kernel/linux
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ synced 2026-11-10 20:48:12 +00:00
Code Issues Releases Packages Activity
No description
1,313,592 commits 117 branches 5,827 tags 6.3 GiB
  • C 96.8%
  • Assembly 0.9%
  • Rust 0.7%
  • Shell 0.6%
  • Python 0.5%
  • Other 0.3%
Find a file
Frederic Weisbecker 12ead225b7 timers/migration: Fix another race between hotplug and idle entry/exit 
commit b729cc1ec2 upstream.

Commit 10a0e6f3d3 ("timers/migration: Move hierarchy setup into
cpuhotplug prepare callback") fixed a race between idle exit and CPU
hotplug up leading to a wrong "0" value migrator assigned to the top
level. However there is still a situation that remains unhandled:

         [GRP0:0]
        migrator  = TMIGR_NONE
        active    = NONE
        groupmask = 0
        /     \      \
       0       1     2..7
     idle      idle   idle

0) The system is fully idle.

         [GRP0:0]
        migrator  = CPU 0
        active    = CPU 0
        groupmask = 0
        /     \      \
       0       1     2..7
     active   idle   idle

1) CPU 0 is activating. It has done the cmpxchg on the top's ->migr_state
but it hasn't yet returned to __walk_groups().

         [GRP0:0]
        migrator  = CPU 0
        active    = CPU 0, CPU 1
        groupmask = 0
        /     \      \
       0       1     2..7
     active  active  idle

2) CPU 1 is activating. CPU 0 stays the migrator (still stuck in
__walk_groups(), delayed by #VMEXIT for example).

                 [GRP1:0]
              migrator = TMIGR_NONE
              active   = NONE
              groupmask = 0
              /                  \
        [GRP0:0]                      [GRP0:1]
       migrator  = CPU 0           migrator = TMIGR_NONE
       active    = CPU 0, CPU1     active   = NONE
       groupmask = 2               groupmask = 1
       /     \      \
      0       1     2..7                   8
    active  active  idle              !online

3) CPU 8 is preparing to boot. CPUHP_TMIGR_PREPARE is being ran by CPU 1
which has created the GRP0:1 and the new top GRP1:0 connected to GRP0:1
and GRP0:0. The groupmask of GRP0:0 is now 2. CPU 1 hasn't yet
propagated its activation up to GRP1:0.

                 [GRP1:0]
              migrator = 0 (!!!)
              active   = NONE
              groupmask = 0
              /                  \
        [GRP0:0]                  [GRP0:1]
       migrator  = CPU 0           migrator = TMIGR_NONE
       active    = CPU 0, CPU1     active   = NONE
       groupmask = 2               groupmask = 1
       /     \      \
      0       1     2..7                   8
    active  active  idle                !online

4) CPU 0 finally resumed after its #VMEXIT. It's in __walk_groups()
returning from tmigr_cpu_active(). The new top GRP1:0 is visible and
fetched but the freshly updated groupmask of GRP0:0 may not be visible
due to lack of ordering! As a result tmigr_active_up() is called to
GRP0:0 with a child's groupmask of "0". This buggy "0" groupmask then
becomes the migrator for GRP1:0 forever. As a result, timers on a fully
idle system get ignored.

One possible fix would be to define TMIGR_NONE as "0" so that such a
race would have no effect. And after all TMIGR_NONE doesn't need to be
anything else. However this would leave an uncomfortable state machine
where gears happen not to break by chance but are vulnerable to future
modifications.

Keep TMIGR_NONE as is instead and pre-initialize to "1" the groupmask of
any newly created top level. This groupmask is guaranteed to be visible
upon fetching the corresponding group for the 1st time:

_ By the upcoming CPU thanks to CPU hotplug synchronization between the
  control CPU (BP) and the booting one (AP).

_ By the control CPU since the groupmask and parent pointers are
  initialized locally.

_ By all CPUs belonging to the same group than the control CPU because
  they must wait for it to ever become idle before needing to walk to
  the new top. The cmpcxhg() on ->migr_state then makes sure its
  groupmask is visible.

With this pre-initialization, it is guaranteed that if a future top level
is linked to an old one, it is walked through with a valid groupmask.

Fixes: 10a0e6f3d3 ("timers/migration: Move hierarchy setup into cpuhotplug prepare callback")
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20250114231507.21672-2-frederic@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-01-23 17:23:03 +01:00
arch x86/asm: Make serialize() always_inline 2025-01-23 17:22:58 +01:00
block block, bfq: fix waker_bfqq UAF after bfq_split_bfqq() 2025-01-17 13:40:59 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: ecdsa - Avoid signed integer overflow on signature decoding 2024-12-14 20:03:36 +01:00
Documentation fs/writeback: convert wbc_account_cgroup_owner to take a folio 2025-01-17 13:40:33 +01:00
drivers irqchip/gic-v3-its: Don't enable interrupts in its_irq_set_vcpu_affinity() 2025-01-23 17:23:02 +01:00
fs fs/proc: fix softlockup in __read_vmcore (part 2) 2025-01-23 17:23:01 +01:00
include hrtimers: Handle CPU state correctly on hotplug 2025-01-23 17:23:03 +01:00
init Compiler Attributes: disable __counted_by for clang < 19.1.3 2024-12-05 14:02:45 +01:00
io_uring io_uring: don't touch sqd->thread off tw add 2025-01-17 13:40:59 +01:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel timers/migration: Fix another race between hotplug and idle entry/exit 2025-01-23 17:23:03 +01:00
lib maple_tree: reload mas before the second call for mas_empty_area 2025-01-09 13:33:50 +01:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm: vmscan : pgdemote vmstat is not getting updated when MGLRU is enabled. 2025-01-23 17:23:02 +01:00
net net/ncsi: fix locking in Get MAC Address handling 2025-01-23 17:23:00 +01:00
rust rust: kbuild: set bindgen's Rust target version 2024-12-19 18:13:22 +01:00
samples samples/bpf: Fix a resource leak 2024-12-14 20:03:46 +01:00
scripts scripts/sorttable: fix orc_sort_cmp() to maintain symmetry and transitivity 2025-01-09 13:33:50 +01:00
security selinux: ignore unknown extended permissions 2025-01-09 13:33:32 +01:00
sound ALSA: hda/realtek: fixup ASUS H7606W 2025-01-23 17:22:58 +01:00
tools selftests/mm: set allocated memory to non-zero content in cow test 2025-01-23 17:23:01 +01:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt KVM: x86: switch hugepage recovery thread to vhost_task 2024-12-05 14:02:43 +01:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Kbuild updates for v6.12 2024-09-24 13:02:06 -07:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: update location of media main tree 2024-12-05 14:02:42 +01:00
Makefile Linux 6.12.10 2025-01-17 13:41:00 +01:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.