This is a 32-bit register. Apparently harmless on real hardware, but
causing justified warnings in simulation.
Signed-off-by: CQ Tang <cq.tang@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: stable@vger.kernel.org

Holding mm_users works OK for graphics, which was the first user of SVM
with VT-d. However, it works less well for other devices, where we actually
do a mmap() from the file descriptor to which the SVM PASID state is tied.

In this case on process exit we end up with a recursive reference count:
 - The MM remains alive until the file is closed and the driver's release()
   call ends up unbinding the PASID.
 - The VMA corresponding to the mmap() remains intact until the MM is
   destroyed.
 - Thus the file isn't closed, even when exit_files() runs, because the
   VMA is still holding a reference to it. And the MM remains alive…

To address this issue, we *stop* holding mm_users while the PASID is bound.
We already hold mm_count by virtue of the MMU notifier, and that can be
made to be sufficient.

It means that for a period during process exit, the fun part of mmput()
has happened and exit_mmap() has been called so the MM is basically
defunct. But the PGD still exists and the PASID is still bound to it.

During this period, we have to be very careful — exit_mmap() doesn't use
mm->mmap_sem because it doesn't expect anyone else to be touching the MM
(quite reasonably, since mm_users is zero). So we also need to fix the
fault handler to just report failure if mm_users is already zero, and to
temporarily bump mm_users while handling any faults.

Additionally, exit_mmap() calls mmu_notifier_release() *before* it tears
down the page tables, which is too early for us to flush the IOTLB for
this PASID. And __mmu_notifier_release() removes every notifier from the
list, so when exit_mmap() finally *does* tear down the mappings and
clear the page tables, we don't get notified. So we work around this by
clearing the PASID table entry in our MMU notifier release() callback.
That way, the hardware *can't* get any pages back from the page tables
before they get cleared.

Hardware designers have confirmed that the resulting 'PASID not present'
faults should be handled just as gracefully as 'page not present' faults,
the important criterion being that they don't perturb the operation for
any *other* PASID in the system.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: stable@vger.kernel.org

Pull SCSI fix from James Bottomley:
 "A single fix for machines with pages > 4k (PPC mostly).

  There's a bug in our optimal transfer size code where we don't account
  for pages > 4k and can set the transfer size to be less than the page
  size causing nasty failures"

* tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
  sd: Reject optimal transfer length smaller than page size

Pull PCI fixlet from Bjorn Helgaas:
 "This marks the TI DRA7xx host bridge driver as broken.  Apparently it
  has never worked without some additional out-of-tree code, so I'm
  going to mark it broken now and remove it completely next cycle unless
  it's fixed"

* tag 'pci-v4.4-fixes-4' of git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci:
  PCI: dra7xx: Mark driver as broken

kernel test robot has reported the following crash:

  BUG: unable to handle kernel NULL pointer dereference at 00000100
  IP: [<c1074df6>] __queue_work+0x26/0x390
  *pdpt = 0000000000000000 *pde = f000ff53f000ff53 *pde = f000ff53f000ff53
  Oops: 0000 [#1] PREEMPT PREEMPT SMP SMP
  CPU: 0 PID: 24 Comm: kworker/0:1 Not tainted 4.4.0-rc4-00139-g373ccbe5 #1
  Workqueue: events vmstat_shepherd
  task: cb684600 ti: cb7ba000 task.ti: cb7ba000
  EIP: 0060:[<c1074df6>] EFLAGS: 00010046 CPU: 0
  EIP is at __queue_work+0x26/0x390
  EAX: 00000046 EBX: cbb37800 ECX: cbb37800 EDX: 00000000
  ESI: 00000000 EDI: 00000000 EBP: cb7bbe68 ESP: cb7bbe38
   DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
  CR0: 8005003b CR2: 00000100 CR3: 01fd5000 CR4: 000006b0
  Stack:
  Call Trace:
    __queue_delayed_work+0xa1/0x160
    queue_delayed_work_on+0x36/0x60
    vmstat_shepherd+0xad/0xf0
    process_one_work+0x1aa/0x4c0
    worker_thread+0x41/0x440
    kthread+0xb0/0xd0
    ret_from_kernel_thread+0x21/0x40

The reason is that start_shepherd_timer schedules the shepherd work item
which uses vmstat_wq (vmstat_shepherd) before setup_vmstat allocates
that workqueue so if the further initialization takes more than HZ we
might end up scheduling on a NULL vmstat_wq.  This is really unlikely
but not impossible.

Fixes: 373ccbe5 ("mm, vmstat: allow WQ concurrency to discover memory reclaim doesn't make any progress")
Reported-by: kernel test robot <ying.huang@linux.intel.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Tested-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: stable@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Pull ARM SoC fixes from Arnd Bergmann:
 "This is the final small set of ARM SoC bug fixes for linux-4.4, almost
  all regressions:

  OMAP:
   - data corruption on the Nokia N900 flash

  Allwinner:
   - Two defconfig change to get USB working again

  ARM Versatile:
   - Interrupt numbers gone bad after an older bug fix

  Nomadik:
   - Crashes from incorrect L2 cache settings

  VIA vt8500:
   - SD/MMC support on WM8650 never worked"

* tag 'fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc:
  dts: vt8500: Add SDHC node to DTS file for WM8650
  ARM: Fix broken USB support in multi_v7_defconfig for sunxi devices
  ARM: versatile: fix MMC/SD interrupt assignment
  ARM: nomadik: set latencies to 8 cycles
  ARM: OMAP2+: Fix onenand rate detection to avoid filesystem corruption
  ARM: Fix broken USB support in sunxi_defconfig

Pull KVM fix from Paolo Bonzini:
 "A simple fix.  I'm sending it before the merge window, because it
  refines a patch found in your master branch but not yet in the
  kvm/next branch that is destined for 4.5"

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  kvm: x86: only channel 0 of the i8254 is linked to the HPET

Pull ACPI fix from Rafael Wysocki:
 "Just one obvious fix that adds a missing function argument in ACPI
  code introduced recently (Kees Cook)"

* tag 'pm+acpi-4.4-final' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  ACPI / property: avoid leaking format string into kobject name

Pull x86 fixes from Ingo Molnar:
 "A handful of x86 fixes:

   - a syscall ABI fix, fixing an Android breakage
   - a Xen PV guest fix relating to the RTC device, causing a
     non-working console
   - a Xen guest syscall stack frame fix
   - an MCE hotplug CPU crash fix"

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/numachip: Fix NumaConnect2 MMCFG PCI access
  x86/entry: Restore traditional SYSENTER calling convention
  x86/entry: Fix some comments
  x86/paravirt: Prevent rtc_cmos platform device init on PV guests
  x86/xen: Avoid fast syscall path for Xen PV guests
  x86/mce: Ensure offline CPUs don't participate in rendezvous process

Pull scheduler fixes from Ingo Molnar:
 "Misc scheduler fixes"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/core: Reset task's lockless wake-queues on fork()
  sched/core: Fix unserialized r-m-w scribbling stuff
  sched/core: Check tgid in is_global_init()
  sched/fair: Fix multiplication overflow on 32-bit systems

Pull perf fixes from Ingo Molnar:
 "Two core subsystem fixes, plus a handful of tooling fixes"

* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf: Fix race in swevent hash
  perf: Fix race in perf_event_exec()
  perf list: Robustify event printing routine
  perf list: Add support for PERF_COUNT_SW_BPF_OUT
  perf hists browser: Fix segfault if use symbol filter in cmdline
  perf hists browser: Reset selection when refresh
  perf hists browser: Add NULL pointer check to prevent crash
  perf buildid-list: Fix return value of perf buildid-list -k
  perf buildid-list: Show running kernel build id fix

Pull irq fix from Ingo Molnar:
 "Fixes a core IRQ subsystem deadlock"

* 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  genirq: Prevent chip buslock deadlock

Pull block revert from Jens Axboe:
 "The previous pull request had a split fix for NVMe, however there are
  corner cases where that ends up blowing up.

  So let's revert it for 4.4.  The regression isn't introduced in this
  cycle, and it's "just" a performance regression, not a
  stability/integrity issue"

* 'for-linus' of git://git.kernel.dk/linux-block:
  Revert "block: Split bios on chunk boundaries"

Pull dmaengine fixes from Vinod Koul:
 "Late fixes for 4.4 are three fixes for drivers which include a revert
  of mic-x100 fix which is causing regression, xgene fix for double IRQ
  and async_tx fix to use GFP_NOWAIT"

* tag 'dmaengine-fix-4.4' of git://git.infradead.org/users/vkoul/slave-dma:
  dmaengine: xgene-dma: Fix double IRQ issue by setting IRQ_DISABLE_UNLAZY flag
  async_tx: use GFP_NOWAIT rather than GFP_IO
  dmaengine: Revert "dmaengine: mic_x100: add missing spin_unlock"

Pull dmi fix from Jean Delvare.

* 'dmi-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jdelvare/staging:
  firmware: dmi_scan: Fix UUID endianness for SMBIOS >= 2.6

Pull sound fixes from Takashi Iwai:
 "A slightly higher volume than a new year's wish, but not too
  worrisome: a large LOC is only for HD-audio device-specific quirks, so
  fairly safe to apply.  The rest ASoC fixes are all trivial and small;
  a simple replacement of mutex call with nested lock version, a few
  Arizona and Realtek codec fixes, and a regression fix for Skylake
  firmware handling"

* tag 'sound-4.4' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound:
  ASoC: Intel: Skylake: Fix the memory leak
  ASoC: Intel: Skylake: Revert previous broken fix memory leak fix
  ASoC: Use nested lock for snd_soc_dapm_mutex_lock
  ASoC: rt5645: add sys clk detection
  ALSA: hda - Add keycode map for alc input device
  ALSA: hda - Add mic mute hotkey quirk for Lenovo ThinkCentre AIO
  ASoC: arizona: Fix bclk for sample rates that are multiple of 4kHz

Merge tag 'omap-for-v4.4/onenand-corruption' of git://git.kernel.org/pub/scm/linux/kernel/git/tmlind/linux-omap into fixes

Pull "urgent onenand file system corruption fix for n900" from Tony Lindgren:

Last minute urgent pull request to prevent file system corruption
on Nokia N900.

Looks like we have a GPMC bus timing bug that has gone unnoticed
because of bootloader configured registers until few days ago. We
are not detecting the onenand clock rate properly unless we have
CONFIG_OMAP_GPMC_DEBUG set and this causes onenand corruption
that can be easily be reproduced.

There seems to be also an additional bug still lurking around for
onenand corruption. But that is still being investigated and
it does not seem to be GPMC timings related.

Meanwhile, it would be good to get this fix into v4.4 to prevent
wrong timings from corrupting onenand.

* tag 'omap-for-v4.4/onenand-corruption' of git://git.kernel.org/pub/scm/linux/kernel/git/tmlind/linux-omap:
  ARM: OMAP2+: Fix onenand rate detection to avoid filesystem corruption

This reverts commit d3805611.

If we end up splitting on the first segment, we don't adjust
the sector count. That results in hitting a BUG() with attempting
to split 0 sectors.

As this is just a performance issue and not a regression since
4.3 release, let's just rever this change. That gives us more
time to test a real fix for 4.5, which would be marked for
stable anyway.

Mark the dra7xx PCI host driver as broken.  This driver was first merged in
v3.17 and has never worked.  Although the driver compiles just fine, it is
missing an essential device reset.  If the driver is included, the kernel
locks up hard shortly after booting, before any console output appears.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

The dmi_ver wasn't updated correctly before the dmi_decode method run
to save the uuid.

That resulted in "dmidecode -s system-uuid" and
/sys/class/dmi/id/product_uuid disagreeing. The latter was buggy and
this fixes it.
Reported-by: Federico Simoncelli <fsimonce@redhat.com>
Fixes: 9f9c9cbb ("drivers/firmware/dmi_scan.c: fetch dmi version from SMBIOS if it exists")
Fixes: 79bae42d ("dmi_scan: refactor dmi_scan_machine(), {smbios,dmi}_present()")
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Jean Delvare <jdelvare@suse.de>

The dn->name is expected to be used as a literal, so add the missing
"%s".

Fixes: 263b4c1a (ACPI / property: Expose data-only subnodes via sysfs)
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Pull drm nouveau fix from Dave Airlie:
 "Still not back to work, but I decided to forward this fix"

* 'drm-fixes' of git://people.freedesktop.org/~airlied/linux:
  drm/nouveau/gr/nv40: fix oops in interrupt handler

Pull IOMMU fixes from Joerg Roedel:

 - Two build issues, one in the ipmmu-vmsa driver and one for the new
   generic dma-api implemention used on arm64

 - A performance fix for said dma-api implemention

 - An issue caused by a wrong offset in map_sg in the same code as above

* tag 'iommu-fixes-v4.4-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu:
  iommu/dma: Use correct offset in map_sg
  iommu/ipmmu-vmsa: Don't truncate ttbr if LPAE is not enabled
  iommu/dma: Avoid unlikely high-order allocations
  iommu/dma: Add some missing #includes

Pull ftrace fix from Steven Rostedt:
 "PeiyangX Qiu reported that if a module fails to load between calling
  ftrace_module_init() and do_init_module() that the allocations made in
  ftrace_module_init() will not be freed, resulting in a memory leak.

  The solution is to call ftrace_release_mod() on the failing module in
  the fail path befor do_init_module() is called.  This will remove any
  allocations made for that module, and nothing if ftrace_module_init()
  wasn't called yet for that module.

  Note, once do_init_module() is called, the MODULE_GOING notifiers are
  called for the failed module, which calls into the ftrace code to do
  the proper clean up (basically calling ftrace_release_mod())"

* tag 'trace-v4.4-rc4-4' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  ftrace/module: Call clean up function when module init fails early

If the module init code fails after calling ftrace_module_init() and before
calling do_init_module(), we can suffer from a memory leak. This is because
ftrace_module_init() allocates pages to store the locations that ftrace
hooks are placed in the module text. If do_init_module() fails, it still
calls the MODULE_GOING notifiers which will tell ftrace to do a clean up of
the pages it allocated for the module. But if load_module() fails before
then, the pages allocated by ftrace_module_init() will never be freed.

Call ftrace_release_mod() on the module if load_module() fails before
getting to do_init_module().

Link: http://lkml.kernel.org/r/567CEA31.1070507@intel.comReported-by: "Qiu, PeiyangX" <peiyangx.qiu@intel.com>
Fixes: a949ae56 "ftrace/module: Hardcode ftrace_module_init() call into load_module()"
Cc: stable@vger.kernel.org # v2.6.38+
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Since WM8650 has the same 'WMT' SDHC controller as WM8505, and the driver
is already in the kernel, this node enables the controller support for
WM8650
Signed-off-by: Roman Volkov <rvolkov@v1ros.org>
Reviewed-by: Alexey Charkov <alchark@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Commit 69fb4dca ("power: Add an axp20x-usb-power driver") introduced a
new driver for the USB power supply used on various Allwinner based SBCs.
However, the driver was not added to multi_v7_defconfig which breaks USB
support for some boards (e.g. LeMaker BananaPi) as the kernel will now
turn off the USB power supply during boot by default if the driver isn't
present. (This was not the case in linux 4.3 or lower where the USB power
was always left on.)

Hence, add the driver to multi_v7_defconfig in order to keep USB support
working on those boards that require it.
Signed-off-by: Timo Sigurdsson <public_timo.s@silentcreek.de>
Tested-by: Timo Sigurdsson <public_timo.s@silentcreek.de>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

While setting the KVM PIT counters in 'kvm_pit_load_count', if
'hpet_legacy_start' is set, the function disables the timer on
channel[0], instead of the respective index 'channel'. This is
because channels 1-3 are not linked to the HPET.  Fix the caller
to only activate the special HPET processing for channel 0.
Reported-by: P J P <pjp@fedoraproject.org>
Fixes: 0185604cSigned-off-by: Paolo Bonzini <pbonzini@redhat.com>

When mapping a non-page-aligned scatterlist entry, we copy the original
offset to the output DMA address before aligning it to hand off to
iommu_map_sg(), then later adding the IOVA page address portion to get
the final mapped address. However, when the IOVA page size is smaller
than the CPU page size, it is the offset within the IOVA page we want,
not that within the CPU page, which can easily be larger than an IOVA
page and thus result in an incorrect final address.

Fix the bug by taking only the IOVA-aligned part of the offset as the
basis of the DMA address, not the whole thing.
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

single nv40 oops fix.

* 'linux-4.4' of git://github.com/skeggsb/linux:
  drm/nouveau/gr/nv40: fix oops in interrupt handler

For interrupt controller that doesn't support irq_disable and hardware
with level interrupt, an extra interrupt can be pending. This patch fixes
the issue by setting IRQ_DISABLE_UNLAZY flag for the interrupt line.

Reference: http://git.kernel.org/tip/e9849777d0e27cdd2902805be51da73e7c79578cSigned-off-by: Rameshwar Prasad Sahu <rsahu@apm.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

These async_XX functions are called from md/raid5 in an atomic
section, between get_cpu() and put_cpu(), so they must not sleep.
So use GFP_NOWAIT rather than GFP_IO.

Dan Williams writes: Longer term async_tx needs to be merged into md
directly as we can allocate this unmap data statically per-stripe
rather than per request.

Fixed: 7476bd79 ("async_pq: convert to dmaengine_unmap_data")
Cc: stable@vger.kernel.org (v3.13+)
Reported-and-tested-by: Stanislav Samsonov <slava@annapurnalabs.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

Commit 0976c946
"arm/versatile: Fix versatile irq specifications"
has an off-by-one error on the Versatile AB that has
been regressing the Versatile AB hardware for some time.

However it seems like the interrupt assignments have
never been correct and I have now adjusted them according
to the specification. The masks for the valid interrupts
made it impossible to assign the right SIC interrupt
for the MMCI, so I went in and fixed these to correspond
to the specifications, and added references if anyone
wants to double-check.

Due to the Versatile PB including the Versatile AB
as a base DTS file, we need to override and correct
some values to correspond to the actual changes in the
hardware.

For the Versatile PB I don't think the IRQ line
assignment for MMCI has ever been correct for either of
the two MMCI blocks. It would be nice if someone with the
physical PB board could test this.

Patch tested on the Versatile AB, QEMU for Versatile AB
and QEMU for Versatile PB.

Cc: Rob Herring <robh@kernel.org>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: stable@vger.kernel.org
Fixes: 0976c946 ("arm/versatile: Fix versatile irq specifications")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>

The Nomadik has sporadic crashes because of these latencies, setting
them to max makes the platform work nicely, so use this values for
now.

These latencies were set to 2 since the Nomadik platform was merged,
but I suspect they never took effect until the right size and
associativity for the cache was specified in the device tree and
that is why the crash comes now.

Cc: stable@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>

Pull MTD fixes from Brian Norris:
 "Three last MTD fixes for v4.4.  These are all fixes for regressions
  and bugs reported mid cycle.  Unfortunately, some of them took a bit
  long to get proper testing and feedback.

   - Assign the default MTD name earlier in the registration process, so
     partition parsers (like cmdlinepart) see the right name.  Without
     this, some systems may come up with unpartitioned flash.  This was
     a v4.4-rc1 regression.

   - Revert some new Winbond SPI NOR flash unlocking/locking support;
     new code in v4.4 caused regressions on some Spansion flash.

   - Fix mis-typed parameter ordering in SPI NOR unlock function; this
     bug was introduced in v4.4-rc1"

* tag 'for-linus-20160106' of git://git.infradead.org/linux-mtd:
  mtd: spi-nor: fix stm_is_locked_sr() parameters
  mtd: spi-nor: fix Spansion regressions (aliased with Winbond)
  mtd: fix cmdlinepart parser, early naming for auto-filled MTD

Pull networking fixes from David Miller:
 "As usual, there are a couple straggler bug fixes:

   1) qlcnic_alloc_mbx_args() error returns are not checked in qlcnic
      driver.  Fix from Insu Yun.

   2) SKB refcounting bug in connector, from Florian Westphal.

   3) vrf_get_saddr() has to propagate fib_lookup() errors to it's
      callers, from David Ahern.

   4) Fix AF_UNIX splice/bind deadlock, from Rainer Weikusat.

   5) qdisc_rcu_free() fails to free the per-cpu qstats.  Fix from John
      Fastabend.

   6) vmxnet3 driver passes wrong page to dma_map_page(), fix from
     Shrikrishna Khare.

   7) Don't allow zero cwnd in tcp_cwnd_reduction(), from Yuchung Cheng"

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net:
  tcp: fix zero cwnd in tcp_cwnd_reduction
  Driver: Vmxnet3: Fix regression caused by 5738a09d
  net: qmi_wwan: Add WeTelecom-WPD600N
  mkiss: fix scribble on freed memory
  net: possible use after free in dst_release
  net: sched: fix missing free per cpu on qstats
  ARM: net: bpf: fix zero right shift
  6pack: fix free memory scribbles
  net: filter: make JITs zero A for SKF_AD_ALU_XOR_X
  bridge: Only call /sbin/bridge-stp for the initial network namespace
  af_unix: Fix splice-bind deadlock
  net: Propagate lookup failure in l3mdev_get_saddr to caller
  r8152: add reset_resume function
  connector: bump skb->users before callback invocation
  cxgb4: correctly handling failed allocation
  qlcnic: correctly handle qlcnic_alloc_mbx_args

Patch 3759824d ("tcp: PRR uses CRB mode by default and SS mode
conditionally") introduced a bug that cwnd may become 0 when both
inflight and sndcnt are 0 (cwnd = inflight + sndcnt). This may lead
to a div-by-zero if the connection starts another cwnd reduction
phase by setting tp->prior_cwnd to the current cwnd (0) in
tcp_init_cwnd_reduction().

To prevent this we skip PRR operation when nothing is acked or
sacked. Then cwnd must be positive in all cases as long as ssthresh
is positive:

1) The proportional reduction mode
   inflight > ssthresh > 0

2) The reduction bound mode
  a) inflight == ssthresh > 0

  b) inflight < ssthresh
     sndcnt > 0 since newly_acked_sacked > 0 and inflight < ssthresh

Therefore in all cases inflight and sndcnt can not both be 0.
We check invalid tp->prior_cwnd to avoid potential div0 bugs.

In reality this bug is triggered only with a sequence of less common
events.  For example, the connection is terminating an ECN-triggered
cwnd reduction with an inflight 0, then it receives reordered/old
ACKs or DSACKs from prior transmission (which acks nothing). Or the
connection is in fast recovery stage that marks everything lost,
but fails to retransmit due to local issues, then receives data
packets from other end which acks nothing.

Fixes: 3759824d ("tcp: PRR uses CRB mode by default and SS mode conditionally")
Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Reported-by: Bingkuo Liu <bingkuol@vmware.com>
Signed-off-by: Shrikrishna Khare <skhare@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

The WeTelecom-WPD600N is an LTE module that, in addition to supporting most
"normal" bands, also supports LTE over 450MHz. Manual testing showed that
only interface number three replies to QMI messages.

Cc: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Kristian Evensen <kristian.evensen@gmail.com>
Acked-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>