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Vladimir Oltean 29d98f54a4 net: enetc: allow hardware timestamping on TX queues with tc-etf enabled 
The txtime is passed to the driver in skb->skb_mstamp_ns, which is
actually in a union with skb->tstamp (the place where software
timestamps are kept).

Since commit b50a5c70ff ("net: allow simultaneous SW and HW transmit
timestamping"), __sock_recv_timestamp has some logic for making sure
that the two calls to skb_tstamp_tx:

skb_tx_timestamp(skb) # Software timestamp in the driver
-> skb_tstamp_tx(skb, NULL)

and

skb_tstamp_tx(skb, &shhwtstamps) # Hardware timestamp in the driver

will both do the right thing and in a race-free manner, meaning that
skb_tx_timestamp will deliver a cmsg with the software timestamp only,
and skb_tstamp_tx with a non-NULL hwtstamps argument will deliver a cmsg
with the hardware timestamp only.

Why are races even possible? Well, because although the software timestamp
skb->tstamp is private per skb, the hardware timestamp skb_hwtstamps(skb)
lives in skb_shinfo(skb), an area which is shared between skbs and their
clones. And skb_tstamp_tx works by cloning the packets when timestamping
them, therefore attempting to perform hardware timestamping on an skb's
clone will also change the hardware timestamp of the original skb. And
the original skb might have been yet again cloned for software
timestamping, at an earlier stage.

So the logic in __sock_recv_timestamp can't be as simple as saying
"does this skb have a hardware timestamp? if yes I'll send the hardware
timestamp to the socket, otherwise I'll send the software timestamp",
precisely because the hardware timestamp is shared.
Instead, it's quite the other way around: __sock_recv_timestamp says
"does this skb have a software timestamp? if yes, I'll send the software
timestamp, otherwise the hardware one". This works because the software
timestamp is not shared with clones.

But that means we have a problem when we attempt hardware timestamping
with skbs that don't have the skb->tstamp == 0. __sock_recv_timestamp
will say "oh, yeah, this must be some sort of odd clone" and will not
deliver the hardware timestamp to the socket. And this is exactly what
is happening when we have txtime enabled on the socket: as mentioned,
that is put in a union with skb->tstamp, so it is quite easy to mistake
it.

Do what other drivers do (intel igb/igc) and write zero to skb->tstamp
before taking the hardware timestamp. It's of no use to us now (we're
already on the TX confirmation path).

Fixes: 0d08c9ec7d ("enetc: add support time specific departure base on the qos etf")
Cc: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2021-03-08 12:03:42 -08:00
arch Merge https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf 2021-02-26 13:16:31 -08:00
block for-5.12/block-ipi-2021-02-21 2021-02-22 10:53:05 -08:00
certs certs: Replace K{U,G}IDT_INIT() with GLOBAL_ROOT_{U,G}ID 2021-01-21 16:16:10 +00:00
crypto Keyrings miscellany 2021-02-23 16:09:23 -08:00
Documentation docs: networking: drop special stable handling 2021-03-03 08:49:08 -08:00
drivers net: enetc: allow hardware timestamping on TX queues with tc-etf enabled 2021-03-08 12:03:42 -08:00
fs Miscellaneous ext4 cleanups and bug fixes. Pretty boring this 2021-02-25 10:06:55 -08:00
include Merge git://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf 2021-03-06 17:02:40 -08:00
init Kbuild updates for v5.12 2021-02-25 10:17:31 -08:00
ipc fs: make helpers idmap mount aware 2021-01-24 14:27:20 +01:00
kernel bpf: Explicitly zero-extend R0 after 32-bit cmpxchg 2021-03-04 19:06:03 -08:00
lib Kbuild updates for v5.12 2021-02-25 10:17:31 -08:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm mm/hugetlb: change hugetlb_reserve_pages() to type bool 2021-02-24 13:38:35 -08:00
net net: dsa: fix switchdev objects on bridge master mistakenly being applied on ports 2021-03-08 11:59:00 -08:00
samples samples, bpf: Add missing munmap in xdpsock 2021-03-04 15:53:32 +01:00
scripts Kbuild updates for v5.12 2021-02-25 10:17:31 -08:00
security Keyrings miscellany 2021-02-23 16:09:23 -08:00
sound ARM updates for 5.12-rc1: 2021-02-22 14:27:07 -08:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf 2021-03-06 17:02:40 -08:00
usr Kbuild updates for v5.12 2021-02-25 10:17:31 -08:00
virt KVM/arm64 fixes for 5.11, take #2 2021-02-12 14:07:39 +00:00
.clang-format cxl for 5.12 2021-02-24 09:38:36 -08:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore clang-lto series for v5.12-rc1 2021-02-23 09:28:51 -08:00
.mailmap Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-02-21 17:23:56 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS CREDITS: update email address and home address 2021-01-27 21:03:50 +02:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS wireless-drivers fixes for v5.12 2021-02-26 13:17:44 -08:00
Makefile Kbuild updates for v5.12 2021-02-25 10:17:31 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.