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Frederic Weisbecker 8e84693621 rcutorture: Fix ksoftirqd boosting timing and iteration 
[ Upstream commit 3002153a91 ]

The RCU priority boosting can fail in two situations:

1) If (nr_cpus= > maxcpus=), which means if the total number of CPUs
is higher than those brought online at boot, then torture_onoff() may
later bring up CPUs that weren't online on boot. Now since rcutorture
initialization only boosts the ksoftirqds of the CPUs that have been
set online on boot, the CPUs later set online by torture_onoff won't
benefit from the boost, making RCU priority boosting fail.

2) The ksoftirqd kthreads are boosted after the creation of
rcu_torture_boost() kthreads, which opens a window large enough for these
rcu_torture_boost() kthreads to wait (despite running at FIFO priority)
for ksoftirqds that are still running at SCHED_NORMAL priority.

The issues can trigger for example with:

	./kvm.sh --configs TREE01 --kconfig "CONFIG_RCU_BOOST=y"

	[   34.968561] rcu-torture: !!!
	[   34.968627] ------------[ cut here ]------------
	[   35.014054] WARNING: CPU: 4 PID: 114 at kernel/rcu/rcutorture.c:1979 rcu_torture_stats_print+0x5ad/0x610
	[   35.052043] Modules linked in:
	[   35.069138] CPU: 4 PID: 114 Comm: rcu_torture_sta Not tainted 5.18.0-rc1 #1
	[   35.096424] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a-rebuilt.opensuse.org 04/01/2014
	[   35.154570] RIP: 0010:rcu_torture_stats_print+0x5ad/0x610
	[   35.198527] Code: 63 1b 02 00 74 02 0f 0b 48 83 3d 35 63 1b 02 00 74 02 0f 0b 48 83 3d 21 63 1b 02 00 74 02 0f 0b 48 83 3d 0d 63 1b 02 00 74 02 <0f> 0b 83 eb 01 0f 8e ba fc ff ff 0f 0b e9 b3 fc ff f82
	[   37.251049] RSP: 0000:ffffa92a0050bdf8 EFLAGS: 00010202
	[   37.277320] rcu: De-offloading 8
	[   37.290367] RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000001
	[   37.290387] RDX: 0000000000000000 RSI: 00000000ffffbfff RDI: 00000000ffffffff
	[   37.290398] RBP: 000000000000007b R08: 0000000000000000 R09: c0000000ffffbfff
	[   37.290407] R10: 000000000000002a R11: ffffa92a0050bc18 R12: ffffa92a0050be20
	[   37.290417] R13: ffffa92a0050be78 R14: 0000000000000000 R15: 000000000001bea0
	[   37.290427] FS:  0000000000000000(0000) GS:ffff96045eb00000(0000) knlGS:0000000000000000
	[   37.290448] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
	[   37.290460] CR2: 0000000000000000 CR3: 000000001dc0c000 CR4: 00000000000006e0
	[   37.290470] Call Trace:
	[   37.295049]  <TASK>
	[   37.295065]  ? preempt_count_add+0x63/0x90
	[   37.295095]  ? _raw_spin_lock_irqsave+0x12/0x40
	[   37.295125]  ? rcu_torture_stats_print+0x610/0x610
	[   37.295143]  rcu_torture_stats+0x29/0x70
	[   37.295160]  kthread+0xe3/0x110
	[   37.295176]  ? kthread_complete_and_exit+0x20/0x20
	[   37.295193]  ret_from_fork+0x22/0x30
	[   37.295218]  </TASK>

Fix this with boosting the ksoftirqds kthreads from the boosting
hotplug callback itself and before the boosting kthreads are created.

Fixes: ea6d962e80 ("rcutorture: Judge RCU priority boosting on grace periods, not callbacks")
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-08-17 14:40:52 +02:00
arch arm64: Expand ESR_ELx_WFx_ISS_TI to match its ARMv8.7 definition 2022-08-17 14:40:42 +02:00
block blk-mq: don't create hctx debugfs dir until q->debugfs_dir is created 2022-08-17 14:40:38 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:28:03 +02:00
crypto crypto: memneq - move into lib/ 2022-06-22 14:28:06 +02:00
Documentation dm writecache: count number of blocks discarded, not number of discard bios 2022-08-17 14:40:39 +02:00
drivers drm/radeon: fix incorrrect SPDX-License-Identifiers 2022-08-17 14:40:51 +02:00
fs io_uring: move to separate directory 2022-08-17 14:40:41 +02:00
include raw: convert raw sockets to RCU 2022-08-17 14:40:49 +02:00
init stack: Declare {randomize_,}kstack_offset to fix Sparse warnings 2022-08-17 14:40:36 +02:00
io_uring io_uring: Don't require reinitable percpu_ref 2022-08-17 14:40:42 +02:00
ipc ipc/mqueue: use get_tree_nodev() in mqueue_get_tree() 2022-06-09 10:30:30 +02:00
kernel rcutorture: Fix ksoftirqd boosting timing and iteration 2022-08-17 14:40:52 +02:00
lib lib: overflow: Do not define 64-bit tests on 32-bit 2022-08-17 14:40:35 +02:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm page_alloc: fix invalid watermark check on a negative value 2022-08-03 12:05:28 +02:00
net raw: Fix mixed declarations error in raw_icmp_error(). 2022-08-17 14:40:49 +02:00
samples samples/landlock: Format with clang-format 2022-06-09 10:30:46 +02:00
scripts kbuild: Fix include path in scripts/Makefile.modpost 2022-08-17 14:40:34 +02:00
security selinux: Add boundary check in put_entry() 2022-08-17 14:40:26 +02:00
sound ALSA: hda/realtek: Add a quirk for HP OMEN 15 (8786) mute LED 2022-08-17 14:40:07 +02:00
tools torture: Adjust to again produce debugging information 2022-08-17 14:40:52 +02:00
usr Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
virt KVM: Do not incorporate page offset into gfn=>pfn cache user address 2022-08-17 14:40:06 +02:00
.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 hotfixes for 5.18-rc7 2022-05-13 10:22:37 -07:00
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 io_uring: move to separate directory 2022-08-17 14:40:41 +02:00
Makefile io_uring: move to separate directory 2022-08-17 14:40:41 +02:00
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.