1. 08 Nov, 2017 8 commits
    • Kristian Evensen's avatar
      qmi_wwan: Add missing skb_reset_mac_header-call · 0de0add1
      Kristian Evensen authored
      When we receive a packet on a QMI device in raw IP mode, we should call
      skb_reset_mac_header() to ensure that skb->mac_header contains a valid
      offset in the packet. While it shouldn't really matter, the packets have
      no MAC header and the interface is configured as-such, it seems certain
      parts of the network stack expects a "good" value in skb->mac_header.
      
      Without the skb_reset_mac_header() call added in this patch, for example
      shaping traffic (using tc) triggers the following oops on the first
      received packet:
      
      [  303.642957] skbuff: skb_under_panic: text:8f137918 len:177 put:67 head:8e4b0f00 data:8e4b0eff tail:0x8e4b0fb0 end:0x8e4b1520 dev:wwan0
      [  303.655045] Kernel bug detected[#1]:
      [  303.658622] CPU: 1 PID: 1002 Comm: logd Not tainted 4.9.58 #0
      [  303.664339] task: 8fdf05e0 task.stack: 8f15c000
      [  303.668844] $ 0   : 00000000 00000001 0000007a 00000000
      [  303.674062] $ 4   : 8149a2fc 8149a2fc 8149ce20 00000000
      [  303.679284] $ 8   : 00000030 3878303a 31623465 20303235
      [  303.684510] $12   : ded731e3 2626a277 00000000 03bd0000
      [  303.689747] $16   : 8ef62b40 00000043 8f137918 804db5fc
      [  303.694978] $20   : 00000001 00000004 8fc13800 00000003
      [  303.700215] $24   : 00000001 8024ab10
      [  303.705442] $28   : 8f15c000 8fc19cf0 00000043 802cc920
      [  303.710664] Hi    : 00000000
      [  303.713533] Lo    : 74e58000
      [  303.716436] epc   : 802cc920 skb_panic+0x58/0x5c
      [  303.721046] ra    : 802cc920 skb_panic+0x58/0x5c
      [  303.725639] Status: 11007c03 KERNEL EXL IE
      [  303.729823] Cause : 50800024 (ExcCode 09)
      [  303.733817] PrId  : 0001992f (MIPS 1004Kc)
      [  303.737892] Modules linked in: rt2800pci rt2800mmio rt2800lib qcserial ppp_async option usb_wwan rt2x00pci rt2x00mmio rt2x00lib rndis_host qmi_wwan ppp_generic nf_nat_pptp nf_conntrack_pptp nf_conntrack_ipv6 mt76x2i
      Process logd (pid: 1002, threadinfo=8f15c000, task=8fdf05e0, tls=77b3eee4)
      [  303.962509] Stack : 00000000 80408990 8f137918 000000b1 00000043 8e4b0f00 8e4b0eff 8e4b0fb0
      [  303.970871]         8e4b1520 8fec1800 00000043 802cd2a4 6e000045 00000043 00000000 8ef62000
      [  303.979219]         8eef5d00 8ef62b40 8fea7300 8f137918 00000000 00000000 0002bb01 793e5664
      [  303.987568]         8ef08884 00000001 8fea7300 00000002 8fc19e80 8eef5d00 00000006 00000003
      [  303.995934]         00000000 8030ba90 00000003 77ab3fd0 8149dc80 8004d1bc 8f15c000 8f383700
      [  304.004324]         ...
      [  304.006767] Call Trace:
      [  304.009241] [<802cc920>] skb_panic+0x58/0x5c
      [  304.013504] [<802cd2a4>] skb_push+0x78/0x90
      [  304.017783] [<8f137918>] 0x8f137918
      [  304.021269] Code: 00602825  0c02a3b4  24842888 <000c000d> 8c870060  8c8200a0  0007382b  00070336  8c88005c
      [  304.031034]
      [  304.032805] ---[ end trace b778c482b3f0bda9 ]---
      [  304.041384] Kernel panic - not syncing: Fatal exception in interrupt
      [  304.051975] Rebooting in 3 seconds..
      
      While the oops is for a 4.9-kernel, I was able to trigger the same oops with
      net-next as of yesterday.
      
      Fixes: 32f7adf6 ("net: qmi_wwan: support "raw IP" mode")
      Signed-off-by: default avatarKristian Evensen <kristian.evensen@gmail.com>
      Acked-by: default avatarBjørn Mork <bjorn@mork.no>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      0de0add1
    • Jay Vosburgh's avatar
      bonding: fix slave stuck in BOND_LINK_FAIL state · 055db695
      Jay Vosburgh authored
      The bonding miimon logic has a flaw, in that a failure of the
      rtnl_trylock can cause a slave to become permanently stuck in
      BOND_LINK_FAIL state.
      
      	The sequence of events to cause this is as follows:
      
      	1) bond_miimon_inspect finds that a slave's link is down, and so
      calls bond_propose_link_state, setting slave->new_link_state to
      BOND_LINK_FAIL, then sets slave->new_link to BOND_LINK_DOWN and returns
      non-zero.
      
      	2) In bond_mii_monitor, the rtnl_trylock fails, and the timer is
      rescheduled.  No change is committed.
      
      	3) bond_miimon_inspect is called again, but this time the slave
      from step 1 has recovered.  slave->new_link is reset to NOCHANGE, and, as
      slave->link was never changed, the switch enters the BOND_LINK_UP case,
      and does nothing.  The pending BOND_LINK_FAIL state from step 1 remains
      pending, as new_link_state is not reset.
      
      	4) The state from step 3 persists until another slave changes link
      state and causes bond_miimon_inspect to return non-zero.  At this point,
      the BOND_LINK_FAIL state change on the slave from steps 1-3 is committed,
      and the slave will remain stuck in BOND_LINK_FAIL state even though it
      is actually link up.
      
      	The remedy for this is to initialize new_link_state on each entry
      to bond_miimon_inspect, as is already done with new_link.
      
      Fixes: fb9eb899 ("bonding: handle link transition from FAIL to UP correctly")
      Reported-by: default avatarAlex Sidorenko <alexandre.sidorenko@hpe.com>
      Reviewed-by: default avatarJarod Wilson <jarod@redhat.com>
      Signed-off-by: default avatarJay Vosburgh <jay.vosburgh@canonical.com>
      Acked-by: default avatarMahesh Bandewar <maheshb@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      055db695
    • Bjorn Andersson's avatar
      qrtr: Move to postcore_initcall · b7e732fa
      Bjorn Andersson authored
      Registering qrtr with module_init makes the ability of typical platform
      code to create AF_QIPCRTR socket during probe a matter of link order
      luck. Moving qrtr to postcore_initcall() avoids this.
      Signed-off-by: default avatarBjorn Andersson <bjorn.andersson@linaro.org>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      b7e732fa
    • Bjørn Mork's avatar
      net: qmi_wwan: fix divide by 0 on bad descriptors · 7fd07833
      Bjørn Mork authored
      A CDC Ethernet functional descriptor with wMaxSegmentSize = 0 will
      cause a divide error in usbnet_probe:
      
      divide error: 0000 [#1] PREEMPT SMP KASAN
      Modules linked in:
      CPU: 0 PID: 24 Comm: kworker/0:1 Not tainted 4.14.0-rc8-44453-g1fdc1a82c34f #56
      Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
      Workqueue: usb_hub_wq hub_event
      task: ffff88006bef5c00 task.stack: ffff88006bf60000
      RIP: 0010:usbnet_update_max_qlen+0x24d/0x390 drivers/net/usb/usbnet.c:355
      RSP: 0018:ffff88006bf67508 EFLAGS: 00010246
      RAX: 00000000000163c8 RBX: ffff8800621fce40 RCX: ffff8800621fcf34
      RDX: 0000000000000000 RSI: ffffffff837ecb7a RDI: ffff8800621fcf34
      RBP: ffff88006bf67520 R08: ffff88006bef5c00 R09: ffffed000c43f881
      R10: ffffed000c43f880 R11: ffff8800621fc406 R12: 0000000000000003
      R13: ffffffff85c71de0 R14: 0000000000000000 R15: 0000000000000000
      FS:  0000000000000000(0000) GS:ffff88006ca00000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 00007ffe9c0d6dac CR3: 00000000614f4000 CR4: 00000000000006f0
      Call Trace:
       usbnet_probe+0x18b5/0x2790 drivers/net/usb/usbnet.c:1783
       qmi_wwan_probe+0x133/0x220 drivers/net/usb/qmi_wwan.c:1338
       usb_probe_interface+0x324/0x940 drivers/usb/core/driver.c:361
       really_probe drivers/base/dd.c:413
       driver_probe_device+0x522/0x740 drivers/base/dd.c:557
      
      Fix by simply ignoring the bogus descriptor, as it is optional
      for QMI devices anyway.
      
      Fixes: 423ce8ca ("net: usb: qmi_wwan: New driver for Huawei QMI based WWAN devices")
      Reported-by: default avatarAndrey Konovalov <andreyknvl@google.com>
      Signed-off-by: default avatarBjørn Mork <bjorn@mork.no>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      7fd07833
    • Bjørn Mork's avatar
      net: cdc_ether: fix divide by 0 on bad descriptors · 2cb80187
      Bjørn Mork authored
      Setting dev->hard_mtu to 0 will cause a divide error in
      usbnet_probe. Protect against devices with bogus CDC Ethernet
      functional descriptors by ignoring a zero wMaxSegmentSize.
      Signed-off-by: default avatarBjørn Mork <bjorn@mork.no>
      Acked-by: default avatarOliver Neukum <oneukum@suse.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      2cb80187
    • Hangbin Liu's avatar
      bonding: discard lowest hash bit for 802.3ad layer3+4 · b5f86218
      Hangbin Liu authored
      After commit 07f4c900 ("tcp/dccp: try to not exhaust ip_local_port_range
      in connect()"), we will try to use even ports for connect(). Then if an
      application (seen clearly with iperf) opens multiple streams to the same
      destination IP and port, each stream will be given an even source port.
      
      So the bonding driver's simple xmit_hash_policy based on layer3+4 addressing
      will always hash all these streams to the same interface. And the total
      throughput will limited to a single slave.
      
      Change the tcp code will impact the whole tcp behavior, only for bonding
      usage. Paolo Abeni suggested fix this by changing the bonding code only,
      which should be more reasonable, and less impact.
      
      Fix this by discarding the lowest hash bit because it contains little entropy.
      After the fix we can re-balance between slaves.
      Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
      Signed-off-by: default avatarHangbin Liu <liuhangbin@gmail.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      b5f86218
    • Gustavo A. R. Silva's avatar
      net/mlx5e/core/en_fs: fix pointer dereference after free in mlx5e_execute_l2_action · 39a4b86f
      Gustavo A. R. Silva authored
      hn is being kfree'd in mlx5e_del_l2_from_hash and then dereferenced
      by accessing hn->ai.addr
      
      Fix this by copying the MAC address into a local variable for its safe use
      in all possible execution paths within function mlx5e_execute_l2_action.
      
      Addresses-Coverity-ID: 1417789
      Fixes: eeb66cdb ("net/mlx5: Separate between E-Switch and MPFS")
      Signed-off-by: default avatarGustavo A. R. Silva <garsilva@embeddedor.com>
      Acked-by: default avatarSaeed Mahameed <saeedm@mellanox.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      39a4b86f
    • Marc Zyngier's avatar
      net: mvpp2: Prevent userspace from changing TX affinities · 13c249a9
      Marc Zyngier authored
      The mvpp2 driver can't cope at all with the TX affinities being
      changed from userspace, and spit an endless stream of
      
      [   91.779920] mvpp2 f4000000.ethernet eth2: wrong cpu on the end of Tx processing
      [   91.779930] mvpp2 f4000000.ethernet eth2: wrong cpu on the end of Tx processing
      [   91.780402] mvpp2 f4000000.ethernet eth2: wrong cpu on the end of Tx processing
      [   91.780406] mvpp2 f4000000.ethernet eth2: wrong cpu on the end of Tx processing
      [   91.780415] mvpp2 f4000000.ethernet eth2: wrong cpu on the end of Tx processing
      [   91.780418] mvpp2 f4000000.ethernet eth2: wrong cpu on the end of Tx processing
      
      rendering the box completely useless (I've measured around 600k
      interrupts/s on a 8040 box) once irqbalance kicks in and start
      doing its job.
      
      Obviously, the driver was never designed with this in mind. So let's
      work around the problem by preventing userspace from interacting
      with these interrupts altogether.
      Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      13c249a9
  2. 05 Nov, 2017 2 commits
    • Priyaranjan Jha's avatar
      tcp: fix DSACK-based undo on non-duplicate ACK · d09b9e60
      Priyaranjan Jha authored
      Fixes DSACK-based undo when sender is in Open State and
      an ACK advances snd_una.
      
      Example scenario:
      - Sender goes into recovery and makes some spurious rtx.
      - It comes out of recovery and enters into open state.
      - It sends some more packets, let's say 4.
      - The receiver sends an ACK for the first two, but this ACK is lost.
      - The sender receives ack for first two, and DSACK for previous
        spurious rtx.
      Signed-off-by: default avatarPriyaranjan Jha <priyarjha@google.com>
      Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
      Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
      Acked-by: default avatarYousuk Seung <ysseung@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      d09b9e60
    • Guillaume Nault's avatar
      l2tp: don't use l2tp_tunnel_find() in l2tp_ip and l2tp_ip6 · 8f7dc9ae
      Guillaume Nault authored
      Using l2tp_tunnel_find() in l2tp_ip_recv() is wrong for two reasons:
      
        * It doesn't take a reference on the returned tunnel, which makes the
          call racy wrt. concurrent tunnel deletion.
      
        * The lookup is only based on the tunnel identifier, so it can return
          a tunnel that doesn't match the packet's addresses or protocol.
      
      For example, a packet sent to an L2TPv3 over IPv6 tunnel can be
      delivered to an L2TPv2 over UDPv4 tunnel. This is worse than a simple
      cross-talk: when delivering the packet to an L2TP over UDP tunnel, the
      corresponding socket is UDP, where ->sk_backlog_rcv() is NULL. Calling
      sk_receive_skb() will then crash the kernel by trying to execute this
      callback.
      
      And l2tp_tunnel_find() isn't even needed here. __l2tp_ip_bind_lookup()
      properly checks the socket binding and connection settings. It was used
      as a fallback mechanism for finding tunnels that didn't have their data
      path registered yet. But it's not limited to this case and can be used
      to replace l2tp_tunnel_find() in the general case.
      
      Fix l2tp_ip6 in the same way.
      
      Fixes: 0d76751f ("l2tp: Add L2TPv3 IP encapsulation (no UDP) support")
      Fixes: a32e0eec ("l2tp: introduce L2TPv3 IP encapsulation support for IPv6")
      Signed-off-by: default avatarGuillaume Nault <g.nault@alphalink.fr>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      8f7dc9ae
  3. 04 Nov, 2017 3 commits
    • Andrey Konovalov's avatar
      net: usb: asix: fill null-ptr-deref in asix_suspend · baedf68a
      Andrey Konovalov authored
      When asix_suspend() is called dev->driver_priv might not have been
      assigned a value, so we need to check that it's not NULL.
      
      Found by syzkaller.
      
      kasan: CONFIG_KASAN_INLINE enabled
      kasan: GPF could be caused by NULL-ptr deref or user memory access
      general protection fault: 0000 [#1] PREEMPT SMP KASAN
      Modules linked in:
      CPU: 0 PID: 24 Comm: kworker/0:1 Not tainted 4.14.0-rc4-43422-geccacdd69a8c #400
      Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
      Workqueue: usb_hub_wq hub_event
      task: ffff88006bb36300 task.stack: ffff88006bba8000
      RIP: 0010:asix_suspend+0x76/0xc0 drivers/net/usb/asix_devices.c:629
      RSP: 0018:ffff88006bbae718 EFLAGS: 00010202
      RAX: dffffc0000000000 RBX: ffff880061ba3b80 RCX: 1ffff1000c34d644
      RDX: 0000000000000001 RSI: 0000000000000402 RDI: 0000000000000008
      RBP: ffff88006bbae738 R08: 1ffff1000d775cad R09: 0000000000000000
      R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800630a8b40
      R13: 0000000000000000 R14: 0000000000000402 R15: ffff880061ba3b80
      FS:  0000000000000000(0000) GS:ffff88006c600000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 00007ff33cf89000 CR3: 0000000061c0a000 CR4: 00000000000006f0
      Call Trace:
       usb_suspend_interface drivers/usb/core/driver.c:1209
       usb_suspend_both+0x27f/0x7e0 drivers/usb/core/driver.c:1314
       usb_runtime_suspend+0x41/0x120 drivers/usb/core/driver.c:1852
       __rpm_callback+0x339/0xb60 drivers/base/power/runtime.c:334
       rpm_callback+0x106/0x220 drivers/base/power/runtime.c:461
       rpm_suspend+0x465/0x1980 drivers/base/power/runtime.c:596
       __pm_runtime_suspend+0x11e/0x230 drivers/base/power/runtime.c:1009
       pm_runtime_put_sync_autosuspend ./include/linux/pm_runtime.h:251
       usb_new_device+0xa37/0x1020 drivers/usb/core/hub.c:2487
       hub_port_connect drivers/usb/core/hub.c:4903
       hub_port_connect_change drivers/usb/core/hub.c:5009
       port_event drivers/usb/core/hub.c:5115
       hub_event+0x194d/0x3740 drivers/usb/core/hub.c:5195
       process_one_work+0xc7f/0x1db0 kernel/workqueue.c:2119
       worker_thread+0x221/0x1850 kernel/workqueue.c:2253
       kthread+0x3a1/0x470 kernel/kthread.c:231
       ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
      Code: 8d 7c 24 20 48 89 fa 48 c1 ea 03 80 3c 02 00 75 5b 48 b8 00 00
      00 00 00 fc ff df 4d 8b 6c 24 20 49 8d 7d 08 48 89 fa 48 c1 ea 03 <80>
      3c 02 00 75 34 4d 8b 6d 08 4d 85 ed 74 0b e8 26 2b 51 fd 4c
      RIP: asix_suspend+0x76/0xc0 RSP: ffff88006bbae718
      ---[ end trace dfc4f5649284342c ]---
      Signed-off-by: default avatarAndrey Konovalov <andreyknvl@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      baedf68a
    • Ye Yin's avatar
      netfilter/ipvs: clear ipvs_property flag when SKB net namespace changed · 2b5ec1a5
      Ye Yin authored
      When run ipvs in two different network namespace at the same host, and one
      ipvs transport network traffic to the other network namespace ipvs.
      'ipvs_property' flag will make the second ipvs take no effect. So we should
      clear 'ipvs_property' when SKB network namespace changed.
      
      Fixes: 621e84d6 ("dev: introduce skb_scrub_packet()")
      Signed-off-by: default avatarYe Yin <hustcat@gmail.com>
      Signed-off-by: default avatarWei Zhou <chouryzhou@gmail.com>
      Signed-off-by: default avatarJulian Anastasov <ja@ssi.bg>
      Signed-off-by: default avatarSimon Horman <horms@verge.net.au>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      2b5ec1a5
    • Ganesh Goudar's avatar
      cxgb4: update latest firmware version supported · 24de79e5
      Ganesh Goudar authored
      Change t4fw_version.h to update latest firmware version
      number to 1.16.63.0.
      Signed-off-by: default avatarGanesh Goudar <ganeshgr@chelsio.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      24de79e5
  4. 03 Nov, 2017 25 commits
  5. 02 Nov, 2017 2 commits
    • Madhavan Srinivasan's avatar
      powerpc/perf: Fix core-imc hotplug callback failure during imc initialization · 7ecb37f6
      Madhavan Srinivasan authored
      Call trace observed during boot:
      
        nest_capp0_imc performance monitor hardware support registered
        nest_capp1_imc performance monitor hardware support registered
        core_imc memory allocation for cpu 56 failed
        Unable to handle kernel paging request for data at address 0xffa400010
        Faulting instruction address: 0xc000000000bf3294
        0:mon> e
        cpu 0x0: Vector: 300 (Data Access) at [c000000ff38ff8d0]
            pc: c000000000bf3294: mutex_lock+0x34/0x90
            lr: c000000000bf3288: mutex_lock+0x28/0x90
            sp: c000000ff38ffb50
           msr: 9000000002009033
           dar: ffa400010
         dsisr: 80000
          current = 0xc000000ff383de00
          paca    = 0xc000000007ae0000	 softe: 0	 irq_happened: 0x01
            pid   = 13, comm = cpuhp/0
        Linux version 4.11.0-39.el7a.ppc64le (mockbuild@ppc-058.build.eng.bos.redhat.com) (gcc version 4.8.5 20150623 (Red Hat 4.8.5-16) (GCC) ) #1 SMP Tue Oct 3 07:42:44 EDT 2017
        0:mon> t
        [c000000ff38ffb80] c0000000002ddfac perf_pmu_migrate_context+0xac/0x470
        [c000000ff38ffc40] c00000000011385c ppc_core_imc_cpu_offline+0x1ac/0x1e0
        [c000000ff38ffc90] c000000000125758 cpuhp_invoke_callback+0x198/0x5d0
        [c000000ff38ffd00] c00000000012782c cpuhp_thread_fun+0x8c/0x3d0
        [c000000ff38ffd60] c0000000001678d0 smpboot_thread_fn+0x290/0x2a0
        [c000000ff38ffdc0] c00000000015ee78 kthread+0x168/0x1b0
        [c000000ff38ffe30] c00000000000b368 ret_from_kernel_thread+0x5c/0x74
      
      While registering the cpuhoplug callbacks for core-imc, if we fails
      in the cpuhotplug online path for any random core (either because opal call to
      initialize the core-imc counters fails or because memory allocation fails for
      that core), ppc_core_imc_cpu_offline() will get invoked for other cpus who
      successfully returned from cpuhotplug online path.
      
      But in the ppc_core_imc_cpu_offline() path we are trying to migrate the event
      context, when core-imc counters are not even initialized. Thus creating the
      above stack dump.
      
      Add a check to see if core-imc counters are enabled or not in the cpuhotplug
      offline path before migrating the context to handle this failing scenario.
      
      Fixes: 885dcd70 ("powerpc/perf: Add nest IMC PMU support")
      Signed-off-by: default avatarMadhavan Srinivasan <maddy@linux.vnet.ibm.com>
      Signed-off-by: default avatarAnju T Sudhakar <anju@linux.vnet.ibm.com>
      Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
      7ecb37f6
    • Linus Torvalds's avatar
      Kbuild: don't pass "-C" to preprocessor when processing linker scripts · 5cb0512c
      Linus Torvalds authored
      For some odd historical reason, we preprocessed the linker scripts with
      "-C", which keeps comments around.  That makes no sense, since the
      comments are not meaningful for the build anyway.
      
      And it actually breaks things, since linker scripts can't have C++ style
      "//" comments in them, so keeping comments after preprocessing now
      limits us in odd and surprising ways in our header files for no good
      reason.
      
      The -C option goes back to pre-git and pre-bitkeeper times, but seems to
      have been historically used (along with "-traditional") for some
      odd-ball architectures (ia64, MIPS and SH).  It probably didn't matter
      back then either, but might possibly have been used to minimize the
      difference between the original file and the pre-processed result.
      
      The reason for this may be lost in time, but let's not perpetuate it
      only because we can't remember why we did this crazy thing.
      
      This was triggered by the recent addition of SPDX lines to the source
      tree, where people apparently were confused about why header files
      couldn't use the C++ comment format.
      
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Greg KH <gregkh@linuxfoundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      5cb0512c