do_vfs_lock(filp, fl);
        unlock_kernel();



-- 
Jesper Juhl <jesper.juhl@...il.com>
Don't top-post  http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please      http://www.expita.com/nomime.html

View attachment "VFS_is_out_of_sync_with_lock_manager.diff" of type "text/x-patch" (1176 bytes)