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Breno Leitao 06742a3ab8 netpoll: Fix deadlock in memory allocation under spinlock 
[ Upstream commit 327c20c21d ]

Fix a AA deadlock in refill_skbs() where memory allocation while holding
skb_pool->lock can trigger a recursive lock acquisition attempt.

The deadlock scenario occurs when the system is under severe memory
pressure:

1. refill_skbs() acquires skb_pool->lock (spinlock)
2. alloc_skb() is called while holding the lock
3. Memory allocator fails and calls slab_out_of_memory()
4. This triggers printk() for the OOM warning
5. The console output path calls netpoll_send_udp()
6. netpoll_send_udp() attempts to acquire the same skb_pool->lock
7. Deadlock: the lock is already held by the same CPU

Call stack:
  refill_skbs()
    spin_lock_irqsave(&skb_pool->lock)    <- lock acquired
    __alloc_skb()
      kmem_cache_alloc_node_noprof()
        slab_out_of_memory()
          printk()
            console_flush_all()
              netpoll_send_udp()
                skb_dequeue()
                  spin_lock_irqsave(&skb_pool->lock)     <- deadlock attempt

This bug was exposed by commit 248f6571fd ("netpoll: Optimize skb
refilling on critical path") which removed refill_skbs() from the
critical path (where nested printk was being deferred), letting nested
printk being called from inside refill_skbs()

Refactor refill_skbs() to never allocate memory while holding
the spinlock.

Another possible solution to fix this problem is protecting the
refill_skbs() from nested printks, basically calling
printk_deferred_{enter,exit}() in refill_skbs(), then, any nested
pr_warn() would be deferred.

I prefer this approach, given I _think_ it might be a good idea to move
the alloc_skb() from GFP_ATOMIC to GFP_KERNEL in the future, so, having
the alloc_skb() outside of the lock will be necessary step.

There is a possible TOCTOU issue when checking for the pool length, and
queueing the new allocated skb, but, this is not an issue, given that
an extra SKB in the pool is harmless and it will be eventually used.

Signed-off-by: Breno Leitao <leitao@debian.org>
Fixes: 248f6571fd ("netpoll: Optimize skb refilling on critical path")
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20251103-fix_netpoll_aa-v4-1-4cfecdf6da7c@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-11-13 15:37:44 -05:00
arch riscv: ptdump: use seq_puts() in pt_dump_seq_puts() macro 2025-11-13 15:37:41 -05:00
block blk-cgroup: fix possible deadlock while configuring policy 2025-11-13 15:36:52 -05:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: essiv - Check ssize for decryption and in-place encryption 2025-10-19 16:37:14 +02:00
Documentation dt-bindings: display/msm/gmu: Update Adreno 623 bindings 2025-11-13 15:37:16 -05:00
drivers bnxt_en: Fix warning in bnxt_dl_reload_down() 2025-11-13 15:37:43 -05:00
fs btrfs: ensure no dirty metadata is written back for an fs with errors 2025-11-13 15:37:40 -05:00
include scsi: ufs: core: Include UTP error in INT_FATAL_ERRORS 2025-11-13 15:37:37 -05:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:37:27 +02:00
io_uring io_uring/zcrx: account niov arrays to cgroup 2025-11-13 15:36:51 -05:00
ipc vfs-6.17-rc1.mmap_prepare 2025-07-28 13:43:25 -07:00
kernel ring-buffer: Do not warn in ring_buffer_map_get_reader() when reader catches up 2025-11-13 15:37:40 -05:00
lib kunit: Enable PCI on UML without triggering WARN() 2025-11-13 15:36:51 -05:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm treewide: remove MIGRATEPAGE_SUCCESS 2025-10-29 14:10:32 +01:00
net
rust rust: kbuild: treat build_error and rustdoc as kernel objects 2025-11-13 15:37:40 -05:00
samples 15 hotfixes. 11 are cc:stable and the remainder address post-6.16 issues 2025-09-17 21:34:26 -07:00
scripts docs: kernel-doc: avoid script crash on ancient Python 2025-11-13 15:36:58 -05:00
security ima: don't clear IMA_DIGSIG flag when setting or removing non-IMA xattr 2025-11-13 15:37:34 -05:00
sound ASoC: rt722: add settings for rt722VB 2025-11-13 15:37:39 -05:00
tools selftests: netdevsim: Fix ethtool-coalesce.sh fail by installing ethtool-common.sh 2025-11-13 15:37:42 -05:00
usr kbuild: uapi: Strip comments before size type check 2025-11-13 15:37:38 -05:00
virt Merge tag 'kvm-x86-no_assignment-6.17' of https://github.com/kvm-x86/linux into HEAD 2025-07-29 08:36:42 -04:00
.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: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore gitignore: allow .pylintrc to be tracked 2025-07-02 17:10:04 -06:00
.mailmap 7 hotfixes. 4 are cc:stable and the remainder address post-6.16 issues or 2025-09-28 09:32:00 -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 MAINTAINERS: retire Boris from TLS maintainers 2025-08-26 17:36:01 -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 i2c-for-6.17-rc8 2025-09-28 13:19:23 -07:00
Makefile Linux 6.17.7 2025-11-02 22:18:05 +09:00
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.