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Tejun Heo 3caa973b7a rcu: Call touch_nmi_watchdog() while printing stall warnings 
When RCU stall warning triggers, it can print out a lot of messages
while holding spinlocks.  If the console device is slow (e.g. an
actual or IPMI serial console), it may end up triggering NMI hard
lockup watchdog like the following.

*** CPU printking while holding RCU spinlock

  PID: 4149739  TASK: ffff881a46baa880  CPU: 13  COMMAND: "CPUThreadPool8"
   #0 [ffff881fff945e48] crash_nmi_callback at ffffffff8103f7d0
   #1 [ffff881fff945e58] nmi_handle at ffffffff81020653
   #2 [ffff881fff945eb0] default_do_nmi at ffffffff81020c36
   #3 [ffff881fff945ed0] do_nmi at ffffffff81020d32
   #4 [ffff881fff945ef0] end_repeat_nmi at ffffffff81956a7e
      [exception RIP: io_serial_in+21]
      RIP: ffffffff81630e55  RSP: ffff881fff943b88  RFLAGS: 00000002
      RAX: 000000000000ca00  RBX: ffffffff8230e188  RCX: 0000000000000000
      RDX: 00000000000002fd  RSI: 0000000000000005  RDI: ffffffff8230e188
      RBP: ffff881fff943bb0   R8: 0000000000000000   R9: ffffffff820cb3c4
      R10: 0000000000000019  R11: 0000000000002000  R12: 00000000000026e1
      R13: 0000000000000020  R14: ffffffff820cd398  R15: 0000000000000035
      ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0000
  --- <NMI exception stack> ---
   #5 [ffff881fff943b88] io_serial_in at ffffffff81630e55
   #6 [ffff881fff943b90] wait_for_xmitr at ffffffff8163175c
   #7 [ffff881fff943bb8] serial8250_console_putchar at ffffffff816317dc
   #8 [ffff881fff943bd8] uart_console_write at ffffffff8162ac00
   #9 [ffff881fff943c08] serial8250_console_write at ffffffff81634691
  #10 [ffff881fff943c80] univ8250_console_write at ffffffff8162f7c2
  #11 [ffff881fff943c90] console_unlock at ffffffff810dfc55
  #12 [ffff881fff943cf0] vprintk_emit at ffffffff810dffb5
  #13 [ffff881fff943d50] vprintk_default at ffffffff810e01bf
  #14 [ffff881fff943d60] vprintk_func at ffffffff810e1127
  #15 [ffff881fff943d70] printk at ffffffff8119a8a4
  #16 [ffff881fff943dd0] print_cpu_stall_info at ffffffff810eb78c
  #17 [ffff881fff943e88] rcu_check_callbacks at ffffffff810ef133
  #18 [ffff881fff943ee8] update_process_times at ffffffff810f3497
  #19 [ffff881fff943f10] tick_sched_timer at ffffffff81103037
  #20 [ffff881fff943f38] __hrtimer_run_queues at ffffffff810f3f38
  #21 [ffff881fff943f88] hrtimer_interrupt at ffffffff810f442b

*** CPU triggering the hardlockup watchdog

  PID: 4149709  TASK: ffff88010f88c380  CPU: 26  COMMAND: "CPUThreadPool35"
   #0 [ffff883fff1059d0] machine_kexec at ffffffff8104a874
   #1 [ffff883fff105a30] __crash_kexec at ffffffff811116cc
   #2 [ffff883fff105af0] __crash_kexec at ffffffff81111795
   #3 [ffff883fff105b08] panic at ffffffff8119a6ae
   #4 [ffff883fff105b98] watchdog_overflow_callback at ffffffff81135dbd
   #5 [ffff883fff105bb0] __perf_event_overflow at ffffffff81186866
   #6 [ffff883fff105be8] perf_event_overflow at ffffffff81192bc4
   #7 [ffff883fff105bf8] intel_pmu_handle_irq at ffffffff8100b265
   #8 [ffff883fff105df8] perf_event_nmi_handler at ffffffff8100489f
   #9 [ffff883fff105e58] nmi_handle at ffffffff81020653
  #10 [ffff883fff105eb0] default_do_nmi at ffffffff81020b94
  #11 [ffff883fff105ed0] do_nmi at ffffffff81020d32
  #12 [ffff883fff105ef0] end_repeat_nmi at ffffffff81956a7e
      [exception RIP: queued_spin_lock_slowpath+248]
      RIP: ffffffff810da958  RSP: ffff883fff103e68  RFLAGS: 00000046
      RAX: 0000000000000000  RBX: 0000000000000046  RCX: 00000000006d0000
      RDX: ffff883fff49a950  RSI: 0000000000d10101  RDI: ffffffff81e54300
      RBP: ffff883fff103e80   R8: ffff883fff11a950   R9: 0000000000000000
      R10: 000000000e5873ba  R11: 000000000000010f  R12: ffffffff81e54300
      R13: 0000000000000000  R14: ffff88010f88c380  R15: ffffffff81e54300
      ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
  --- <NMI exception stack> ---
  #13 [ffff883fff103e68] queued_spin_lock_slowpath at ffffffff810da958
  #14 [ffff883fff103e70] _raw_spin_lock_irqsave at ffffffff8195550b
  #15 [ffff883fff103e88] rcu_check_callbacks at ffffffff810eed18
  #16 [ffff883fff103ee8] update_process_times at ffffffff810f3497
  #17 [ffff883fff103f10] tick_sched_timer at ffffffff81103037
  #18 [ffff883fff103f38] __hrtimer_run_queues at ffffffff810f3f38
  #19 [ffff883fff103f88] hrtimer_interrupt at ffffffff810f442b
  --- <IRQ stack> ---

Avoid spuriously triggering NMI hardlockup watchdog by touching it
from the print functions.  show_state_filter() shares the same problem
and solution.

v2: Relocate the comment to where it belongs.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 		2018-02-20 16:10:26 -08:00
Documentation sched/isolation: Eliminate NO_HZ_FULL_ALL 2018-02-15 15:40:37 -08:00
LICENSES LICENSES: Add MPL-1.1 license 2018-01-06 10:59:44 -07:00
arch unify {de,}mangle_poll(), get rid of kernel-side POLL... 2018-02-11 14:37:22 -08:00
block vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
certs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
crypto vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
drivers vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
include doc: Fix typo in rcu_head comments 2018-02-20 16:10:25 -08:00
init membarrier: Provide core serializing command, *_SYNC_CORE 2018-02-05 21:35:03 +01:00
ipc vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
kernel rcu: Call touch_nmi_watchdog() while printing stall warnings 2018-02-20 16:10:26 -08:00
lib Kbuild updates for v4.16 (2nd) 2018-02-09 19:32:41 -08:00
mm vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
net vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
samples sample/bpf: fix erspan metadata 2018-02-06 11:32:49 -05:00
scripts Kbuild updates for v4.16 (2nd) 2018-02-09 19:32:41 -08:00
security vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
sound vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
tools doc: Fix typo in rcutorture documentation 2018-02-20 16:10:19 -08:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore scripts/package: snap-pkg target 2017-12-13 00:00:18 +09:00
.mailmap mailmap: update Mark Yao's email address 2018-01-04 16:45:09 -08:00
COPYING
…
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS KVM changes for 4.16 2018-02-10 13:16:35 -08:00
Makefile Linux 4.16-rc1 2018-02-11 15:04:29 -08:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.