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Michael Ellerman d2b9be1f4a powerpc/time: Always set decrementer in timer_interrupt() 
This is a partial revert of commit 0faf20a1ad ("powerpc/64s/interrupt:
Don't enable MSR[EE] in irq handlers unless perf is in use").

Prior to that commit, we always set the decrementer in
timer_interrupt(), to clear the timer interrupt. Otherwise we could end
up continuously taking timer interrupts.

When high res timers are enabled there is no problem seen with leaving
the decrementer untouched in timer_interrupt(), because it will be
programmed via hrtimer_interrupt() -> tick_program_event() ->
clockevents_program_event() -> decrementer_set_next_event().

However with CONFIG_HIGH_RES_TIMERS=n or booting with highres=off, we
see a stall/lockup, because tick_nohz_handler() does not cause a
reprogram of the decrementer, leading to endless timer interrupts.
Example trace:

  [    1.898617][    T7] Freeing initrd memory: 2624K^M
  [   22.680919][    C1] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:^M
  [   22.682281][    C1] rcu:     0-....: (25 ticks this GP) idle=073/0/0x1 softirq=10/16 fqs=1050 ^M
  [   22.682851][    C1]  (detected by 1, t=2102 jiffies, g=-1179, q=476)^M
  [   22.683649][    C1] Sending NMI from CPU 1 to CPUs 0:^M
  [   22.685252][    C0] NMI backtrace for cpu 0^M
  [   22.685649][    C0] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.16.0-rc2-00185-g0faf20a1ad16 #145^M
  [   22.686393][    C0] NIP:  c000000000016d64 LR: c000000000f6cca4 CTR: c00000000019c6e0^M
  [   22.686774][    C0] REGS: c000000002833590 TRAP: 0500   Not tainted  (5.16.0-rc2-00185-g0faf20a1ad16)^M
  [   22.687222][    C0] MSR:  8000000000009033 <SF,EE,ME,IR,DR,RI,LE>  CR: 24000222  XER: 00000000^M
  [   22.688297][    C0] CFAR: c00000000000c854 IRQMASK: 0 ^M
  ...
  [   22.692637][    C0] NIP [c000000000016d64] arch_local_irq_restore+0x174/0x250^M
  [   22.694443][    C0] LR [c000000000f6cca4] __do_softirq+0xe4/0x3dc^M
  [   22.695762][    C0] Call Trace:^M
  [   22.696050][    C0] [c000000002833830] [c000000000f6cc80] __do_softirq+0xc0/0x3dc (unreliable)^M
  [   22.697377][    C0] [c000000002833920] [c000000000151508] __irq_exit_rcu+0xd8/0x130^M
  [   22.698739][    C0] [c000000002833950] [c000000000151730] irq_exit+0x20/0x40^M
  [   22.699938][    C0] [c000000002833970] [c000000000027f40] timer_interrupt+0x270/0x460^M
  [   22.701119][    C0] [c0000000028339d0] [c0000000000099a8] decrementer_common_virt+0x208/0x210^M

Possibly this should be fixed in the lowres timing code, but that would
be a generic change and could take some time and may not backport
easily, so for now make the programming of the decrementer unconditional
again in timer_interrupt() to avoid the stall/lockup.

Fixes: 0faf20a1ad ("powerpc/64s/interrupt: Don't enable MSR[EE] in irq handlers unless perf is in use")
Reported-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Link: https://lore.kernel.org/r/20220420141657.771442-1-mpe@ellerman.id.au
2022-04-21 16:10:56 +10:00
arch powerpc/time: Always set decrementer in timer_interrupt() 2022-04-21 16:10:56 +10:00
block for-5.18/block-2022-04-01 2022-04-01 16:20:00 -07:00
certs Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
crypto for-5.18/64bit-pi-2022-03-25 2022-03-26 12:01:35 -07:00
Documentation linux-kselftest-kunit-fixes-5.18-rc2 2022-04-08 15:06:11 -10:00
drivers Serial driver fix for 5.18-rc2 2022-04-10 10:08:50 -10:00
fs Driver core changes for 5.18-rc2 2022-04-10 09:55:09 -10:00
include Driver core changes for 5.18-rc2 2022-04-10 09:55:09 -10:00
init Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
ipc fs: allocate inode by using alloc_inode_sb() 2022-03-22 15:57:03 -07:00
kernel - A couple of fixes to cgroup-related handling of perf events 2022-04-10 07:08:22 -10:00
lib Driver core changes for 5.18-rc2 2022-04-10 09:55:09 -10:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm - Allow the compiler to optimize away unused percpu accesses and change 2022-04-10 06:56:46 -10:00
net NFS client bugfixes for Linux 5.18 2022-04-08 07:39:17 -10:00
samples dma-mapping updates for Linux 5.18 2022-03-29 08:50:14 -07:00
scripts modpost: restore the warning message for missing symbol versions 2022-04-03 03:11:51 +09:00
security hardening updates for v5.18-rc1-fix1 2022-03-31 11:43:01 -07:00
sound sound fixes for 5.18-rc1 2022-04-01 10:32:46 -07:00
tools - Fix the MSI message data struct definition 2022-04-10 07:12:27 -10:00
usr Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
virt KVM: Remove dirty handling from gfn_to_pfn_cache completely 2022-04-02 05:34:41 -04:00
.clang-format genirq/msi: Make interrupt allocation less convoluted 2021-12-16 22:22:20 +01:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: update Vasily Averin's email address 2022-04-08 14:20:36 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS v5.18 first rc pull request 2022-04-08 18:29:02 -10:00
Makefile Linux 5.18-rc2 2022-04-10 14:21:36 -10:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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.

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.