linux.git/include/net/sch_generic.h, branch v6.1

net/sched: query offload capabilities through ndo_setup_tc()

2022-09-30T01:52:01+00:00

When adding optional new features to Qdisc offloads, existing drivers
must reject the new configuration until they are coded up to act on it.

Since modifying all drivers in lockstep with the changes in the Qdisc
can create problems of its own, it would be nice if there existed an
automatic opt-in mechanism for offloading optional features.

Jakub proposes that we multiplex one more kind of call through
ndo_setup_tc(): one where the driver populates a Qdisc-specific
capability structure.

First user will be taprio in further changes. Here we are introducing
the definitions for the base functionality.

Link: https://patchwork.kernel.org/project/netdevbpf/patch/20220923163310.3192733-3-vladimir.oltean@nxp.com/
Suggested-by: Jakub Kicinski 
Co-developed-by: Jakub Kicinski 
Signed-off-by: Vladimir Oltean 
Signed-off-by: Jakub Kicinski

net: sched: remove unused tcf_result extension

2022-09-22T01:32:33+00:00

Added by:
commit e5cf1baf92cb ("act_mirred: use TC_ACT_REINSERT when possible")
but no longer useful.

Signed-off-by: Jamal Hadi Salim 
Link: https://lore.kernel.org/r/20220919130627.3551233-1-jhs@mojatatu.com
Signed-off-by: Jakub Kicinski

net: sched: remove unnecessary init of qdisc skb head

2022-08-26T11:03:04+00:00

The memory allocated by using kzallloc_node and kcalloc has been cleared.
Therefore, the structure members of the new qdisc are 0. So there's no
need to explicitly assign a value of 0.

Signed-off-by: Zhengchao Shao 
Signed-off-by: David S. Miller

net: sched: delete duplicate cleanup of backlog and qlen

2022-08-25T13:10:17+00:00

qdisc_reset() is clearing qdisc->q.qlen and qdisc->qstats.backlog
_after_ calling qdisc->ops->reset. There is no need to clear them
again in the specific reset function.

Signed-off-by: Zhengchao Shao 
Link: https://lore.kernel.org/r/20220824005231.345727-1-shaozhengchao@huawei.com
Signed-off-by: Paolo Abeni

net/sched: remove qdisc_root_lock() helper

2022-07-20T00:14:55+00:00

the last caller has been removed with commit 96f5e66e8a79 ("mac80211: fix
aggregation for hardware with ampdu queues"), so it's safe to remove this
function.

Signed-off-by: Davide Caratti 
Link: https://lore.kernel.org/r/703d549e3088367651d92a059743f1be848d74b7.1658133689.git.dcaratti@redhat.com
Signed-off-by: Jakub Kicinski

net: sched: add barrier to fix packet stuck problem for lockless qdisc

2022-06-01T03:39:28+00:00

In qdisc_run_end(), the spin_unlock() only has store-release semantic,
which guarantees all earlier memory access are visible before it. But
the subsequent test_bit() has no barrier semantics so may be reordered
ahead of the spin_unlock(). The store-load reordering may cause a packet
stuck problem.

The concurrent operations can be described as below,
         CPU 0                      |          CPU 1
   qdisc_run_end()                  |     qdisc_run_begin()
          .                         |           .
 ----> /* may be reorderd here */   |           .
|         .                         |           .
|     spin_unlock()                 |         set_bit()
|         .                         |         smp_mb__after_atomic()
 ---- test_bit()                    |         spin_trylock()
          .                         |          .

Consider the following sequence of events:
    CPU 0 reorder test_bit() ahead and see MISSED = 0
    CPU 1 calls set_bit()
    CPU 1 calls spin_trylock() and return fail
    CPU 0 executes spin_unlock()

At the end of the sequence, CPU 0 calls spin_unlock() and does nothing
because it see MISSED = 0. The skb on CPU 1 has beed enqueued but no one
take it, until the next cpu pushing to the qdisc (if ever ...) will
notice and dequeue it.

This patch fix this by adding one explicit barrier. As spin_unlock() and
test_bit() ordering is a store-load ordering, a full memory barrier
smp_mb() is needed here.

Fixes: a90c57f2cedd ("net: sched: fix packet stuck problem for lockless qdisc")
Signed-off-by: Guoju Fang 
Link: https://lore.kernel.org/r/20220528101628.120193-1-gjfang@linux.alibaba.com
Signed-off-by: Jakub Kicinski

net: sched: fixed barrier to prevent skbuff sticking in qdisc backlog

2022-05-27T03:45:46+00:00

In qdisc_run_begin(), smp_mb__before_atomic() used before test_bit()
does not provide any ordering guarantee as test_bit() is not an atomic
operation. This, added to the fact that the spin_trylock() call at
the beginning of qdisc_run_begin() does not guarantee acquire
semantics if it does not grab the lock, makes it possible for the
following statement :

if (test_bit(__QDISC_STATE_MISSED, &qdisc->state))

to be executed before an enqueue operation called before
qdisc_run_begin().

As a result the following race can happen :

           CPU 1                             CPU 2

      qdisc_run_begin()               qdisc_run_begin() /* true */
        set(MISSED)                            .
      /* returns false */                      .
          .                            /* sees MISSED = 1 */
          .                            /* so qdisc not empty */
          .                            __qdisc_run()
          .                                    .
          .                              pfifo_fast_dequeue()
 ----> /* may be done here */                  .
|         .                                clear(MISSED)
|         .                                    .
|         .                                smp_mb __after_atomic();
|         .                                    .
|         .                                /* recheck the queue */
|         .                                /* nothing => exit   */
|   enqueue(skb1)
|         .
|   qdisc_run_begin()
|         .
|     spin_trylock() /* fail */
|         .
|     smp_mb__before_atomic() /* not enough */
|         .
 ---- if (test_bit(MISSED))
        return false;   /* exit */

In the above scenario, CPU 1 and CPU 2 both try to grab the
qdisc->seqlock at the same time. Only CPU 2 succeeds and enters the
bypass code path, where it emits its skb then calls __qdisc_run().

CPU1 fails, sets MISSED and goes down the traditionnal enqueue() +
dequeue() code path. But when executing qdisc_run_begin() for the
second time, after enqueuing its skbuff, it sees the MISSED bit still
set (by itself) and consequently chooses to exit early without setting
it again nor trying to grab the spinlock again.

Meanwhile CPU2 has seen MISSED = 1, cleared it, checked the queue
and found it empty, so it returned.

At the end of the sequence, we end up with skb1 enqueued in the
backlog, both CPUs out of __dev_xmit_skb(), the MISSED bit not set,
and no __netif_schedule() called made. skb1 will now linger in the
qdisc until somebody later performs a full __qdisc_run(). Associated
to the bypass capacity of the qdisc, and the ability of the TCP layer
to avoid resending packets which it knows are still in the qdisc, this
can lead to serious traffic "holes" in a TCP connection.

We fix this by replacing the smp_mb__before_atomic() / test_bit() /
set_bit() / smp_mb__after_atomic() sequence inside qdisc_run_begin()
by a single test_and_set_bit() call, which is more concise and
enforces the needed memory barriers.

Fixes: 89837eb4b246 ("net: sched: add barrier to ensure correct ordering for lockless qdisc")
Signed-off-by: Vincent Ray 
Signed-off-by: Eric Dumazet 
Link: https://lore.kernel.org/r/20220526001746.2437669-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski

net: sched: remove qdisc_qlen_cpu()

2022-01-27T13:53:27+00:00

Never used since it was added in v5.2.

Signed-off-by: Jakub Kicinski 
Signed-off-by: David S. Miller

net_sched: restore "mpu xxx" handling

2022-01-13T19:06:42+00:00

commit 56b765b79e9a ("htb: improved accuracy at high rates") broke
"overhead X", "linklayer atm" and "mpu X" attributes.

"overhead X" and "linklayer atm" have already been fixed. This restores
the "mpu X" handling, as might be used by DOCSIS or Ethernet shaping:

    tc class add ... htb rate X overhead 4 mpu 64

The code being fixed is used by htb, tbf and act_police. Cake has its
own mpu handling. qdisc_calculate_pkt_len still uses the size table
containing values adjusted for mpu by user space.

iproute2 tc has always passed mpu into the kernel via a tc_ratespec
structure, but the kernel never directly acted on it, merely stored it
so that it could be read back by `tc class show`.

Rather, tc would generate length-to-time tables that included the mpu
(and linklayer) in their construction, and the kernel used those tables.

Since v3.7, the tables were no longer used. Along with "mpu", this also
broke "overhead" and "linklayer" which were fixed in 01cb71d2d47b
("net_sched: restore "overhead xxx" handling", v3.10) and 8a8e3d84b171
("net_sched: restore "linklayer atm" handling", v3.11).

"overhead" was fixed by simply restoring use of tc_ratespec::overhead -
this had originally been used by the kernel but was initially omitted
from the new non-table-based calculations.

"linklayer" had been handled in the table like "mpu", but the mode was
not originally passed in tc_ratespec. The new implementation was made to
handle it by getting new versions of tc to pass the mode in an extended
tc_ratespec, and for older versions of tc the table contents were analysed
at load time to deduce linklayer.

As "mpu" has always been given to the kernel in tc_ratespec,
accompanying the mpu-based table, we can restore system functionality
with no userspace change by making the kernel act on the tc_ratespec
value.

Fixes: 56b765b79e9a ("htb: improved accuracy at high rates")
Signed-off-by: Kevin Bracey 
Cc: Eric Dumazet 
Cc: Jiri Pirko 
Cc: Vimalkumar 
Link: https://lore.kernel.org/r/20220112170210.1014351-1-kevin@bracey.fi
Signed-off-by: Jakub Kicinski

Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

2021-12-24T00:09:58+00:00

include/net/sock.h
  commit 8f905c0e7354 ("inet: fully convert sk->sk_rx_dst to RCU rules")
  commit 43f51df41729 ("net: move early demux fields close to sk_refcnt")
  https://lore.kernel.org/all/20211222141641.0caa0ab3@canb.auug.org.au/

Signed-off-by: Jakub Kicinski