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Krister Johansen cbd0d5ecfa dm thin: make get_first_thin use rcu-safe list first function 
commit 80f130bfad upstream.

The documentation in rculist.h explains the absence of list_empty_rcu()
and cautions programmers against relying on a list_empty() ->
list_first() sequence in RCU safe code.  This is because each of these
functions performs its own READ_ONCE() of the list head.  This can lead
to a situation where the list_empty() sees a valid list entry, but the
subsequent list_first() sees a different view of list head state after a
modification.

In the case of dm-thin, this author had a production box crash from a GP
fault in the process_deferred_bios path.  This function saw a valid list
head in get_first_thin() but when it subsequently dereferenced that and
turned it into a thin_c, it got the inside of the struct pool, since the
list was now empty and referring to itself.  The kernel on which this
occurred printed both a warning about a refcount_t being saturated, and
a UBSAN error for an out-of-bounds cpuid access in the queued spinlock,
prior to the fault itself.  When the resulting kdump was examined, it
was possible to see another thread patiently waiting in thin_dtr's
synchronize_rcu.

The thin_dtr call managed to pull the thin_c out of the active thins
list (and have it be the last entry in the active_thins list) at just
the wrong moment which lead to this crash.

Fortunately, the fix here is straight forward.  Switch get_first_thin()
function to use list_first_or_null_rcu() which performs just a single
READ_ONCE() and returns NULL if the list is already empty.

This was run against the devicemapper test suite's thin-provisioning
suites for delete and suspend and no regressions were observed.

Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
Fixes: b10ebd34cc ("dm thin: fix rcu_read_lock being held in code that can sleep")
Cc: stable@vger.kernel.org
Acked-by: Ming-Hung Tsai <mtsai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-01-17 13:40:45 +01:00
arch drivers/perf: riscv: Fix Platform firmware event data 2025-01-17 13:40:45 +01:00
block block: lift bio_is_zone_append to bio.h 2025-01-09 13:33:32 +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 dm thin: make get_first_thin use rcu-safe list first function 2025-01-17 13:40:45 +01:00
fs netfs: Fix read-retry for fs with no ->prepare_read() 2025-01-17 13:40:45 +01:00
include tcp/dccp: allow a connection when sk_max_ack_backlog is zero 2025-01-17 13:40:37 +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/rw: fix downgraded mshot read 2025-01-09 13:33:51 +01:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel fgraph: Add READ_ONCE() when accessing fgraph_array[] 2025-01-09 13:33:52 +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: hugetlb: independent PMD page table shared count 2025-01-09 13:33:54 +01:00
net sched: sch_cake: add bounds checks to host bulk flow fairness counts 2025-01-17 13:40:41 +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 ASoC: mediatek: disable buffer pre-allocation 2025-01-17 13:40:36 +01:00
tools selftests/alsa: Fix circular dependency involving global-timer 2025-01-17 13:40:36 +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 6.12.9 2025-01-09 13:33:55 +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.