That got messed up while porting it from Radeon.
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Ben Skeggs wrote:
A couple of regression fixes, some more boards whitelisted for a hw bug
workaround, gr/ucode fixes for hangs a user is seeing.

The changes look larger than they actually are due to the ucode binaries
(*.fucN.h) being regenerated.

* 'linux-4.4' of git://anongit.freedesktop.org/git/nouveau/linux-2.6:
  drm/nouveau/volt/pwm/gk104: fix an off-by-one resulting in the voltage not being set
  drm/nouveau/nvif: allow userspace access to its own client object
  drm/nouveau/gr/gf100-: fix oops when calling zbc methods
  drm/nouveau/gr/gf117-: assume no PPC if NV_PGRAPH_GPC_GPM_PD_PES_TPC_ID_MASK is zero
  drm/nouveau/gr/gf117-: read NV_PGRAPH_GPC_GPM_PD_PES_TPC_ID_MASK from correct GPC
  drm/nouveau/gr/gf100-: split out per-gpc address calculation macro
  drm/nouveau/bios: return actual size of the buffer retrieved via _ROM
  drm/nouveau/instmem: protect instobj list with a spinlock
  drm/nouveau/pci: enable c800 magic for some unknown Samsung laptop
  drm/nouveau/pci: enable c800 magic for Clevo P157SM

Radeon and amdgpu fixes for 4.4:
- DPM fixes for r7xx devices
- VCE fixes for Stoney
- GPUVM fixes
- Scheduler fixes

* 'drm-fixes-4.4' of git://people.freedesktop.org/~agd5f/linux:
  drm/radeon: make some dpm errors debug only
  drm/radeon: make rv770_set_sw_state failures non-fatal
  drm/amdgpu: move dependency handling out of atomic section v2
  drm/amdgpu: optimize scheduler fence handling
  drm/amdgpu: remove vm->mutex
  drm/amdgpu: add mutex for ba_va->valids/invalids
  drm/amdgpu: adapt vce session create interface changes
  drm/amdgpu: vce use multiple cache surface starting from stoney
  drm/amdgpu: reset vce trap interrupt flag

Pull vfs fixes from Al Viro:
 "A couple of fixes for sendfile lockups caught by Dmitry + a fix for
  ancient sysvfs symlink breakage"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  vfs: Avoid softlockups with sendfile(2)
  vfs: Make sendfile(2) killable even better
  fix sysvfs symlinks

Pull more block layer fixes from Jens Axboe:
 "I wasn't going to send off a new pull before next week, but the blk
  flush fix from Jan from the other day introduced a regression.  It's
  rare enough not to have hit during testing, since it requires both a
  device that rejects the first flush, and bad timing while it does
  that.  But since someone did hit it, let's get the revert into 4.4-rc3
  so we don't have a released rc with that known issue.

  Apart from that revert, three other fixes:

   - From Christoph, a fix for a missing unmap in NVMe request
     preparation.

   - An NVMe fix from Nishanth that fixes data corruption on powerpc.

   - Also from Christoph, fix a list_del() attempt on blk-mq that didn't
     have a matching list_add() at timer start"

* 'for-linus' of git://git.kernel.dk/linux-block:
  Revert "blk-flush: Queue through IO scheduler when flush not required"
  block: fix blk_abort_request for blk-mq drivers
  nvme: add missing unmaps in nvme_queue_rq
  NVMe: default to 4k device page size

This reverts commit 1b2ff19e.

Jan writes:

--

Thanks for report! After some investigation I found out we allocate
elevator specific data in __get_request() only for non-flush requests. And
this is actually required since the flush machinery uses the space in
struct request for something else. Doh. So my patch is just wrong and not
easy to fix since at the time __get_request() is called we are not sure
whether the flush machinery will be used in the end. Jens, please revert
1b2ff19e. Thanks!

I'm somewhat surprised that you can reliably hit the race where flushing
gets disabled for the device just while the request is in flight. But I
guess during boot it makes some sense.

--

So let's just revert it, we can fix the queue run manually after the
fact. This race is rare enough that it didn't trigger in testing, it
requires the specific disable-while-in-flight scenario to trigger.

Pull KVM fixes from Paolo Bonzini:
 "Bug fixes for all architectures.  Nothing really stands out"

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (21 commits)
  KVM: nVMX: remove incorrect vpid check in nested invvpid emulation
  arm64: kvm: report original PAR_EL1 upon panic
  arm64: kvm: avoid %p in __kvm_hyp_panic
  KVM: arm/arm64: vgic: Trust the LR state for HW IRQs
  KVM: arm/arm64: arch_timer: Preserve physical dist. active state on LR.active
  KVM: arm/arm64: Fix preemptible timer active state crazyness
  arm64: KVM: Add workaround for Cortex-A57 erratum 834220
  arm64: KVM: Fix AArch32 to AArch64 register mapping
  ARM/arm64: KVM: test properly for a PTE's uncachedness
  KVM: s390: fix wrong lookup of VCPUs by array index
  KVM: s390: avoid memory overwrites on emergency signal injection
  KVM: Provide function for VCPU lookup by id
  KVM: s390: fix pfmf intercept handler
  KVM: s390: enable SIMD only when no VCPUs were created
  KVM: x86: request interrupt window when IRQ chip is split
  KVM: x86: set KVM_REQ_EVENT on local interrupt request from user space
  KVM: x86: split kvm_vcpu_ready_for_interrupt_injection out of dm_request_for_irq_injection
  KVM: x86: fix interrupt window handling in split IRQ chip case
  MIPS: KVM: Uninit VCPU in vcpu_create error path
  MIPS: KVM: Fix CACHE immediate offset sign extension
  ...

"Could not force DPM to low", etc. is usually harmless and
just confuses users.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

This patch removes the vpid check when emulating nested invvpid
instruction of type all-contexts invalidation. The existing code is
incorrect because:
 (1) According to Intel SDM Vol 3, Section "INVVPID - Invalidate
     Translations Based on VPID", invvpid instruction does not check
     vpid in the invvpid descriptor when its type is all-contexts
     invalidation.
 (2) According to the same document, invvpid of type all-contexts
     invalidation does not require there is an active VMCS, so/and
     get_vmcs12() in the existing code may result in a NULL-pointer
     dereference. In practice, it can crash both KVM itself and L1
     hypervisors that use invvpid (e.g. Xen).
Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reported-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Martin Peres <martin.peres@free.fr>

Regression from "abi16: implement limited interoperability with
usif/nvif".
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

Somehow missed these two when removing dodgy void casts during the
rework.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

fdo#92761
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

Each GPCCS unit was reading the mask from GPC0, which causes problems on
boards where some GPCs are missing PPCs.

Part of the fix for fdo#92761.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

There's a few places where we need to access a GPC register from ucode,
but outside of the falcon's io address space.  To do this we need to
calculate the offset based on which GPC we're executing on.

This used to be done manually, but we've since found a "base" offset
that can be added by the hardware.  To use this, an extra bit needs to
be set in the register address, which is what this macro achieves.

There should be no functional change from this commit.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

Fixes detection of a failed attempt at fetching the entire ROM image
in one-shot (a violation of the spec, that works a lot of the time).

Tested on a HP Zbook 15 G2.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

No locking is required for the traversal of this list, as it only
happens during suspend/resume where nothing else can be executing.

Fixes some of the issues noticed during parallel piglit runs.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

fdo#70354 - comment #88.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

this is needed for my gpu
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

We only added the request to the request list for the !blk-mq case,
so we should only delete it in that case as well.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

When we fail various metadata related operations in nvme_queue_rq we
need to unmap the data SGL.

Cc: stable@vger.kernel.org
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

We received a bug report recently when DDW (64-bit direct DMA on Power)
is not enabled for NVMe devices. In that case, we fall back to 32-bit
DMA via the IOMMU, which is always done via 4K TCEs (Translation Control
Entries).

The NVMe device driver, though, assumes that the DMA alignment for the
PRP entries will match the device's page size, and that the DMA aligment
matches the kernel's page aligment. On Power, the the IOMMU page size,
as mentioned above, can be 4K, while the device can have a page size of
8K, while the kernel has a page size of 64K. This eventually trips the
BUG_ON in nvme_setup_prps(), as we have a 'dma_len' that is a multiple
of 4K but not 8K (e.g., 0xF000).

In this particular case of page sizes, we clearly want to use the
IOMMU's page size in the driver. And generally, the NVMe driver in this
function should be using the IOMMU's page size for the default device
page size, rather than the kernel's page size. There is not currently an
API to obtain the IOMMU's page size across all architectures and in the
interest of a stop-gap fix to this functional issue, default the NVMe
device page size to 4K, with the intent of adding such an API and
implementation across all architectures in the next merge window.

With the functionally equivalent v3 of this patch, our hardware test
exerciser survives when using 32-bit DMA; without the patch, the kernel
will BUG within a few minutes.

Signed-off-by: Nishanth Aravamudan <nacc at linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

Pull device mapper fixes from Mike Snitzer:
 "Two fixes for 4.4-rc1's DM ioctl changes that introduced the potential
  for infinite recursion on ioctl (with DM multipath).

  And four stable fixes:

   - A DM thin-provisioning fix to restore 'error_if_no_space' setting
     when a thin-pool is made writable again (after having been out of
     space).

   - A DM thin-provisioning fix to properly advertise discard support
     for thin volumes that are stacked on a thin-pool whose underlying
     data device doesn't support discards.

   - A DM ioctl fix to allow ctrl-c to break out of an ioctl retry loop
     when DM multipath is configured to 'queue_if_no_path'.

   - A DM crypt fix for a possible hang on dm-crypt device removal"

* tag 'dm-4.4-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
  dm thin: fix regression in advertised discard limits
  dm crypt: fix a possible hang due to race condition on exit
  dm mpath: fix infinite recursion in ioctl when no paths and !queue_if_no_path
  dm: do not reuse dm_blk_ioctl block_device input as local variable
  dm: fix ioctl retry termination with signal
  dm thin: restore requested 'error_if_no_space' setting on OODS to WRITE transition

I got a crash during a "perf top" session that was caused by a race in
__task_pid_nr_ns() :

pid_nr_ns() was inlined, but apparently compiler chose to read
task->pids[type].pid twice, and the pid->level dereference crashed
because we got a NULL pointer at the second read :

    if (pid && ns->level <= pid->level) { // CRASH

Just use RCU API properly to solve this race, and not worry about "perf
top" crashing hosts :(

get_task_pid() can benefit from same fix.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Merge tag 'kvm-arm-for-v4.4-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into kvm-master

KVM/ARM Fixes for v4.4-rc3.

Includes some timer fixes, properly unmapping PTEs, an errata fix, and two
tweaks to the EL2 panic code.

Pull block layer fixes from Jens Axboe:
 "A round of fixes/updates for the current series.

  This looks a little bigger than it is, but that's mainly because we
  pushed the lightnvm enabled null_blk change out of the merge window so
  it could be updated a bit.  The rest of the volume is also mostly
  lightnvm.  In particular:

   - Lightnvm.  Various fixes, additions, updates from Matias and
     Javier, as well as from Wenwei Tao.

   - NVMe:
        - Fix for potential arithmetic overflow from Keith.
        - Also from Keith, ensure that we reap pending completions from
          a completion queue before deleting it.  Fixes kernel crashes
          when resetting a device with IO pending.
        - Various little lightnvm related tweaks from Matias.

   - Fixup flushes to go through the IO scheduler, for the cases where a
     flush is not required.  Fixes a case in CFQ where we would be
     idling and not see this request, hence not break the idling.  From
     Jan Kara.

   - Use list_{first,prev,next} in elevator.c for cleaner code.  From
     Gelian Tang.

   - Fix for a warning trigger on btrfs and raid on single queue blk-mq
     devices, where we would flush plug callbacks with preemption
     disabled.  From me.

   - A mac partition validation fix from Kees Cook.

   - Two merge fixes from Ming, marked stable.  A third part is adding a
     new warning so we'll notice this quicker in the future, if we screw
     up the accounting.

   - Cleanup of thread name/creation in mtip32xx from Rasmus Villemoes"

* 'for-linus' of git://git.kernel.dk/linux-block: (32 commits)
  blk-merge: warn if figured out segment number is bigger than nr_phys_segments
  blk-merge: fix blk_bio_segment_split
  block: fix segment split
  blk-mq: fix calling unplug callbacks with preempt disabled
  mac: validate mac_partition is within sector
  mtip32xx: use formatting capability of kthread_create_on_node
  NVMe: reap completion entries when deleting queue
  lightnvm: add free and bad lun info to show luns
  lightnvm: keep track of block counts
  nvme: lightnvm: use admin queues for admin cmds
  lightnvm: missing free on init error
  lightnvm: wrong return value and redundant free
  null_blk: do not del gendisk with lightnvm
  null_blk: use device addressing mode
  null_blk: use ppa_cache pool
  NVMe: Fix possible arithmetic overflow for max segments
  blk-flush: Queue through IO scheduler when flush not required
  null_blk: register as a LightNVM device
  elevator: use list_{first,prev,next}_entry
  lightnvm: cleanup queue before target removal
  ...

On some cards it takes a relatively long time for the change
to take place.  Make a timeout non-fatal.

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=76130Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

If we call __kvm_hyp_panic while a guest context is active, we call
__restore_sysregs before acquiring the system register values for the
panic, in the process throwing away the PAR_EL1 value at the point of
the panic.

This patch modifies __kvm_hyp_panic to stash the PAR_EL1 value prior to
restoring host register values, enabling us to report the original
values at the point of the panic.
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

Currently __kvm_hyp_panic uses %p for values which are not pointers,
such as the ESR value. This can confusingly lead to "(null)" being
printed for the value.

Use %x instead, and only use %p for host pointers.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

We were probing the physial distributor state for the active state of a
HW virtual IRQ, because we had seen evidence that the LR state was not
cleared when the guest deactivated a virtual interrupted.

However, this issue turned out to be a software bug in the GIC, which
was solved by: 84aab5e68c2a5e1e18d81ae8308c3ce25d501b29
(KVM: arm/arm64: arch_timer: Preserve physical dist. active
state on LR.active, 2015-11-24)

Therefore, get rid of the complexities and just look at the LR.
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

We were incorrectly removing the active state from the physical
distributor on the timer interrupt when the timer output level was
deasserted.  We shouldn't be doing this without considering the virtual
interrupt's active state, because the architecture requires that when an
LR has the HW bit set and the pending or active bits set, then the
physical interrupt must also have the corresponding bits set.

This addresses an issue where we have been observing an inconsistency
between the LR state and the physical distributor state where the LR
state was active and the physical distributor was not active, which
shouldn't happen.
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

We were setting the physical active state on the GIC distributor in a
preemptible section, which could cause us to set the active state on
different physical CPU from the one we were actually going to run on,
hacoc ensues.

Since we are no longer descheduling/scheduling soft timers in the
flush/sync timer functions, simply moving the timer flush into a
non-preemptible section.
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

Cortex-A57 parts up to r1p2 can misreport Stage 2 translation faults
when a Stage 1 permission fault or device alignment fault should
have been reported.

This patch implements the workaround (which is to validate that the
Stage-1 translation actually succeeds) by using code patching.

Cc: stable@vger.kernel.org
Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

When running a 32bit guest under a 64bit hypervisor, the ARMv8
architecture defines a mapping of the 32bit registers in the 64bit
space. This includes banked registers that are being demultiplexed
over the 64bit ones.

On exceptions caused by an operation involving a 32bit register, the
HW exposes the register number in the ESR_EL2 register. It was so
far understood that SW had to distinguish between AArch32 and AArch64
accesses (based on the current AArch32 mode and register number).

It turns out that I misinterpreted the ARM ARM, and the clue is in
D1.20.1: "For some exceptions, the exception syndrome given in the
ESR_ELx identifies one or more register numbers from the issued
instruction that generated the exception. Where the exception is
taken from an Exception level using AArch32 these register numbers
give the AArch64 view of the register."

Which means that the HW is already giving us the translated version,
and that we shouldn't try to interpret it at all (for example, doing
an MMIO operation from the IRQ mode using the LR register leads to
very unexpected behaviours).

The fix is thus not to perform a call to vcpu_reg32() at all from
vcpu_reg(), and use whatever register number is supplied directly.
The only case we need to find out about the mapping is when we
actively generate a register access, which only occurs when injecting
a fault in a guest.

Cc: stable@vger.kernel.org
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

The open coded tests for checking whether a PTE maps a page as
uncached use a flawed '(pte_val(xxx) & CONST) != CONST' pattern,
which is not guaranteed to work since the type of a mapping is
not a set of mutually exclusive bits

For HYP mappings, the type is an index into the MAIR table (i.e, the
index itself does not contain any information whatsoever about the
type of the mapping), and for stage-2 mappings it is a bit field where
normal memory and device types are defined as follows:

    #define MT_S2_NORMAL            0xf
    #define MT_S2_DEVICE_nGnRE      0x1

I.e., masking *and* comparing with the latter matches on the former,
and we have been getting lucky merely because the S2 device mappings
also have the PTE_UXN bit set, or we would misidentify memory mappings
as device mappings.

Since the unmap_range() code path (which contains one instance of the
flawed test) is used both for HYP mappings and stage-2 mappings, and
considering the difference between the two, it is non-trivial to fix
this by rewriting the tests in place, as it would involve passing
down the type of mapping through all the functions.

However, since HYP mappings and stage-2 mappings both deal with host
physical addresses, we can simply check whether the mapping is backed
by memory that is managed by the host kernel, and only perform the
D-cache maintenance if this is the case.

Cc: stable@vger.kernel.org
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Pavel Fedin <p.fedin@samsung.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

We had seen lots of reports of this kind issue, so add one
warnning in blk-merge, then it can be triggered easily and
avoid to depend on warning/bug from drivers.
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

Commit bdced438(block: setup bi_phys_segments after
splitting) introduces function of computing bio->bi_phys_segments
during bio splitting.

Unfortunately both bio->bi_seg_front_size and bio->bi_seg_back_size
arn't computed, so too many physical segments may be obtained
for one request since both the two are used to check if one segment
across two bios can be possible.

This patch fixes the issue by computing the two variables in
blk_bio_segment_split().

Fixes: bdced438(block: setup bi_phys_segments after splitting)
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Reported-by: Mark Salter <msalter@redhat.com>
Tested-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Tested-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

Inside blk_bio_segment_split(), previous bvec pointer(bvprvp)
always points to the iterator local variable, which is obviously
wrong, so fix it by pointing to the local variable of 'bvprv'.

Fixes: 5014c311(block: fix bogus compiler warnings in blk-merge.c)
Cc: stable@kernel.org #4.3
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Reported-by: Mark Salter <msalter@redhat.com>
Tested-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Tested-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

The following test program from Dmitry can cause softlockups or RCU
stalls as it copies 1GB from tmpfs into eventfd and we don't have any
scheduling point at that path in sendfile(2) implementation:

        int r1 = eventfd(0, 0);
        int r2 = memfd_create("", 0);
        unsigned long n = 1<<30;
        fallocate(r2, 0, 0, n);
        sendfile(r1, r2, 0, n);

Add cond_resched() into __splice_from_pipe() to fix the problem.

CC: Dmitry Vyukov <dvyukov@google.com>
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Commit 296291cd (mm: make sendfile(2) killable) fixed an issue where
sendfile(2) was doing a lot of tiny writes into a filesystem and thus
was unkillable for a long time. However sendfile(2) can be (mis)used to
issue lots of writes into arbitrary file descriptor such as evenfd or
similar special file descriptors which never hit the standard filesystem
write path and thus are still unkillable. E.g. the following example
from Dmitry burns CPU for ~16s on my test system without possibility to
be killed:

        int r1 = eventfd(0, 0);
        int r2 = memfd_create("", 0);
        unsigned long n = 1<<30;
        fallocate(r2, 0, 0, n);
        sendfile(r1, r2, 0, n);

There are actually quite a few tests for pending signals in sendfile
code however we data to write is always available none of them seems to
trigger. So fix the problem by adding a test for pending signal into
splice_from_pipe_next() also before the loop waiting for pipe buffers to
be available. This should fix all the lockup issues with sendfile of the
do-ton-of-tiny-writes nature.

CC: stable@vger.kernel.org
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>