#1. Looks like a bug! Lines 629 and 630 should be deleted
#2. See nfs_rpc_free_user_data(). It sets xp_u2 to NULL and drc ref is
decremented there.
#3. Life time of drc should start when it is allocated
in nfs_dupreq_get_drc() using alloc_tcp_drc().
It can live beyond xprt's xp_u2 setting to NULL. It will live until
we decide to free in drc_free_expired() using free_tcp_drc().
Regards, Malahal.
PS: The comment "drc cache maintains a ref count." seems to imply that it
will have a refcount for keeping it in the hash table itself. I may have
kept those two lines because of that but It doesn't make sense as refcnt
will never go to zero this way.
On Thu, Oct 12, 2017 at 3:48 PM, Kinglong Mee <[email protected]> wrote:
> Describes in src/RPCAL/nfs_dupreq.c,
>
> * The life of tcp drc: it gets allocated when we process the first
> * request on the connection. It is put into rbtree (tcp_drc_recycle_t).
> * drc cache maintains a ref count. Every request as well as the xprt
> * holds a ref count. Its ref count should go to zero when the
> * connection's xprt gets freed (all requests should be completed on the
> * xprt by this time). When the ref count goes to zero, it is also put
> * into a recycle queue (tcp_drc_recycle_q). When a reconnection
> * happens, we hope to find the same drc that was used before, and the
> * ref count goes up again. At the same time, the drc will be removed
> * from the recycle queue. Only drc's with ref count zero end up in the
> * recycle queue. If a reconnection doesn't happen in time, the drc gets
> * freed by drc_free_expired() after some period of inactivety.
>
> Some questions about the life time of tcp drc,
> 1. The are two references of drc for xprt in nfs_dupreq_get_drc().
> 629 /* xprt ref */
> 630 drc->refcnt = 1;
> ...
> 638 (void)nfs_dupreq_ref_drc(drc); /* xprt ref
> */
> ...
> 653 req->rq_xprt->xp_u2 = (void *)drc;
>
> I think it's a bug. The first one needs remove. Right?
>
> 2. The is no place to decrease the reference of drc for xprt.
> The xprt argument in nfs_dupreq_put_drc() is unused.
> Should it be used to decrease the ref?
> I think it's the right place to decrease the ref in
> nfs_dupreq_put_drc().
>
> 3. My doubts is that, the life time of drc stored in req->rq_xprt->xp_u2 ?
> Start at #1, end at #2 (req->rq_xprt->xp_u2 = NULL) ?
> If that, the bad case is always lookup drc from tcp_drc_recycle_t.
>
> Otherwise, don't put the reference at #2, when to put it?
> the bad case is the drc ref always be 1 forever, am I right?
>
> thanks,
> Kinglong Mee
>
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