Date:   Wed, 24 Apr 2019 09:58:54 -0400
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     NeilBrown <neilb@suse.com>
Cc:     Jeff Layton <jlayton@kernel.org>, slawek1211@gmail.com,
        linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org,
        Steve French <smfrench@gmail.com>
Subject: Re: [PATCH v2 1/2] nfsd: wake waiters blocked on file_lock before
 deleting it
Message-ID: <20190424135854.GB20542@fieldses.org>
References: <20190422163424.19402-1-jlayton@kernel.org>
 <20190422163424.19402-2-jlayton@kernel.org>
 <87wojl61s5.fsf@notabene.neil.brown.name>
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Steve, see Neil's comment, is there a cifs bug here?

--b.

On Tue, Apr 23, 2019 at 09:47:06AM +1000, NeilBrown wrote:
> On Mon, Apr 22 2019, Jeff Layton wrote:
> 
> > After a blocked nfsd file_lock request is deleted, knfsd will send a
> > callback to the client and then free the request. Commit 16306a61d3b7
> > ("fs/locks: always delete_block after waiting.") changed it such that
> > locks_delete_block is always called on a request after it is awoken,
> > but that patch missed fixing up blocked nfsd request handling.
> >
> > Call locks_delete_block on the block to wake up any locks still blocked
> > on the nfsd lock request before freeing it. Some of its callers already
> > do this however, so just remove those calls.
> >
> > URL: https://bugzilla.kernel.org/show_bug.cgi?id=203363
> > Fixes: 16306a61d3b7 ("fs/locks: always delete_block after waiting.")
> > Reported-by: Slawomir Pryczek <slawek1211@gmail.com>
> > Cc: Neil Brown <neilb@suse.com>
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >  fs/nfsd/nfs4state.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > index 6a45fb00c5fc..e87e15df2044 100644
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -265,6 +265,7 @@ find_or_allocate_block(struct nfs4_lockowner *lo, struct knfsd_fh *fh,
> >  static void
> >  free_blocked_lock(struct nfsd4_blocked_lock *nbl)
> >  {
> > +	locks_delete_block(&nbl->nbl_lock);
> >  	locks_release_private(&nbl->nbl_lock);
> 
> Thanks for tracking this down.
> 
> An implication of this bug and fix is that we need to be particularly
> careful to make sure locks_delete_block() is called on all relevant
> paths.
> Can we make that easier?  My first thought was to include the call in
> locks_release_private, but lockd calls the two quite separately and it
> certainly seems appropriate that locks_delete_block should be called
> asap, but locks_release_private() can be delayed.
> 
> Also cifs calls locks_delete_block, but never calls
> locks_release_private, so it wouldn't help there.
> 
> Looking at cifs, I think there is a call missing there too.
> cifs_posix_lock_set() *doesn't* always call locks_delete_block() after
> waiting.  In particular, if ->can_cache_brlcks becomes true while
> waiting then I don't think the behaviour is right.... though I'm not
> sure it is right for other reasons.  It looks like the return value
> should be 1 in that case, but it'll be zero.
> 
> But back to my question about making it easier, move the BUG_ON()
> calls from locks_free_lock() into locks_release_private().
> 
> ??
> 
> Thanks,
> NeilBrown
> 
> 
> >  	kfree(nbl);
> >  }
> > @@ -293,7 +294,6 @@ remove_blocked_locks(struct nfs4_lockowner *lo)
> >  		nbl = list_first_entry(&reaplist, struct nfsd4_blocked_lock,
> >  					nbl_lru);
> >  		list_del_init(&nbl->nbl_lru);
> > -		locks_delete_block(&nbl->nbl_lock);
> >  		free_blocked_lock(nbl);
> >  	}
> >  }
> > @@ -4863,7 +4863,6 @@ nfs4_laundromat(struct nfsd_net *nn)
> >  		nbl = list_first_entry(&reaplist,
> >  					struct nfsd4_blocked_lock, nbl_lru);
> >  		list_del_init(&nbl->nbl_lru);
> > -		locks_delete_block(&nbl->nbl_lock);
> >  		free_blocked_lock(nbl);
> >  	}
> >  out:
> > -- 
> > 2.20.1