Re: [PATCH v2 1/2] nfsd: wake waiters blocked on file_lock before deleting it

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Apr 24, 2019 at 11:29:59AM -0400, Steve Dickson wrote:
> 
> 
> On 4/24/19 9:58 AM, J. Bruce Fields wrote:
> > Steve, see Neil's comment, is there a cifs bug here?
> Looking into it... 

I was thinking Steve French, though I'm sure he wouldn't mind if you
fixed cifs bugs.  Too many Steves!

--b.

> 
> steved.
> > 
> > --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
> > 
> >