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linux/drivers
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Will Deacon 71c0b9a65c vhost: Remove redundant use of read_barrier_depends() barrier 
Since commit 76ebbe78f7 ("locking/barriers: Add implicit
smp_read_barrier_depends() to READ_ONCE()"), there is no need to use
smp_read_barrier_depends() outside of the Alpha architecture code.

Unfortunately, there is precisely _one_ user in the vhost code, and
there isn't an obvious READ_ONCE() access making the barrier
redundant. However, on closer inspection (thanks, Jason), it appears
that vring synchronisation between the producer and consumer occurs via
the 'avail_idx' field, which is followed up by an rmb() in
vhost_get_vq_desc(), making the read_barrier_depends() redundant on
Alpha.

Jason says:

  | I'm also confused about the barrier here, basically in driver side
  | we did:
  |
  | 1) allocate pages
  | 2) store pages in indirect->addr
  | 3) smp_wmb()
  | 4) increase the avail idx (somehow a tail pointer of vring)
  |
  | in vhost we did:
  |
  | 1) read avail idx
  | 2) smp_rmb()
  | 3) read indirect->addr
  | 4) read from indirect->addr
  |
  | It looks to me even the data dependency barrier is not necessary
  | since we have rmb() which is sufficient for us to the correct
  | indirect->addr and driver are not expected to do any writing to
  | indirect->addr after avail idx is increased

Remove the redundant barrier invocation.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Suggested-by: Jason Wang <jasowang@redhat.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
2020-07-21 10:50:36 +01:00
..
accessibility treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
acpi Merge branch 'acpi-sysfs' 2020-06-26 17:06:29 +02:00
amba ARM: tegra: Replace zero-length array with flexible-array 2020-06-15 23:08:28 -05:00
android binder: fix null deref of proc->context 2020-06-23 07:54:46 +02:00
ata libata-5.8-2020-06-19 2020-06-19 13:09:40 -07:00
atm treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
auxdisplay treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
base Power management fixes for 5.8-rc3 2020-06-26 12:32:11 -07:00
bcma
block block-5.8-2020-06-19 2020-06-19 13:11:26 -07:00
bluetooth Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-06-03 16:27:18 -07:00
bus Fixes for omaps for v5.8 2020-06-28 14:41:55 +02:00
cdrom Merge branch 'work.sysctl' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-06-10 16:05:54 -07:00
char Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-06-21 10:01:03 -07:00
clk clk: sifive: allocate sufficient memory for struct __prci_data 2020-06-25 15:04:13 -07:00
clocksource clocksource/drivers/timer-riscv: Use per-CPU timer interrupt 2020-06-09 19:11:22 -07:00
connector treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
counter
cpufreq cpufreq: intel_pstate: Add one more OOB control bit 2020-06-23 17:24:32 +02:00
cpuidle cpuidle: Rearrange s2idle-specific idle state entry code 2020-06-25 13:52:53 +02:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-06-21 10:01:03 -07:00
dax device-dax: add memory via add_memory_driver_managed() 2020-06-04 19:06:23 -07:00
dca
devfreq
dio maccess: rename probe_kernel_{read,write} to copy_{from,to}_kernel_nofault 2020-06-17 10:57:41 -07:00
dma dmaengine: tegra-apb: Replace zero-length array with flexible-array 2020-06-15 23:08:32 -05:00
dma-buf treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
edac EDAC/amd64: Read back the scrub rate PCI register on F15h 2020-06-18 20:25:25 +02:00
eisa treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
extcon extcon: arizona: Fix runtime PM imbalance on error 2020-05-29 17:36:02 +09:00
firewire firewire: ohci: Replace zero-length array with flexible-array 2020-06-15 23:08:31 -05:00
firmware ARM: SoC fixes for v5.8 2020-06-28 14:55:18 -07:00
fpga FPGA Manager fixes for 5.8-rc1 2020-06-26 17:26:31 +02:00
fsi treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
gnss treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
gpio treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
gpu Short summary of fixes pull (less than what git shortlog provides): 2020-06-26 13:49:17 +10:00
greybus treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
hid treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
hsi treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
hv hyperv-next for 5.8 2020-06-03 15:00:05 -07:00
hwmon Merge branch 'x86/entry' into ras/core 2020-06-11 15:17:57 +02:00
hwspinlock
hwtracing stm class: Replace zero-length array with flexible-array 2020-06-15 23:08:32 -05:00
i2c i2c: core: check returned size of emulated smbus block read 2020-06-26 10:18:35 +02:00
i3c
ide treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
idle
iio treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
infiniband IB/hfi1: Add atomic triggered sleep/wakeup 2020-06-24 16:13:38 -03:00
input maccess: rename probe_kernel_{read,write} to copy_{from,to}_kernel_nofault 2020-06-17 10:57:41 -07:00
interconnect More power management updates for 5.8-rc1 2020-06-10 14:04:39 -07:00
iommu iommu/vt-d: Fix misuse of iommu_domain_identity_map() 2020-06-23 10:08:32 +02:00
ipack treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
irqchip clocksource/drivers/timer-riscv: Use per-CPU timer interrupt 2020-06-09 19:11:22 -07:00
isdn treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
leds LEDs pull request for 5.8-rc1. 2020-06-04 11:03:45 -07:00
lightnvm for-5.8/block-2020-06-01 2020-06-02 15:29:19 -07:00
macintosh treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
mailbox mailbox: qcom: Add ipq6018 apcs compatible 2020-06-10 22:43:57 -05:00
mcb
md - Quite a few DM zoned target fixes and a Zone append fix in DM core. 2020-06-27 08:57:16 -07:00
media media: omap3isp: remove cacheflush.h 2020-06-26 00:27:37 -07:00
memory
memstick
message scsi: mptscsih: Fix read sense data size 2020-06-24 00:23:17 -04:00
mfd mfd: mt6360: Fix register driver NULL pointer by adding driver name 2020-06-16 09:32:43 +01:00
misc habanalabs: increase h/w timer when checking idle 2020-06-24 12:35:23 +03:00
mmc treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
most
mtd This pull request contains a single change for UBI: 2020-06-10 13:24:40 -07:00
mux
net wil6210: account for napi_gro_receive never returning GRO_DROP 2020-06-25 16:16:21 -07:00
nfc treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
ntb NTB: perf: Fix race condition when run with ntb_test 2020-06-05 20:02:09 -04:00
nubus
nvdimm nvdimm/region: always show the 'align' attribute 2020-06-17 14:08:31 -07:00
nvme nvme-multipath: fix bogus request queue reference put 2020-06-24 18:41:20 +02:00
nvmem
of of: of_mdio: Correct loop scanning logic 2020-06-19 13:39:00 -07:00
opp treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
oprofile oprofile: Replace zero-length array with flexible-array 2020-06-15 23:08:32 -05:00
parisc
parport treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
pci Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
pcmcia treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
perf arm64 merge window fixes for -rc1 2020-06-11 12:53:23 -07:00
phy phy: samsung: Replace zero-length array with flexible-array 2020-06-15 23:08:32 -05:00
pinctrl pinctrl: single: fix function name in documentation 2020-06-20 22:41:32 +02:00
platform Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
pnp treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
power power supply and reset changes for the v5.8 series 2020-06-10 11:28:35 -07:00
powercap Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
pps treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
ps3
ptp treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
pwm pwm: Add missing "CONFIG_" prefix 2020-06-04 19:09:28 +02:00
rapidio rapidio: Replace zero-length array with flexible-array 2020-06-15 23:08:32 -05:00
ras
regulator regulator: mt6358: Remove BROKEN dependency 2020-06-17 13:01:19 +01:00
remoteproc remoteproc updates for v5.8 2020-06-08 13:01:08 -07:00
reset Char/Misc driver patches for 5.8-rc1 2020-06-07 10:59:32 -07:00
rpmsg remoteproc updates for v5.8 2020-06-08 13:01:08 -07:00
rtc RTC for 5.8 2020-06-07 16:11:23 -07:00
s390 SCSI fixes on 20200627 2020-06-27 15:20:03 -07:00
sbus treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
scsi scsi: lpfc: Avoid another null dereference in lpfc_sli4_hba_unset() 2020-06-23 23:56:52 -04:00
sfi treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
sh
siox
slimbus
soc ARM: OMAP fixes for v5.8 2020-06-28 14:57:14 -07:00
soundwire
spi spi: Fixes for v5.8 2020-06-22 09:49:59 -07:00
spmi
ssb
staging Staging: rtl8723bs: prevent buffer overflow in update_sta_support_rate() 2020-06-16 21:25:38 +02:00
target Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
tc
tee mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
thermal - Add the hwmon support on the i.MX SC (Anson Huang) 2020-06-12 14:10:21 -07:00
thunderbolt USB/PHY driver updates for 5.8-rc1 2020-06-07 09:42:16 -07:00
tty kdb: Switch to use safer dbg_io_ops over console APIs 2020-06-26 15:40:16 +01:00
uio
usb USB fixes for 5.8-rc3 2020-06-27 13:12:10 -07:00
vdpa vdpa: fix typos in the comments for __vdpa_alloc_device() 2020-06-22 12:34:21 -04:00
vfio vfio/pci: Fix SR-IOV VF handling with MMIO blocking 2020-06-25 11:04:23 -06:00
vhost vhost: Remove redundant use of read_barrier_depends() barrier 2020-07-21 10:50:36 +01:00
video Short summary of fixes pull (less than what git shortlog provides): 2020-06-26 13:49:17 +10:00
virt treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
virtio virtio-mem: add memory via add_memory_driver_managed() 2020-06-22 12:34:21 -04:00
visorbus treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
vlynq
vme treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
w1 w1: Replace zero-length array with flexible-array 2020-06-15 23:08:32 -05:00
watchdog treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
xen The X86 entry, exception and interrupt code rework 2020-06-13 10:05:47 -07:00
zorro treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
Kconfig
Makefile