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Frederic Weisbecker c597d8cb0d timers/nohz: Last resort update jiffies on nohz_full IRQ entry 
[ Upstream commit 53e87e3cdc ]

When at least one CPU runs in nohz_full mode, a dedicated timekeeper CPU
is guaranteed to stay online and to never stop its tick.

Meanwhile on some rare case, the dedicated timekeeper may be running
with interrupts disabled for a while, such as in stop_machine.

If jiffies stop being updated, a nohz_full CPU may end up endlessly
programming the next tick in the past, taking the last jiffies update
monotonic timestamp as a stale base, resulting in an tick storm.

Here is a scenario where it matters:

0) CPU 0 is the timekeeper and CPU 1 a nohz_full CPU.

1) A stop machine callback is queued to execute somewhere.

2) CPU 0 reaches MULTI_STOP_DISABLE_IRQ while CPU 1 is still in
   MULTI_STOP_PREPARE. Hence CPU 0 can't do its timekeeping duty. CPU 1
   can still take IRQs.

3) CPU 1 receives an IRQ which queues a timer callback one jiffy forward.

4) On IRQ exit, CPU 1 schedules the tick one jiffy forward, taking
   last_jiffies_update as a base. But last_jiffies_update hasn't been
   updated for 2 jiffies since the timekeeper has interrupts disabled.

5) clockevents_program_event(), which relies on ktime_get(), observes
   that the expiration is in the past and therefore programs the min
   delta event on the clock.

6) The tick fires immediately, goto 3)

7) Tick storm, the nohz_full CPU is drown and takes ages to reach
   MULTI_STOP_DISABLE_IRQ, which is the only way out of this situation.

Solve this with unconditionally updating jiffies if the value is stale
on nohz_full IRQ entry. IRQs and other disturbances are expected to be
rare enough on nohz_full for the unconditional call to ktime_get() to
actually matter.

Reported-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20211026141055.57358-2-frederic@kernel.org
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2023-08-16 18:22:04 +02:00
arch alpha: remove __init annotation from exported page_is_ram() 2023-08-16 18:22:03 +02:00
block block/partition: fix signedness issue for Amiga partitions 2023-07-23 13:47:37 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto KEYS: asymmetric: Copy sig and digest in public_key_verify_signature() 2023-06-09 10:32:34 +02:00
Documentation iommu/arm-smmu-v3: Document nesting-related errata 2023-08-11 15:13:49 +02:00
drivers scsi: qedf: Fix firmware halt over suspend and resume 2023-08-16 18:22:03 +02:00
fs btrfs: set cache_block_group_error if we find an error 2023-08-16 18:22:03 +02:00
include netfilter: nf_tables: report use refcount overflow 2023-08-16 18:22:03 +02:00
init x86/mm: Initialize text poking earlier 2023-08-08 19:58:33 +02:00
io_uring io_uring: correct check for O_TMPFILE 2023-08-16 18:21:59 +02:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:28:45 +01:00
kernel timers/nohz: Last resort update jiffies on nohz_full IRQ entry 2023-08-16 18:22:04 +02:00
lib test_firmware: return ENOMEM instead of ENOSPC on failed memory allocation 2023-07-23 13:47:25 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/damon/ops-common: atomically test and clear young on ptes and pmds 2023-07-23 13:47:47 +02:00
net sch_netem: fix issues in netem_change() vs get_dist_table() 2023-08-16 18:22:04 +02:00
samples samples: ftrace: Save required argument registers in sample trampolines 2023-07-23 13:47:55 +02:00
scripts kbuild: Disable GCOV for *.mod.o 2023-07-23 13:47:17 +02:00
security security: keys: Modify mismatched function name 2023-07-27 08:47:01 +02:00
sound ASoC: cs42l51: fix driver to properly autoload with automatic module loading 2023-08-03 10:22:47 +02:00
tools nexthop: Fix infinite nexthop bucket dump when using maximum nexthop ID 2023-08-16 18:22:02 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: Grab a reference to KVM for VM and vCPU stats file descriptors 2023-08-03 10:22:40 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
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 cifs: missing directory in MAINTAINERS file 2023-08-03 10:22:29 +02:00
Makefile Linux 5.15.126 2023-08-11 15:14:00 +02:00
README

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.