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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Ido Schimmel <idosch@idosch.org>, Neil Brown <neilb@suse.de>
CC:     Bruce Fields <bfields@fieldses.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH 13/20] lockd: move lockd_start_svc() call into
 lockd_create_svc()
Thread-Topic: [PATCH 13/20] lockd: move lockd_start_svc() call into
 lockd_create_svc()
Thread-Index: AQHX5N0WWgW13Lz0b0Kb4xgS36Hhoq97CRkAgABfhACAAMqoAIAAWryA
Date:   Sat, 3 Jun 2023 14:58:44 +0000
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> On Jun 3, 2023, at 5:33 AM, Ido Schimmel <idosch@idosch.org> wrote:
>=20
> On Sat, Jun 03, 2023 at 07:28:28AM +1000, NeilBrown wrote:
>> From: NeilBrown <neilb@suse.de>
>> Date: Sat, 3 Jun 2023 07:14:14 +1000
>> Subject: [PATCH] lockd: drop inappropriate svc_get() from locked_get()
>>=20
>> The below-mentioned patch was intended to simplify refcounting on the
>> svc_serv used by locked.  The goal was to only ever have a single
>> reference from the single thread.  To that end we dropped a call to
>> lockd_start_svc() (except when creating thread) which would take a
>> reference, and dropped the svc_put(serv) that would drop that reference.
>>=20
>> Unfortunately we didn't also remove the svc_get() from
>> lockd_create_svc() in the case where the svc_serv already existed.
>> So after the patch:
>> - on the first call the svc_serv was allocated and the one reference
>>   was given to the thread, so there are no extra references
>> - on subsequent calls svc_get() was called so there is now an extra
>>   reference.
>> This is clearly not consistent.
>>=20
>> The inconsistency is also clear in the current code in lockd_get()
>> takes *two* references, one on nlmsvc_serv and one by incrementing
>> nlmsvc_users.   This clearly does not match lockd_put().
>>=20
>> So: drop that svc_get() from lockd_get() (which used to be in
>> lockd_create_svc().
>>=20
>> Reported-by: Ido Schimmel <idosch@idosch.org>
>> Fixes: b73a2972041b ("lockd: move lockd_start_svc() call into lockd_crea=
te_svc()")
>> Signed-off-by: NeilBrown <neilb@suse.de>
>=20
> Thanks for the quick fix. I no longer see the memory leak with this
> patch.
>=20
> Tested-by: Ido Schimmel <idosch@nvidia.com>

Since we are getting close to the merge window, I've applied this
fix to nfsd-next.


--
Chuck Lever