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Peter Zijlstra 1cef1150ef kthread, sched/core: Fix kthread_parkme() (again...) 
Gaurav reports that commit:

  85f1abe001 ("kthread, sched/wait: Fix kthread_parkme() completion issue")

isn't working for him. Because of the following race:

> controller Thread                               CPUHP Thread
> takedown_cpu
> kthread_park
> kthread_parkme
> Set KTHREAD_SHOULD_PARK
>                                                 smpboot_thread_fn
>                                                 set Task interruptible
>
>
> wake_up_process
>  if (!(p->state & state))
>                 goto out;
>
>                                                 Kthread_parkme
>                                                 SET TASK_PARKED
>                                                 schedule
>                                                 raw_spin_lock(&rq->lock)
> ttwu_remote
> waiting for __task_rq_lock
>                                                 context_switch
>
>                                                 finish_lock_switch
>
>
>
>                                                 Case TASK_PARKED
>                                                 kthread_park_complete
>
>
> SET Running

Furthermore, Oleg noticed that the whole scheduler TASK_PARKED
handling is buggered because the TASK_DEAD thing is done with
preemption disabled, the current code can still complete early on
preemption :/

So basically revert that earlier fix and go with a variant of the
alternative mentioned in the commit. Promote TASK_PARKED to special
state to avoid the store-store issue on task->state leading to the
WARN in kthread_unpark() -> __kthread_bind().

But in addition, add wait_task_inactive() to kthread_park() to ensure
the task really is PARKED when we return from kthread_park(). This
avoids the whole kthread still gets migrated nonsense -- although it
would be really good to get this done differently.

Reported-by: Gaurav Kohli <gkohli@codeaurora.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 85f1abe001 ("kthread, sched/wait: Fix kthread_parkme() completion issue")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-03 09:17:30 +02:00
arch Merge branch 'parisc-4.18-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux 2018-06-30 14:16:30 -07:00
block for-linus-20180629 2018-06-30 10:47:46 -07:00
certs certs/blacklist: fix const confusion 2018-06-26 09:43:03 -07:00
crypto Revert changes to convert to ->poll_mask() and aio IOCB_CMD_POLL 2018-06-28 10:40:47 -07:00
Documentation USB fixes for 4.18-rc3 2018-07-01 11:50:16 -07:00
drivers Staging/IIO fixes for 4.18-rc3 2018-07-01 12:20:20 -07:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs for-4.18-rc2-tag 2018-07-01 12:38:16 -07:00
include kthread, sched/core: Fix kthread_parkme() (again...) 2018-07-03 09:17:30 +02:00
init Kbuild fixes for v4.18 2018-06-30 13:05:30 -07:00
ipc ipc: use new return type vm_fault_t 2018-06-15 07:55:25 +09:00
kernel kthread, sched/core: Fix kthread_parkme() (again...) 2018-07-03 09:17:30 +02:00
lib for-linus-20180629 2018-06-30 10:47:46 -07:00
LICENSES LICENSES: Add Linux-OpenIB license text 2018-04-27 16:41:53 -06:00
mm slub: fix failure when we delete and create a slab cache 2018-06-28 11:16:44 -07:00
net net: handle NULL ->poll gracefully 2018-06-29 06:51:51 -07:00
samples VFIO updates for v4.18 2018-06-12 13:11:26 -07:00
scripts Kbuild fixes for v4.18 2018-06-30 13:05:30 -07:00
security selinux/stable-4.18 PR 20180629 2018-06-30 11:15:12 -07:00
sound ALSA: seq: Fix UBSAN warning at SNDRV_SEQ_IOCTL_QUERY_NEXT_CLIENT ioctl 2018-06-25 11:18:04 +02:00
tools Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-06-30 11:42:14 -07:00
usr kbuild: rename built-in.o to built-in.a 2018-03-26 02:01:19 +09:00
virt KVM: arm64: Prevent KVM_COMPAT from being selected 2018-06-21 17:17:50 +01:00
.clang-format clang-format: add configuration file 2018-04-11 10:28:35 -07:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap Merge branch 'asoc-4.17' into asoc-4.18 for compress dependencies 2018-04-26 12:24:28 +01:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS/CREDITS: Drop METAG ARCHITECTURE 2018-03-05 16:34:24 +00:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: add basic helper macros to scripts/Kconfig.include 2018-05-29 03:31:19 +09:00
MAINTAINERS proc: add Alexey to MAINTAINERS 2018-06-28 11:16:44 -07:00
Makefile Linux 4.18-rc3 2018-07-01 16:04:53 -07:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

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

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

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.