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David Sterba e8d58aef11 btrfs: open code RCU for device name
The RCU protected string is only used for a device name, and RCU is used
so we can print the name and eventually synchronize against the rare
device rename in device_list_add().

We don't need the whole API just for that. Open code all the helpers and
access to the string itself.

Notable change is in device_list_add() when the device name is changed,
which is the only place that can actually happen at the same time as
message prints using the device name under RCU read lock.

Previously there was kfree_rcu() which used the embedded rcu_head to
delay freeing the object depending on the RCU mechanism. Now there's
kfree_rcu_mightsleep() which does not need the rcu_head and waits for
the grace period.

Sleeping is safe in this context and as this is a rare event it won't
interfere with the rest as it's holding the device_list_mutex.

Straightforward changes:

- rcu_string_strdup -> kstrdup
- rcu_str_deref -> rcu_dereference
- drop ->str from safe contexts and use rcu_dereference_raw() so it does
  not trigger RCU validators

Historical notes:

Introduced in 606686eeac ("Btrfs: use rcu to protect device->name")
with a vague reference of the potential problem described in
https://lore.kernel.org/all/20120531155304.GF11775@ZenIV.linux.org.uk/ .

The RCU protection looks like the easiest and most lightweight way of
protecting the rare event of device rename racing device_list_add()
with a random printk() that uses the device name.

Alternatives: a spin lock would require to protect the printk
anyway, a fixed buffer for the name would be eventually wrong in case
the new name is overwritten when being printed, an array switching
pointers and cleaning them up eventually resembles RCU too much.

The cleanups up to this patch should hide special case of RCU to the
minimum that only the name needs rcu_dereference(), which can be further
cleaned up to use btrfs_dev_name().

Reviewed-by: Daniel Vacek <neelx@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2025-07-22 00:09:21 +02:00
arch A single fix for a GCC wreckage, which emits a KCSAN instrumentation call 2025-07-20 11:27:52 -07:00
block block-6.16-20250718 2025-07-18 12:16:13 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: wp512 - Use API partial block handling 2025-06-23 16:56:56 +08:00
Documentation Char/Misc/IIO fixes for 6.16-rc7 2025-07-20 09:03:41 -07:00
drivers i2c-for-6.16-rc7 2025-07-20 12:56:13 -07:00
fs btrfs: open code RCU for device name 2025-07-22 00:09:21 +02:00
include btrfs: tree-log: add and rename extent bits for dirty_log_pages tree 2025-07-21 23:58:01 +02:00
init futex: Temporary disable FUTEX_PRIVATE_HASH 2025-07-01 15:02:05 +02:00
io_uring io_uring-6.16-20250718 2025-07-18 12:21:26 -07:00
ipc - The 3 patch series "hung_task: extend blocking task stacktrace dump to 2025-05-31 19:12:53 -07:00
kernel Tracing fixes for 6.16: 2025-07-20 13:03:31 -07:00
lib maple_tree: fix mt_destroy_walk() on root leaf node 2025-07-09 21:07:52 -07:00
LICENSES LICENSES: add CC0-1.0 license text 2025-05-21 14:54:17 +02:00
mm vfs-6.16-rc7.fixes 2025-07-19 08:47:59 -07:00
net bluetooth pull request for net: 2025-07-17 07:54:49 -07:00
rust Rust fixes for v6.16 (2nd) 2025-07-19 09:22:26 -07:00
samples samples/damon: fix damon sample mtier for start failure 2025-07-09 21:07:55 -07:00
scripts Rust fixes for v6.16 (2nd) 2025-07-19 09:22:26 -07:00
security selinux: change security_compute_sid to return the ssid or tsid on match 2025-06-19 16:13:16 -04:00
sound ASoC: Fixes for v6.16 2025-07-17 14:53:38 +02:00
tools A single fix for the futex selftest code to make 32-bit user space work 2025-07-20 11:22:05 -07:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt KVM: Allow CPU to reschedule while setting per-page memory attributes 2025-06-24 12:20:17 -07:00
.clang-format Linux 6.15-rc5 2025-05-06 16:39:25 +10:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +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 MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore Python compiled bytecode 2025-04-24 10:12:46 -06:00
.mailmap MAINTAINERS: Update Kirill Shutemov's email address for TDX 2025-07-11 07:25:51 -07:00
.pylintrc docs: add a .pylintrc file with sys path for docs scripts 2025-04-09 12:10:33 -06:00
.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 CREDITS: Add entry for Shannon Nelson 2025-06-21 07:34:28 -07:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS Char/Misc/IIO fixes for 6.16-rc7 2025-07-20 09:03:41 -07:00
Makefile Linux 6.16-rc7 2025-07-20 15:18:33 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

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.