Re: [PATCH 1/4] virtiofsd: Release file locks using F_UNLCK

[Vivek Goyal]

On Fri, Nov 22, 2019 at 10:07:13AM +0000, Stefan Hajnoczi wrote:
> On Fri, Nov 15, 2019 at 03:55:40PM -0500, Vivek Goyal wrote:
> > diff --git a/contrib/virtiofsd/passthrough_ll.c 
> > b/contrib/virtiofsd/passthrough_ll.c
> > index bc214df0c7..028e7da273 100644
> > --- a/contrib/virtiofsd/passthrough_ll.c
> > +++ b/contrib/virtiofsd/passthrough_ll.c
> > @@ -936,6 +936,14 @@ static void put_shared(struct lo_data *lo, struct 
> > lo_inode *inode)
> >     }
> >  }
> >  
> > +static void release_plock(gpointer data)
> 
> The name posix_locks_value_destroy() would be clearer because it matches
> g_hash_table_new_full() terminology and the function cannot be confused
> with a lock acquire/release operation.

Ok, will use this name.

> 
> This patch conflicts with the cleanups that are currently being made to
> virtiofsd:
> https://github.com/stefanha/qemu/commit/1e493175feca58a81a2d0cbdac93b92e5425d850#diff-ca2dea995d1e6cdb95c8a47c7cca51ceR773

Yes it will. I see you are removing element from hash table on lo_flush().
This works fine today but with waiting locks, we drop the
inode->plock_mutex lock and then wait for the lock and expect
"lo_inode_plock" to not go away.

So I don't think you can remove the element from hash table upon
lo_flush(). May be we can refcount lo_inode_plock structure and first
release all the locks using setlk(UNLCK) and then drop the reference. If
this is last refernce, it will be freed.

And waiting lock code, will obtain a refernce under inode->posix_locks
and then wait for lock outside the lock.

IOW, I will say don't do this optimization of lookup + remove because
it will not work with blocking locks.

Thanks
Vivek