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

[NeilBrown <neilb@suse.com>]

[-- Attachment #1: Type: text/plain, Size: 3105 bytes --]

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

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 832 bytes --]