[ Upstream commit 46b1c18f9deb326a7e18348e668e4c7ab7c7458b ]

In the series fc8b81a5981f ("Merge branch 'lockless-qdisc-series'")
John made the assumption that the data path had no need to read
the qdisc qlen (number of packets in the qdisc).

It is true when pfifo_fast is used as the root qdisc, or as direct MQ/MQPRIO
children.

But pfifo_fast can be used as leaf in class full qdiscs, and existing
logic needs to access the child qlen in an efficient way.

HTB breaks badly, since it uses cl->leaf.q->q.qlen in :
  htb_activate() -> WARN_ON()
  htb_dequeue_tree() to decide if a class can be htb_deactivated
  when it has no more packets.

HFSC, DRR, CBQ, QFQ have similar issues, and some calls to
qdisc_tree_reduce_backlog() also read q.qlen directly.

Using qdisc_qlen_sum() (which iterates over all possible cpus)
in the data path is a non starter.

It seems we have to put back qlen in a central location,
at least for stable kernels.

For all qdisc but pfifo_fast, qlen is guarded by the qdisc lock,
so the existing q.qlen{++|--} are correct.

For 'lockless' qdisc (pfifo_fast so far), we need to use atomic_{inc|dec}()
because the spinlock might be not held (for example from
pfifo_fast_enqueue() and pfifo_fast_dequeue())

This patch adds atomic_qlen (in the same location than qlen)
and renames the following helpers, since we want to express
they can be used without qdisc lock, and that qlen is no longer percpu.

- qdisc_qstats_cpu_qlen_dec -> qdisc_qstats_atomic_qlen_dec()
- qdisc_qstats_cpu_qlen_inc -> qdisc_qstats_atomic_qlen_inc()

Later (net-next) we might revert this patch by tracking all these
qlen uses and replace them by a more efficient method (not having
to access a precise qlen, but an empty/non_empty status that might
be less expensive to maintain/track).

Another possibility is to have a legacy pfifo_fast version that would
be used when used a a child qdisc, since the parent qdisc needs
a spinlock anyway. But then, future lockless qdiscs would also
have the same problem.

Fixes: 7e66016f2c65 ("net: sched: helpers to sum qlen and qlen for per cpu logic")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The gen_stats facility will add a header for the toplevel nlattr of type
TCA_STATS2 that contains all stats added by qdisc callbacks. A reference
to this header is stored in the gnet_dump struct, and when all the
per-qdisc callbacks have finished adding their stats, the length of the
containing header will be adjusted to the right value.

However, on architectures that need padding (i.e., that don't set
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS), the padding nlattr is added
before the stats, which means that the stored pointer will point to the
padding, and so when the header is fixed up, the result is just a very
big padding nlattr. Because most qdiscs also supply the legacy TCA_STATS
struct, this problem has been mostly invisible, but we exposed it with
the netlink attribute-based statistics in CAKE.

Fix the issue by fixing up the stored pointer if it points to a padding
nlattr.

Tested-by: Pete Heist <pete@heistp.net>
Tested-by: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>

The sch_mq qdisc creates a sub-qdisc per tx queue which are then
called independently for enqueue and dequeue operations. However
statistics are aggregated and pushed up to the "master" qdisc.

This patch adds support for any of the sub-qdiscs to be per cpu
statistic qdiscs. To handle this case add a check when calculating
stats and aggregate the per cpu stats if needed.

Also exports __gnet_stats_copy_queue() to use as a helper function.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1) Old code was hard to maintain, due to complex lock chains.
   (We probably will be able to remove some kfree_rcu() in callers)

2) Using a single timer to update all estimators does not scale.

3) Code was buggy on 32bit kernel (WRITE_ONCE() on 64bit quantity
   is not supposed to work well)

In this rewrite :

- I removed the RB tree that had to be scanned in
  gen_estimator_active(). qdisc dumps should be much faster.

- Each estimator has its own timer.

- Estimations are maintained in net_rate_estimator structure,
  instead of dirtying the qdisc. Minor, but part of the simplification.

- Reading the estimator uses RCU and a seqcount to provide proper
  support for 32bit kernels.

- We reduce memory need when estimators are not used, since
  we store a pointer, instead of the bytes/packets counters.

- xt_rateest_mt() no longer has to grab a spinlock.
  (In the future, xt_rateest_tg() could be switched to per cpu counters)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Conflicts:
	net/sched/act_police.c
	net/sched/sch_drr.c
	net/sched/sch_hfsc.c
	net/sched/sch_prio.c
	net/sched/sch_red.c
	net/sched/sch_tbf.c

In net-next the drop methods of the packet schedulers got removed, so
the bug fixes to them in 'net' are irrelevant.

A packet action unload crash fix conflicts with the addition of the
new firstuse timestamp.

Signed-off-by: David S. Miller <davem@davemloft.net>

"make htmldocs" complains otherwise:

.//net/core/gen_stats.c:168: warning: No description found for parameter 'running'
.//include/linux/netdevice.h:1867: warning: No description found for parameter 'qdisc_running_key'

Fixes: f9eb8aea2a1e ("net_sched: transform qdisc running bit into a seqcount")
Fixes: edb09eb17ed8 ("net: sched: do not acquire qdisc spinlock in qdisc/class stats dump")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

"make htmldocs" complains otherwise:

.//net/core/gen_stats.c:65: warning: No description found for parameter 'padattr'
.//net/core/gen_stats.c:101: warning: No description found for parameter 'padattr'

Fixes: 9854518ea04d ("sched: align nlattr properly when needed")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Large tc dumps (tc -s {qdisc|class} sh dev ethX) done by Google BwE host
agent [1] are problematic at scale :

For each qdisc/class found in the dump, we currently lock the root qdisc
spinlock in order to get stats. Sampling stats every 5 seconds from
thousands of HTB classes is a challenge when the root qdisc spinlock is
under high pressure. Not only the dumps take time, they also slow
down the fast path (queue/dequeue packets) by 10 % to 20 % in some cases.

An audit of existing qdiscs showed that sch_fq_codel is the only qdisc
that might need the qdisc lock in fq_codel_dump_stats() and
fq_codel_dump_class_stats()

In v2 of this patch, I now use the Qdisc running seqcount to provide
consistent reads of packets/bytes counters, regardless of 32/64 bit arches.

I also changed rate estimators to use the same infrastructure
so that they no longer need to lock root qdisc lock.

[1]
http://static.googleusercontent.com/media/research.google.com/en//pubs/archive/43838.pdf

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Kevin Athey <kda@google.com>
Cc: Xiaotian Pei <xiaotian@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Function gnet_stats_copy_basic is missing the description of the cpu
argument in the documentation. Adding it.

Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>