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Rik van Riel 984d74a720 sysrq: rcu-ify __handle_sysrq 
Echoing values into /proc/sysrq-trigger seems to be a popular way to get
information out of the kernel.  However, dumping information about
thousands of processes, or hundreds of CPUs to serial console can result
in IRQs being blocked for minutes, resulting in various kinds of cascade
failures.

The most common failure is due to interrupts being blocked for a very
long time.  This can lead to things like failed IO requests, and other
things the system cannot easily recover from.

This problem is easily fixable by making __handle_sysrq use RCU instead
of spin_lock_irqsave.

This leaves the warning that RCU grace periods have not elapsed for a
long time, but the system will come back from that automatically.

It also leaves sysrq-from-irq-context when the sysrq keys are pressed,
but that is probably desired since people want that to work in
situations where the system is already hosed.

The callers of register_sysrq_key and unregister_sysrq_key appear to be
capable of sleeping.

Signed-off-by: Rik van Riel <riel@redhat.com>
Reported-by: Madper Xie <cxie@redhat.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2014-06-06 16:08:17 -07:00
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accessibility
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acpi ACPI and power management updates for 3.16-rc1 2014-06-04 08:57:16 -07:00
amba
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ata Merge branch 'for-3.15-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata 2014-05-21 18:35:42 +09:00
atm
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auxdisplay
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base cma: increase CMA_ALIGNMENT upper limit to 12 2014-06-04 16:54:08 -07:00
bcma
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block Merge branch 'akpm' (patchbomb from Andrew) into next 2014-06-04 16:55:13 -07:00
bluetooth TTY/Serial driver patches for 3.16-rc1 2014-06-03 09:01:02 -07:00
bus ARM: SoC driver changes 2014-06-02 16:35:49 -07:00
cdrom cdrom: convert use of typedef ctl_table to struct ctl_table 2014-06-06 16:08:15 -07:00
char random: convert use of typedef ctl_table to struct ctl_table 2014-06-06 16:08:15 -07:00
clk DeviceTree for 3.16: 2014-06-04 10:02:38 -07:00
clocksource Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-04 15:57:20 -07:00
connector Char / misc driver patches for 3.16-rc1 2014-06-03 08:06:56 -07:00
cpufreq ACPI and power management updates for 3.16-rc1 2014-06-04 08:57:16 -07:00
cpuidle ACPI and power management updates for 3.16-rc1 2014-06-04 08:57:16 -07:00
crypto crypto/nx/nx-842: dev_set_drvdata can no longer fail 2014-05-28 13:39:51 -07:00
dca
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devfreq PM / devfreq: remove checks for CONFIG_EXYNOS_ASV 2014-05-24 22:33:51 +09:00
dio
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dma ARM: SoC driver changes 2014-06-02 16:35:49 -07:00
edac PCI changes for the v3.16 merge window: 2014-06-02 12:15:19 -07:00
eisa
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extcon
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firewire sound updates for 3.16-rc1 2014-06-04 09:08:25 -07:00
firmware Merge branch 'arm64-efi-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-05 13:15:32 -07:00
fmc
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gpio This is the bulk of GPIO changes for the v3.16 series: 2014-06-02 08:46:03 -07:00
gpu drm/exynos: call find_vma with the mmap_sem held 2014-06-04 16:54:00 -07:00
hid Merge branches 'for-3.16/i2c-hid', 'for-3.16/rmi4', 'for-3.16/sony' and 'for-3.16/thingm' into for-linus 2014-06-04 13:09:43 +02:00
hsi
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hv hv: use correct order when freeing monitor_pages 2014-05-28 13:45:15 -07:00
hwmon New driver for NCT6683D 2014-06-03 11:09:43 -07:00
hwspinlock
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i2c
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ide
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idle
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iio Staging driver patches for 3.16-rc1 2014-06-03 08:34:00 -07:00
infiniband Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2014-05-23 15:29:43 -07:00
input ARM: SoC updates for 3.16 (part 1) 2014-06-02 16:15:12 -07:00
iommu Merge branch 'akpm' (patchbomb from Andrew) into next 2014-06-04 16:55:13 -07:00
ipack
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irqchip Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-04 15:59:13 -07:00
isdn
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leds Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid into next 2014-06-04 08:52:36 -07:00
lguest
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macintosh
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mailbox
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mcb mcb: Add support for shared PCI IRQs 2014-05-27 17:38:11 -07:00
md Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 12:57:53 -07:00
media Merge branch 'v4l_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media into next 2014-06-04 14:24:30 -07:00
memory
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memstick
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message
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mfd sound updates for 3.16-rc1 2014-06-04 09:08:25 -07:00
misc Merge branch 'x86-uv-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 15:48:23 -07:00
mmc Updates for mmci driver: 2014-06-02 09:22:24 -07:00
mtd Merge branch 'for-3.16/core' of git://git.kernel.dk/linux-block into next 2014-06-02 09:29:34 -07:00
net Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-04 15:59:13 -07:00
nfc
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ntb
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nubus kernel/printk: use symbolic defines for console loglevels 2014-06-04 16:54:17 -07:00
of Microblaze patches for 3.16-rc1 2014-06-05 16:15:33 -07:00
oprofile
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parisc
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parport parport: convert use of typedef ctl_table to struct ctl_table 2014-06-06 16:08:15 -07:00
pci Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-04 15:59:13 -07:00
pcmcia pcmcia: Use pci_is_bridge() to simplify code 2014-05-27 14:58:24 -06:00
phy
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pinctrl This is the bulk of pin control changes for the v3.16 2014-06-03 11:20:32 -07:00
platform ACPI and power management updates for 3.16-rc1 2014-06-04 08:57:16 -07:00
pnp Merge branches 'pnp', 'powercap', 'pm-runtime' and 'pm-opp' 2014-06-03 23:13:00 +02:00
power ACPI and power management updates for 3.16-rc1 2014-06-04 08:57:16 -07:00
powercap
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pps
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ps3
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ptp
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pwm
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rapidio rapidio/tsi721: use pci_enable_msix_exact() instead of pci_enable_msix() 2014-06-06 16:08:13 -07:00
regulator regulator: Updates for v3.16 2014-06-03 11:44:48 -07:00
remoteproc
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reset ARM: SoC driver changes 2014-06-02 16:35:49 -07:00
rpmsg
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rtc drivers/rtc/rtc-pxa.c: make of_device_id array const 2014-06-06 16:08:09 -07:00
s390 At over 200 commits, covering almost all supported architectures, this 2014-06-04 08:47:12 -07:00
sbus
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scsi scsi: convert use of typedef ctl_table to struct ctl_table 2014-06-06 16:08:16 -07:00
sfi
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sh Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-04 15:59:13 -07:00
sn
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soc soc: qcom: fix of_device_id table 2014-05-26 21:27:09 +02:00
spi Merge remote-tracking branch 'spi/topic/workqueue' into spi-next 2014-06-02 17:08:43 +01:00
spmi
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ssb
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staging Merge branch 'v4l_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media into next 2014-06-04 14:24:30 -07:00
target Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 12:57:53 -07:00
tc
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thermal
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tty sysrq: rcu-ify __handle_sysrq 2014-06-06 16:08:17 -07:00
uio uio: fix vma io range check in mmap 2014-05-27 14:11:06 -07:00
usb Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-04 15:59:13 -07:00
uwb uwb: fix variable set but not used warnings 2014-05-27 15:18:48 -07:00
vfio driver core: dev_set_drvdata can no longer fail 2014-05-27 13:40:51 -07:00
vhost
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video fbdev changes for 3.16 (omap) 2014-06-04 09:07:08 -07:00
virt
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virtio
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vlynq
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vme
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w1 Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 12:57:53 -07:00
watchdog
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xen Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-04 15:59:13 -07:00
zorro
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Kconfig soc: Introduce drivers/soc place-holder for SOC specific drivers 2014-05-23 11:37:46 -05:00
Makefile Char / misc driver patches for 3.16-rc1 2014-06-03 08:06:56 -07:00