Re: [PATCH 1/7] lockd: introduce safe async lock op

[Benjamin Coddington <bcodding@redhat.com>]

On 10 Sep 2024, at 11:45, Jeff Layton wrote:

> On Tue, 2024-09-10 at 10:18 -0400, Benjamin Coddington wrote:
>> On 23 Aug 2023, at 17:33, Alexander Aring wrote:
>>
>>> This patch reverts mostly commit 40595cdc93ed ("nfs: block notification
>>> on fs with its own ->lock") and introduces an EXPORT_OP_SAFE_ASYNC_LOCK
>>> export flag to signal that the "own ->lock" implementation supports
>>> async lock requests. The only main user is DLM that is used by GFS2 and
>>> OCFS2 filesystem. Those implement their own lock() implementation and
>>> return FILE_LOCK_DEFERRED as return value. Since commit 40595cdc93ed
>>> ("nfs: block notification on fs with its own ->lock") the DLM
>>> implementation were never updated. This patch should prepare for DLM
>>> to set the EXPORT_OP_SAFE_ASYNC_LOCK export flag and update the DLM
>>> plock implementation regarding to it.
>>>
>>> Acked-by: Jeff Layton <jlayton@kernel.org>
>>> Signed-off-by: Alexander Aring <aahringo@redhat.com>
>>> ---
>>>  fs/lockd/svclock.c       |  5 ++---
>>>  fs/nfsd/nfs4state.c      | 13 ++++++++++---
>>>  include/linux/exportfs.h |  8 ++++++++
>>>  3 files changed, 20 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
>>> index c43ccdf28ed9..6e3b230e8317 100644
>>> --- a/fs/lockd/svclock.c
>>> +++ b/fs/lockd/svclock.c
>>> @@ -470,9 +470,7 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
>>>  	    struct nlm_host *host, struct nlm_lock *lock, int wait,
>>>  	    struct nlm_cookie *cookie, int reclaim)
>>>  {
>>> -#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
>>>  	struct inode		*inode = nlmsvc_file_inode(file);
>>> -#endif
>>>  	struct nlm_block	*block = NULL;
>>>  	int			error;
>>>  	int			mode;
>>> @@ -486,7 +484,8 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
>>>  				(long long)lock->fl.fl_end,
>>>  				wait);
>>>
>>> -	if (nlmsvc_file_file(file)->f_op->lock) {
>>> +	if (!export_op_support_safe_async_lock(inode->i_sb->s_export_op,
>>> +					       nlmsvc_file_file(file)->f_op)) {
>>
>> ... but don't most filesystem use VFS' posix_lock_file(), which does the
>> right thing?  I think this patch has broken async lock callbacks for NLM for
>> all the other filesystems that just use posix_lock_file().
>>
>> Maybe I'm missing something, but why was that necessary?
>>
>
> Good catch. Yeah, I think that probably should have been an &&
> condition. IOW:
>
> 	if (nlmsvc_file_file(file)->f_op->lock &&
>             !export_op_support_safe_async_lock(inode->i_sb->s_export_op,
>

Ah Jeff, thanks for confirming - there's been a bunch of changes in there that
made me uncertain.  I can send a patch for this, I'd like to rename
export_op_support_safe_async_lock to something like fs_can_defer_lock
(suggestions) and put the test in there.

Ben