On Mon, Dec 1, 2014 at 6:05 PM, Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx> wrote:
> On Mon, 1 Dec 2014 17:44:07 -0500
> "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
>
>> On Fri, Nov 21, 2014 at 02:19:28PM -0500, Jeff Layton wrote:
>> > ...also make the manipulation of sp_all_threads list use RCU-friendly
>> > functions.
>> >
>> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
>> > Tested-by: Chris Worley <chris.worley@xxxxxxxxxxxxxxx>
>> > ---
>> > include/linux/sunrpc/svc.h | 2 ++
>> > include/trace/events/sunrpc.h | 3 ++-
>> > net/sunrpc/svc.c | 10 ++++++----
>> > 3 files changed, 10 insertions(+), 5 deletions(-)
>> >
>> > diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
>> > index 5f0ab39bf7c3..7f80a99c59e4 100644
>> > --- a/include/linux/sunrpc/svc.h
>> > +++ b/include/linux/sunrpc/svc.h
>> > @@ -223,6 +223,7 @@ static inline void svc_putu32(struct kvec *iov, __be32 val)
>> > struct svc_rqst {
>> > struct list_head rq_list; /* idle list */
>> > struct list_head rq_all; /* all threads list */
>> > + struct rcu_head rq_rcu_head; /* for RCU deferred kfree */
>> > struct svc_xprt * rq_xprt; /* transport ptr */
>> >
>> > struct sockaddr_storage rq_addr; /* peer address */
>> > @@ -262,6 +263,7 @@ struct svc_rqst {
>> > #define RQ_SPLICE_OK (4) /* turned off in gss privacy
>> > * to prevent encrypting page
>> > * cache pages */
>> > +#define RQ_VICTIM (5) /* about to be shut down */
>> > unsigned long rq_flags; /* flags field */
>> >
>> > void * rq_argp; /* decoded arguments */
>> > diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
>> > index 5848fc235869..08a5fed50f34 100644
>> > --- a/include/trace/events/sunrpc.h
>> > +++ b/include/trace/events/sunrpc.h
>> > @@ -418,7 +418,8 @@ TRACE_EVENT(xs_tcp_data_recv,
>> > { (1UL << RQ_LOCAL), "RQ_LOCAL"}, \
>> > { (1UL << RQ_USEDEFERRAL), "RQ_USEDEFERRAL"}, \
>> > { (1UL << RQ_DROPME), "RQ_DROPME"}, \
>> > - { (1UL << RQ_SPLICE_OK), "RQ_SPLICE_OK"})
>> > + { (1UL << RQ_SPLICE_OK), "RQ_SPLICE_OK"}, \
>> > + { (1UL << RQ_VICTIM), "RQ_VICTIM"})
>> >
>> > TRACE_EVENT(svc_recv,
>> > TP_PROTO(struct svc_rqst *rqst, int status),
>> > diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
>> > index 5d9a443d21f6..4edef32f3b9f 100644
>> > --- a/net/sunrpc/svc.c
>> > +++ b/net/sunrpc/svc.c
>> > @@ -616,7 +616,7 @@ svc_prepare_thread(struct svc_serv *serv, struct svc_pool *pool, int node)
>> > serv->sv_nrthreads++;
>> > spin_lock_bh(&pool->sp_lock);
>> > pool->sp_nrthreads++;
>> > - list_add(&rqstp->rq_all, &pool->sp_all_threads);
>> > + list_add_rcu(&rqstp->rq_all, &pool->sp_all_threads);
>> > spin_unlock_bh(&pool->sp_lock);
>> > rqstp->rq_server = serv;
>> > rqstp->rq_pool = pool;
>> > @@ -684,7 +684,8 @@ found_pool:
>> > * so we don't try to kill it again.
>> > */
>> > rqstp = list_entry(pool->sp_all_threads.next, struct svc_rqst, rq_all);
>> > - list_del_init(&rqstp->rq_all);
>> > + set_bit(RQ_VICTIM, &rqstp->rq_flags);
>> > + list_del_rcu(&rqstp->rq_all);
>> > task = rqstp->rq_task;
>> > }
>> > spin_unlock_bh(&pool->sp_lock);
>> > @@ -782,10 +783,11 @@ svc_exit_thread(struct svc_rqst *rqstp)
>> >
>> > spin_lock_bh(&pool->sp_lock);
>> > pool->sp_nrthreads--;
>> > - list_del(&rqstp->rq_all);
>> > + if (!test_and_set_bit(RQ_VICTIM, &rqstp->rq_flags))
>> > + list_del_rcu(&rqstp->rq_all);
>>
>> Both users of RQ_VICTIM are under the sp_lock, so we don't really need
>> an atomic test_and_set_bit, do we?
>>
>
> No, it doesn't really need to be an atomic test_and_set_bit. We could
> just as easily do:
>
> if (!test_bit(...)) {
> set_bit(...)
> list_del_rcu()
> }
Isn't there a chance that the non-atomic version might end up
clobbering one of the other bits that is not set/cleared under the
sp_lock?
--
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@xxxxxxxxxxxxxxx
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
