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Christian Brauner 123bcd8f42 pidfs: improve multi-threaded exec and premature thread-group leader exit polling 
[ Upstream commit 0fb482728b ]

This is another attempt trying to make pidfd polling for multi-threaded
exec and premature thread-group leader exit consistent.

A quick recap of these two cases:

(1) During a multi-threaded exec by a subthread, i.e., non-thread-group
    leader thread, all other threads in the thread-group including the
    thread-group leader are killed and the struct pid of the
    thread-group leader will be taken over by the subthread that called
    exec. IOW, two tasks change their TIDs.

(2) A premature thread-group leader exit means that the thread-group
    leader exited before all of the other subthreads in the thread-group
    have exited.

Both cases lead to inconsistencies for pidfd polling with PIDFD_THREAD.
Any caller that holds a PIDFD_THREAD pidfd to the current thread-group
leader may or may not see an exit notification on the file descriptor
depending on when poll is performed. If the poll is performed before the
exec of the subthread has concluded an exit notification is generated
for the old thread-group leader. If the poll is performed after the exec
of the subthread has concluded no exit notification is generated for the
old thread-group leader.

The correct behavior would be to simply not generate an exit
notification on the struct pid of a subhthread exec because the struct
pid is taken over by the subthread and thus remains alive.

But this is difficult to handle because a thread-group may exit
prematurely as mentioned in (2). In that case an exit notification is
reliably generated but the subthreads may continue to run for an
indeterminate amount of time and thus also may exec at some point.

So far there was no way to distinguish between (1) and (2) internally.
This tiny series tries to address this problem by discarding
PIDFD_THREAD notification on premature thread-group leader exit.

If that works correctly then no exit notifications are generated for a
PIDFD_THREAD pidfd for a thread-group leader until all subthreads have
been reaped. If a subthread should exec aftewards no exit notification
will be generated until that task exits or it creates subthreads and
repeates the cycle.

Co-Developed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20250320-work-pidfs-thread_group-v4-1-da678ce805bf@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-05-29 11:02:09 +02:00
arch riscv: Allow NOMMU kernels to access all of RAM 2025-05-29 11:02:05 +02:00
block block: fix race between set_blocksize and read paths 2025-05-29 11:02:01 +02:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: Kconfig - Select LIB generic option 2025-05-02 07:59:33 +02:00
Documentation netlink: specs: tc: all actions are indexed arrays 2025-05-22 14:29:42 +02:00
drivers libnvdimm/labels: Fix divide error in nd_label_data_init() 2025-05-29 11:02:09 +02:00
fs pidfs: improve multi-threaded exec and premature thread-group leader exit polling 2025-05-29 11:02:09 +02:00
include tracing: Mark binary printing functions with __printf() attribute 2025-05-29 11:02:04 +02:00
init rust: clean Rust 1.88.0's unnecessary_transmutes lint 2025-05-18 08:24:51 +02:00
io_uring io_uring/msg: initialise msg request opcode 2025-05-29 11:02:03 +02:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel pidfs: improve multi-threaded exec and premature thread-group leader exit polling 2025-05-29 11:02:09 +02:00
lib dql: Fix dql->limit value when reset. 2025-05-29 11:02:07 +02:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm/page_alloc: fix race condition in unaccepted memory handling 2025-05-22 14:29:52 +02:00
net Bluetooth: Disable SCO support if READ_VOICE_SETTING is unsupported/broken 2025-05-29 11:02:07 +02:00
rust rust: clean Rust 1.88.0's clippy::uninlined_format_args lint 2025-05-18 08:24:57 +02:00
samples samples/bpf: Fix compilation failure for samples/bpf on LoongArch Fedora 2025-05-29 11:02:01 +02:00
scripts kconfig: merge_config: use an empty file as initfile 2025-05-29 11:02:02 +02:00
security ima: process_measurement() needlessly takes inode_lock() on MAY_READ 2025-05-29 11:02:00 +02:00
sound ASoC: codecs: wsa883x: Correct VI sense channel mask 2025-05-29 11:02:06 +02:00
tools tools/build: Don't pass test log files to linker 2025-05-29 11:02:08 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: Add member to struct kvm_gfn_range to indicate private/shared 2025-05-22 14:29:36 +02:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-18 08:24:51 +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 rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.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 Alexey Makhalov's email address 2025-05-22 14:29:46 +02:00
Makefile Linux 6.12.30 2025-05-22 14:29:54 +02:00
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.