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Joe Thornber e2e74d617e dm cache: fix race in writethrough implementation 
We have found a race in the optimisation used in the dm cache
writethrough implementation.  Currently, dm core sends the cache target
two bios, one for the origin device and one for the cache device and
these are processed in parallel.  This patch avoids the race by
changing the code back to a simpler (slower) implementation which
processes the two writes in series, one after the other, until we can
develop a complete fix for the problem.

When the cache is in writethrough mode it needs to send WRITE bios to
both the origin and cache devices.

Previously we've been implementing this by having dm core query the
cache target on every write to find out how many copies of the bio it
wants.  The cache will ask for two bios if the block is in the cache,
and one otherwise.

Then main problem with this is it's racey.  At the time this check is
made the bio hasn't yet been submitted and so isn't being taken into
account when quiescing a block for migration (promotion or demotion).
This means a single bio may be submitted when two were needed because
the block has since been promoted to the cache (catastrophic), or two
bios where only one is needed (harmless).

I really don't want to start entering bios into the quiescing system
(deferred_set) in the get_num_write_bios callback.  Instead this patch
simplifies things; only one bio is submitted by the core, this is
first written to the origin and then the cache device in series.
Obviously this will have a latency impact.

deferred_writethrough_bios is introduced to record bios that must be
later issued to the cache device from the worker thread.  This deferred
submission, after the origin bio completes, is required given that we're
in interrupt context (writethrough_endio).

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2013-03-20 17:21:27 +00:00
..
accessibility
acpi Fixes: 2013-03-12 20:25:53 -07:00
amba Merge branch 'for-linus' of git://git.linaro.org/people/rmk/linux-arm 2013-03-03 11:54:39 -08:00
ata ACPI / glue: Drop .find_bridge() callback from struct acpi_bus_type 2013-03-04 14:23:40 +01:00
atm hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
auxdisplay
base ACPI and power management fixes for 3.9-rc2 2013-03-07 14:54:28 -08:00
bcma Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless into for-davem 2013-03-01 13:52:03 -05:00
block Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client 2013-02-28 17:43:09 -08:00
bluetooth Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2013-02-21 17:40:58 -08:00
bus
cdrom
char Simple virtio-rng fix. 2013-03-12 20:28:45 -07:00
clk clk: Tegra: Remove duplicate smp_twd clock 2013-03-04 17:16:37 -08:00
clocksource ImgTec Meta architecture changes for v3.9-rc1 2013-03-03 12:06:09 -08:00
connector proc connector: reject unprivileged listener bumps 2013-02-27 13:08:35 -05:00
cpufreq cpufreq / intel_pstate: Do not load on VM that does not report max P state. 2013-03-06 23:40:11 +01:00
cpuidle arm-soc: soc-specific updates 2013-02-21 15:27:22 -08:00
crypto Merge git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2013-02-25 15:56:15 -08:00
dca dca: convert to idr_alloc() 2013-02-27 19:10:15 -08:00
devfreq
dio
dma Merge branch 'next' of git://git.infradead.org/users/vkoul/slave-dma 2013-03-03 10:20:22 -08:00
edac Merge branch 'linux_next' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-edac 2013-02-28 20:42:33 -08:00
eisa
extcon Char/Misc driver patches for 3.9-rc1 2013-02-21 13:57:13 -08:00
firewire firewire: convert to idr_alloc() 2013-02-27 19:10:15 -08:00
firmware Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-03-09 16:51:13 -08:00
gpio arm-soc fixes for 3.9-rc2 2013-03-12 10:21:38 -07:00
gpu Merge branch 'drm-nouveau-fixes-3.9' of git://anongit.freedesktop.org/git/nouveau/linux-2.6 into drm-next 2013-03-11 13:53:58 +10:00
hid Merge branch 'for-3.9/upstream-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid 2013-03-08 14:42:52 -08:00
hsi hsi: fix kernel-doc warnings 2013-03-01 13:39:00 -08:00
hv Drivers: hv: vmbus: Use the new infrastructure for delivering VMBUS interrupts 2013-02-27 10:15:53 -08:00
hwmon hwmon: (pmbus/ltc2978) Fix temperature reporting 2013-03-14 09:03:51 -07:00
hwspinlock
i2c idr: remove MAX_IDR_MASK and move left MAX_IDR_* into idr.c 2013-02-27 19:10:20 -08:00
ide Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-02-26 20:16:07 -08:00
idle Merge branch 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2013-02-22 19:25:09 -08:00
iio First round of iio fixes post the 3.9 merge window. 2013-03-06 05:48:24 +08:00
infiniband mlx4: remove leftover idr_pre_get() call 2013-03-13 15:21:46 -07:00
input Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2013-03-11 07:49:37 -07:00
iommu iommu, x86: Add DMA remap fault reason 2013-03-06 09:41:51 +01:00
ipack Char/Misc driver patches for 3.9-rc1 2013-02-21 13:57:13 -08:00
irqchip irqchip: fix typo when moving gic_raise_softirq() 2013-03-04 17:15:33 -08:00
isdn drivers/isdn: checkng length to be sure not memory overflow 2013-03-08 00:35:44 -05:00
leds Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/cooloney/linux-leds 2013-02-26 09:29:02 -08:00
lguest All trivial, thanks to the stuff which didn't quite make it time. 2013-02-26 14:49:12 -08:00
macintosh Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc 2013-02-23 17:09:55 -08:00
mailbox mailbox, pl320-ipc: remove __init from probe function 2013-03-04 14:23:11 +01:00
md dm cache: fix race in writethrough implementation 2013-03-20 17:21:27 +00:00
media arm-soc: late OMAP changes 2013-02-28 20:00:40 -08:00
memory
memstick memstick: move the dereference below the NULL test 2013-02-27 19:10:23 -08:00
message
mfd mfd: twl4030-madc: Remove __exit_p annotation 2013-03-15 07:42:22 +01:00
misc fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
mmc Merge branches 'devel-stable', 'fixes' and 'mmci' into for-linus 2013-03-03 00:32:50 +00:00
mtd fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
net rrunner.c: fix possible memory leak in rr_init_one() 2013-03-10 16:42:23 -04:00
nfc Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-next into for-davem 2013-02-18 13:47:13 -05:00
ntb
nubus
of Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2013-02-21 17:40:58 -08:00
oprofile fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
parisc Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-02-26 20:16:07 -08:00
parport Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux 2013-02-21 17:54:03 -08:00
pci ACPI / glue: Add .match() callback to struct acpi_bus_type 2013-03-04 14:23:40 +01:00
pcmcia Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2013-02-21 17:40:58 -08:00
pinctrl arm-soc: device tree conversions 2013-02-21 15:38:49 -08:00
platform Platform: x86: chromeos_laptop : Add basic platform data for atmel devices 2013-03-08 16:03:29 -08:00
pnp ACPI / glue: Add .match() callback to struct acpi_bus_type 2013-03-04 14:23:40 +01:00
power power: convert to idr_alloc() 2013-02-27 19:10:18 -08:00
pps drivers/pps/clients/pps-gpio.c: use devm_kzalloc 2013-02-27 19:10:23 -08:00
ps3
ptp
pwm pwm: Changes for v3.9-rc1 2013-02-26 09:34:29 -08:00
rapidio
regulator Merge remote-tracking branch 'regulator/fix/twl' into tmp 2013-03-05 10:12:43 +08:00
remoteproc remoteproc: convert to idr_alloc() 2013-02-27 19:10:18 -08:00
rpmsg rpmsg: convert to idr_alloc() 2013-02-27 19:10:18 -08:00
rtc rtc: rtc-mv: Add support for clk to avoid lockups 2013-03-08 21:34:41 +00:00
s390 qdio: remove unused parameters 2013-02-28 09:37:12 +01:00
sbus Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-02-26 20:16:07 -08:00
scsi ACPI / glue: Add .match() callback to struct acpi_bus_type 2013-03-04 14:23:40 +01:00
sfi
sh
sn
spi arm-soc: soc-specific updates 2013-02-21 15:27:22 -08:00
ssb Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux into mips-for-linux-next 2013-02-22 10:07:30 +01:00
staging Merge branch 'akpm' (fixes from Andrew) 2013-03-13 15:21:57 -07:00
target Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending 2013-03-02 11:43:27 -08:00
tc
thermal Fix mis-merge of intel_powerclamp.c resulting in compile error 2013-02-28 20:23:09 -08:00
tty TTY/Serial fixes for 3.9-rc2 2013-03-13 15:02:02 -07:00
uio uio: convert to idr_alloc() 2013-02-27 19:10:19 -08:00
usb USB fixes for 3.9-rc2 2013-03-13 15:03:48 -07:00
uwb
vfio vfio: convert to idr_alloc() 2013-02-27 19:10:19 -08:00
vhost Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending 2013-02-26 11:42:23 -08:00
video ARM: OMAP1: Fix build related to kgdb.h no longer including serial_8250.h 2013-03-04 11:12:16 -08:00
virt
virtio All trivial, thanks to the stuff which didn't quite make it time. 2013-02-26 14:49:12 -08:00
vlynq
vme vme: add missing put_device() after device_register() fails 2013-02-14 09:24:14 -08:00
w1 w1: fix oops when w1_search is called from netlink connector 2013-03-12 16:20:46 -07:00
watchdog watchdog: sp805_wdt depends on ARM 2013-03-01 12:56:26 +01:00
xen Fixes: 2013-03-12 20:25:53 -07:00
zorro new helper: file_inode(file) 2013-02-22 23:31:31 -05:00
Kconfig Char/Misc driver patches for 3.9-rc1 2013-02-21 13:57:13 -08:00
Makefile Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc 2013-02-23 17:09:55 -08:00