Commit 7667aa0630 added logic to wait for
the last queue of the group to become busy (have at least one request),
so that the group does not lose out for not being continuously
backlogged. The commit did not check for the condition that the last
queue already has some requests. As a result, if the queue already has
requests, wait_busy is set. Later on, cfq_select_queue() checks the
flag, and decides that since the queue has a request now and wait_busy
is set, the queue is expired. This results in early expiration of the
queue.
This patch fixes the problem by adding a check to see if queue already
has requests. If it does, wait_busy is not set. As a result, time slices
do not expire early.
The queues with more than one request are usually buffered writers.
Testing shows improvement in isolation between buffered writers.
Cc: stable@kernel.org
Signed-off-by: Justin TerAvest <teravest@google.com>
Reviewed-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
o Jeff Moyer was doing some testing on a RAM backed disk and
blkiocg_lookup_group() showed up high overhead after memcpy(). Similarly
somebody else reported that blkiocg_lookup_group() is eating 6% extra
cpu. Though looking at the code I can't think why the overhead of
this function is so high. One thing is that it is called with very high
frequency (once for every IO).
o For lot of folks blkio controller will be compiled in but they might
not have actually created cgroups. Hence optimize the case of root
cgroup where we can avoid calling blkiocg_lookup_group() if IO is happening
in root group (common case).
Reported-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
o Rename a function to give it more approprate name. We are calculating
cfq queue slice and function name gives the impression as if cfq group
slice length is being calculated.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Change Makefile to use <modules>-y instead of <modules>-objs because -objs
is deprecated and should now be switched. According to
(documentation/kbuild/makefiles.txt).
Signed-off-by: Tracey Dent <tdent48227@gmail.com>
Cc: "Ed L. Cashin" <ecashin@coraid.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Performing
$ sudo mount -o loop -o umask=0 /dev/sdb1 /mnt/
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so
$ sudo modprobe -r loop
results in oops:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
IP: [<ffffffff812479d4>] do_raw_spin_lock+0x14/0x122
Process modprobe (pid: 6189, threadinfo ffff88009a898000, task ffff880154a88000)
Call Trace:
[<ffffffff81486788>] _raw_spin_lock_irq+0x4a/0x51
[<ffffffff8123404b>] ? blk_throtl_exit+0x3b/0xa0
[<ffffffff8105b120>] ? cancel_delayed_work_sync+0xd/0xf
[<ffffffff8123404b>] blk_throtl_exit+0x3b/0xa0
[<ffffffff81229bc8>] blk_release_queue+0x21/0x65
[<ffffffff8123bb06>] kobject_release+0x51/0x66
[<ffffffff8123bab5>] ? kobject_release+0x0/0x66
[<ffffffff8123ce1e>] kref_put+0x43/0x4d
[<ffffffff8123ba27>] kobject_put+0x47/0x4b
[<ffffffff8122717c>] blk_cleanup_queue+0x56/0x5b
[<ffffffffa01c3824>] loop_exit+0x68/0x844 [loop]
[<ffffffff8107cccc>] sys_delete_module+0x1e8/0x25b
[<ffffffff814864c9>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[<ffffffff81002112>] system_call_fastpath+0x16/0x1b
because of an attempt to acquire NULL queue_lock.
I added the same lines as in blk_queue_make_request -
index 44e18c0..49e6a54 100644`fall back to embedded per-queue lock'.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Change Makefile to use <modules>-y instead of <modules>-objs because -objs
is deprecated and should now be switched. According to
(documentation/kbuild/makefiles.txt).
Signed-off-by: Tracey Dent <tdent48227@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Now if we enable blktrace, cfq has too many messages output to the
trace buffer. It is fine if we don't specify any action mask.
But if I do like this:
blktrace /dev/sdb -a issue -a complete -o - | blkparse -i -
I only want to see 'D' and 'C', while with the following command
dd if=/mnt/ocfs2/test of=/dev/null bs=4k count=1 iflag=direct
I will get(with a 2.6.37 vanilla kernel):
8,16 0 0 0.000000000 0 m N cfq3805 alloced
8,16 0 0 0.000004126 0 m N cfq3805 insert_request
8,16 0 0 0.000004884 0 m N cfq3805 add_to_rr
8,16 0 0 0.000008417 0 m N cfq workload slice:300
8,16 0 0 0.000009557 0 m N cfq3805 set_active wl_prio:0 wl_type:2
8,16 0 0 0.000010640 0 m N cfq3805 fifo= (null)
8,16 0 0 0.000011193 0 m N cfq3805 dispatch_insert
8,16 0 0 0.000012221 0 m N cfq3805 dispatched a request
8,16 0 0 0.000012802 0 m N cfq3805 activate rq, drv=1
8,16 0 1 0.000013181 3805 D R 114759 + 8 [dd]
8,16 0 2 0.000164244 0 C R 114759 + 8 [0]
8,16 0 0 0.000167997 0 m N cfq3805 complete rqnoidle 0
8,16 0 0 0.000168782 0 m N cfq3805 set_slice=100
8,16 0 0 0.000169874 0 m N cfq3805 arm_idle: 8 group_idle: 0
8,16 0 0 0.000170189 0 m N cfq schedule dispatch
8,16 0 0 0.000397938 0 m N cfq3805 slice expired t=0
8,16 0 0 0.000399763 0 m N cfq3805 sl_used=1 disp=1 charge=1 iops=0 sect=8
8,16 0 0 0.000400227 0 m N cfq3805 del_from_rr
8,16 0 0 0.000400882 0 m N cfq3805 put_queue
See, there are 19 lines while I only need 2. I don't think it is
appropriate for a user.
So this patch will disable any messages if the BLK_TC_NOTIFY isn't set.
Now the output for the same command will look like:
8,16 0 1 0.000000000 4908 D R 114759 + 8 [dd]
8,16 0 2 0.000146827 0 C R 114759 + 8 [0]
Yes, it is what I want to see.
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
* 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
perf: Validate cpu early in perf_event_alloc()
perf: Find_get_context: fix the per-cpu-counter check
perf: Fix contexted inheritance
* 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
x86: Clear irqstack thread_info
x86: Make relocatable kernel work with new binutils
* 'upstream' of git://git.linux-mips.org/pub/scm/upstream-linus: (26 commits)
MIPS: Malta: enable Cirrus FB console
MIPS: add CONFIG_VIRTUALIZATION for virtio support
MIPS: Implement __read_mostly
MIPS: ath79: add common WMAC device for AR913X based boards
MIPS: ath79: Add initial support for the Atheros AP81 reference board
MIPS: ath79: add common SPI controller device
SPI: Add SPI controller driver for the Atheros AR71XX/AR724X/AR913X SoCs
MIPS: ath79: add common GPIO buttons device
MIPS: ath79: add common watchdog device
MIPS: ath79: add common GPIO LEDs device
MIPS: ath79: add initial support for the Atheros PB44 reference board
MIPS: ath79: utilize the MIPS multi-machine support
MIPS: ath79: add GPIOLIB support
MIPS: Add initial support for the Atheros AR71XX/AR724X/AR931X SoCs
MIPS: jump label: Add MIPS support.
MIPS: Use WARN() in uasm for better diagnostics.
MIPS: Optimize TLB handlers for Octeon CPUs
MIPS: Add LDX and LWX instructions to uasm.
MIPS: Use BBIT instructions in TLB handlers
MIPS: Declare uasm bbit0 and bbit1 functions.
...
This patch adds basic support for LM94 to the LM93 driver. LM94 specific
sensors and features are not supported.
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Acked-by: Jean Delvare <khali@linux-fr.org>
Starting from perf_event_alloc()->perf_init_event(), the kernel
assumes that event->cpu is either -1 or the valid CPU number.
Change perf_event_alloc() to validate this argument early. This
also means we can remove the similar check in
find_get_context().
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: gregkh@suse.de
Cc: stable@kernel.org
LKML-Reference: <20110118161032.GC693@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
If task == NULL, find_get_context() should always check that cpu
is correct.
Afaics, the bug was introduced by 38a81da2 "perf events: Clean
up pid passing", but even before that commit "&& cpu != -1" was
not exactly right, -ESRCH from find_task_by_vpid() is not
accurate.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: gregkh@suse.de
Cc: stable@kernel.org
LKML-Reference: <20110118161008.GB693@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
While most users of a physical Malta board are using the serial port
as the console, a lot of QEMU users would prefer to interact with a
graphical console. Enable the Cirrus FB support in the Malta default
configuration to make that possible. Note that the default console will
still be the serial port, users have to pass "console=tty0" to the
kernel to use the Cirrus FB.
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2001/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Add CONFIG_VIRTUALIZATION to the MIPS architecture and include the
the virtio code there. Used to enable the virtio drivers under QEMU.
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2002/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Just do what everyone else is doing by placing __read_mostly things in
the .data.read_mostly section.
mips_io_port_base can not be read-only (const) and writable
(__read_mostly) at the same time. One of them has to go, so I chose
to eliminate the __read_mostly. It will still get stuck in a portion
of memory that is not adjacent to things that are written, and thus
not be on a dirty cache line, for whatever that is worth.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/1702/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Add common platform_device and helper code to make the registration
of the built-in wireless MAC easier on the Atheros AR9130/AR9132
based boards. Also register the WMAC device on the AR81 board.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: Imre Kaloz <kaloz@openwrt.org>,
Cc: Luis R. Rodriguez <lrodriguez@atheros.com>
Cc: Cliff Holden <Cliff.Holden@Atheros.com>
Cc: Kathy Giori <Kathy.Giori@Atheros.com>
Patchwork: https://patchwork.linux-mips.org/patch/1962/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Several boards are using the built-in SPI controller of the
AR71XX/AR724X/AR913X SoCs. This patch adds common platform_device
and helper code to register it. Additionally, the patch registers
the SPI bus on the PB44 board.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: Imre Kaloz <kaloz@openwrt.org>
Cc: Luis R. Rodriguez <lrodriguez@atheros.com>
Cc: Cliff Holden <Cliff.Holden@Atheros.com>
Cc: Kathy Giori <Kathy.Giori@Atheros.com>
Patchwork: https://patchwork.linux-mips.org/patch/1956/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
The Atheros AR71XX/AR724X/AR913X SoCs have a built-in SPI controller. This
patch implements a driver for that.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: spi-devel-general@lists.sourceforge.net
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Cc: linux-mips@linux-mips.org
Cc: Imre Kaloz <kaloz@openwrt.org>
Cc: Luis R. Rodriguez <lrodriguez@atheros.com>
Cc: Cliff Holden <Cliff.Holden@Atheros.com>
Cc: Kathy Giori <Kathy.Giori@Atheros.com>
Patchwork: https://patchwork.linux-mips.org/patch/1960/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Almost all boards have one or more push buttons connected to GPIO lines.
This patch adds common code to register a platform_device for them.
The patch also adds support for the buttons on the PB44 board.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Imre Kaloz <kaloz@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: Luis R. Rodriguez <lrodriguez@atheros.com>
Cc: Cliff Holden <Cliff.Holden@Atheros.com>
Cc: Kathy Giori <Kathy.Giori@Atheros.com>
Patchwork: https://patchwork.linux-mips.org/patch/1954/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
All supported SoCs have a built-in hardware watchdog driver. This patch
registers a platform_device for that to make it usable.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Imre Kaloz <kaloz@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: Luis R. Rodriguez <lrodriguez@atheros.com>
Cc: Cliff Holden <Cliff.Holden@Atheros.com>
Cc: Kathy Giori <Kathy.Giori@Atheros.com>
Patchwork: https://patchwork.linux-mips.org/patch/1955/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Almost all boards have one or more LEDs connected to GPIO lines. This
patch adds common code to register a platform_device for them.
The patch also adds support for the LEDs on the PB44 board.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Imre Kaloz <kaloz@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: Luis R. Rodriguez <lrodriguez@atheros.com>
Cc: Cliff Holden <Cliff.Holden@Atheros.com>
Cc: Kathy Giori <Kathy.Giori@Atheros.com>
Patchwork: https://patchwork.linux-mips.org/patch/1953/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This patch adds initial support for various Atheros SoCs based on the
MIPS 24Kc core. The following models are supported at the moment:
- AR7130
- AR7141
- AR7161
- AR9130
- AR9132
- AR7240
- AR7241
- AR7242
The current patch contains minimal support only, but the resulting
kernel can boot into user-space with using of an initramfs image on
various boards which are using these SoCs. Support for more built-in
devices and individual boards will be implemented in further patches.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Imre Kaloz <kaloz@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: Luis R. Rodriguez <lrodriguez@atheros.com>
Cc: Cliff Holden <Cliff.Holden@Atheros.com>
Cc: Kathy Giori <Kathy.Giori@Atheros.com>
Patchwork: https://patchwork.linux-mips.org/patch/1947/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
In order not to be left behind, we add jump label support for MIPS.
Tested on 64-bit big endian (Octeon), and 32-bit little endian
(malta/qemu).
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jason Baron <jbaron@redhat.com>
Patchwork: https://patchwork.linux-mips.org/patch/1923/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
On the off chance that uasm ever warns about overflow, there is no way
to know what the offending instruction is.
Change the printks to WARNs, so we can get a nice stack trace. It has
the added benefit of being much more noticeable than the short single
line warning message, so is less likely to be ignored.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1905/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Octeon can use scratch registers in the TLB handlers. Octeon II can
use LDX instructions.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1904/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
If the CPU supports BBIT0 and BBIT1, use them in TLB handlers as they
are more efficient than an AND followed by an branch and then
restoring the clobbered register.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1873/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
these are already defined, but declaring them allow them to be used
outside of uasm.c.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1872/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This patch adds a generic solution to support multiple machines based on
a given SoC within a single kernel image. It is implemented already for
several other architectures but MIPS has no generic support for that yet.
[Ralf: This competes with DT but DT is a much more complex solution and this
code has been used by OpenWRT for a long time so for now DT is a bad reason
to stop the merge but longer term this should be migrated to DT.]
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: kaloz@openwrt.org
Cc: Luis R. Rodriguez <lrodriguez@atheros.com>
Cc: Cliff Holden <Cliff.Holden@Atheros.com>
Patchwork: https://patchwork.linux-mips.org/patch/1814/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6:
ALSA: hda - Fix initialization for HP 2011 notebooks
ALSA: hda - Add support for VMware controller
ALSA: hda - consitify string arrays
ALSA: hda - Add add multi-streaming playback for AD1988
ASoC: EP93xx: fixed LRCLK rate and DMA oper. in I2S code
ASoC: WM8990: msleep() takes milliseconds not jiffies
ALSA : au88x0 - Limit number of channels to fix Oops via OSS emu
ALSA: constify functions in ac97
ASoC: WL1273 FM radio: Fix breakage with MFD API changes
ALSA: hda - More coverage for odd-number channels elimination for HDMI
ALSA: hda - Store PCM parameters properly in HDMI open callback
ALSA: hda - Rearrange fixup struct in patch_realtek.c
ALSA: oxygen: Xonar DG: fix CS4245 register writes
ALSA: hda - Suppress the odd number of channels for HDMI
ALSA: hda - Add fixup-call in init callback
ALSA: hda - Reorganize fixup structure for Realtek
ALSA: hda - Apply Sony VAIO hweq fixup only once
ALSA: hda - Apply mario fixup only once
ALSA: hda - Remove unused fixup entry for ALC262
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu: (25 commits)
m68knommu: fix broken setting of irq_chip and handler
m68knommu: switch to using -mcpu= flags for ColdFire targets
m68knommu: arch/m68knommu/Kconfig whitespace cleanup
m68knommu: create optimal separate instruction and data cache for ColdFire
m68knommu: support ColdFire caches that do copyback and write-through
m68knommu: support version 2 ColdFire split cache
m68knommu: make cache push code ColdFire generic
m68knommu: clean up ColdFire cache control code
m68knommu: move inclusion of ColdFire v4 cache registers
m68knommu: merge bit definitions for version 3 ColdFire cache controller
m68knommu: create bit definitions for the version 2 ColdFire cache controller
m68knommu: remove empty __iounmap() it is no used
m68knommu: remove kernel_map() code, it is not used
m68knommu: remove do_page_fault(), it is not used
m68knommu: use user stack pointer hardware on some ColdFire cores
m68knommu: remove command line printing DEBUG
m68knommu: remove fasthandler interrupt code
m68knommu: move UART addressing to part specific includes
m68knommu: fix clock rate value reported for ColdFire 54xx parts
m68knommu: move ColdFire CPU names into their headers
...
* 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
perf tools: Fix tracepoint id to string perf.data header table
perf tools: Fix handling of wildcards in tracepoint event selectors
powerpc: perf: Fix frequency calculation for overflowing counters
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6:
autofs4: clean ->d_release() and autofs4_free_ino() up
autofs4: split autofs4_init_ino()
autofs4: mkdir and symlink always get a dentry that had passed lookup
autofs4: autofs4_get_inode() doesn't need autofs_info * argument anymore
autofs4: kill ->size in autofs_info
autofs4: pass mode to autofs4_get_inode() explicitly
autofs4: autofs4_mkroot() is not different from autofs4_init_ino()
autofs4: keep symlink body in inode->i_private
autofs4 - fix debug print in autofs4_lookup()
vfs - fix dentry ref count in do_lookup()
autofs4 - fix get_next_positive_dentry()
Linus reported that the RCU lockdep annotation bits triggered for this
rcu_dereference() because we're not holding rcu_read_lock().
Going over the code I cannot convince myself its correct:
- holding a ref on the parent_ctx, doesn't avoid it being uncloned
concurrently (as the comment says), so we can race with a free.
- holding parent_ctx->mutex doesn't avoid the above free from taking
place either, it would at best avoid parent_ctx from being freed.
I.e. the warning is correct. To fix the bug, serialize against the
unclone_ctx() call by extending the reach of the parent_ctx->lock.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Justin TerAvest
Vivek Goyal
Stephen M. Cameron
Tracey Dent
Sergey Senozhatsky
Tao Ma
Linus Torvalds
Guenter Roeck
Oleg Nesterov
Aurelien Jarno
David Daney
Gabor Juhos
Joe Perches
Peter Zijlstra