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Paul E. McKenney f937759c74 rcu: Protect ->defer_qs_iw_pending from data race 
[ Upstream commit 90c09d57ca ]

On kernels built with CONFIG_IRQ_WORK=y, when rcu_read_unlock() is
invoked within an interrupts-disabled region of code [1], it will invoke
rcu_read_unlock_special(), which uses an irq-work handler to force the
system to notice when the RCU read-side critical section actually ends.
That end won't happen until interrupts are enabled at the soonest.

In some kernels, such as those booted with rcutree.use_softirq=y, the
irq-work handler is used unconditionally.

The per-CPU rcu_data structure's ->defer_qs_iw_pending field is
updated by the irq-work handler and is both read and updated by
rcu_read_unlock_special().  This resulted in the following KCSAN splat:

------------------------------------------------------------------------

BUG: KCSAN: data-race in rcu_preempt_deferred_qs_handler / rcu_read_unlock_special

read to 0xffff96b95f42d8d8 of 1 bytes by task 90 on cpu 8:
 rcu_read_unlock_special+0x175/0x260
 __rcu_read_unlock+0x92/0xa0
 rt_spin_unlock+0x9b/0xc0
 __local_bh_enable+0x10d/0x170
 __local_bh_enable_ip+0xfb/0x150
 rcu_do_batch+0x595/0xc40
 rcu_cpu_kthread+0x4e9/0x830
 smpboot_thread_fn+0x24d/0x3b0
 kthread+0x3bd/0x410
 ret_from_fork+0x35/0x40
 ret_from_fork_asm+0x1a/0x30

write to 0xffff96b95f42d8d8 of 1 bytes by task 88 on cpu 8:
 rcu_preempt_deferred_qs_handler+0x1e/0x30
 irq_work_single+0xaf/0x160
 run_irq_workd+0x91/0xc0
 smpboot_thread_fn+0x24d/0x3b0
 kthread+0x3bd/0x410
 ret_from_fork+0x35/0x40
 ret_from_fork_asm+0x1a/0x30

no locks held by irq_work/8/88.
irq event stamp: 200272
hardirqs last  enabled at (200272): [<ffffffffb0f56121>] finish_task_switch+0x131/0x320
hardirqs last disabled at (200271): [<ffffffffb25c7859>] __schedule+0x129/0xd70
softirqs last  enabled at (0): [<ffffffffb0ee093f>] copy_process+0x4df/0x1cc0
softirqs last disabled at (0): [<0000000000000000>] 0x0

------------------------------------------------------------------------

The problem is that irq-work handlers run with interrupts enabled, which
means that rcu_preempt_deferred_qs_handler() could be interrupted,
and that interrupt handler might contain an RCU read-side critical
section, which might invoke rcu_read_unlock_special().  In the strict
KCSAN mode of operation used by RCU, this constitutes a data race on
the ->defer_qs_iw_pending field.

This commit therefore disables interrupts across the portion of the
rcu_preempt_deferred_qs_handler() that updates the ->defer_qs_iw_pending
field.  This suffices because this handler is not a fast path.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2025-08-28 16:22:42 +02:00
arch s390/time: Use monotonic clock in get_cycles() 2025-08-28 16:22:42 +02:00
block blk-iocost: do not WARN if iocg was already offlined 2025-05-02 07:41:07 +02:00
certs
crypto crypto: xts - Only add ecb if it is not already there 2025-06-27 11:04:01 +01:00
Documentation Documentation: ACPI: Fix parent device references 2025-08-28 16:22:39 +02:00
drivers net: ag71xx: Add missing check after DMA map 2025-08-28 16:22:42 +02:00
fs better lockdep annotations for simple_recursive_removal() 2025-08-28 16:22:40 +02:00
include io_uring: don't use int for ABI 2025-08-28 16:22:38 +02:00
init bpf: Clean up sockmap related Kconfigs 2025-06-27 11:04:09 +01:00
io_uring io_uring: fix possible deadlock in io_register_iowq_max_workers() 2024-11-17 14:59:39 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:04:14 +01:00
kernel rcu: Protect ->defer_qs_iw_pending from data race 2025-08-28 16:22:42 +02:00
lib lib: test_objagg: Set error message in check_expect_hints_stats() 2025-07-17 18:27:47 +02:00
LICENSES
mm mm/hmm: move pmd_to_hmm_pfn_flags() to the respective #ifdeffery 2025-08-28 16:22:38 +02:00
net wifi: cfg80211: reject HTC bit for management frames 2025-08-28 16:22:42 +02:00
samples samples: mei: Fix building on musl libc 2025-08-28 16:22:32 +02:00
scripts kconfig: qconf: fix ConfigList::updateListAllforAll() 2025-08-28 16:22:36 +02:00
security securityfs: don't pin dentries twice, once is enough... 2025-08-28 16:22:40 +02:00
sound ASoC: codecs: rt5640: Retry DEVICE_ID verification 2025-08-28 16:22:42 +02:00
tools ktest.pl: Prevent recursion of default variable options 2025-08-28 16:22:42 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-06-27 11:04:11 +01:00
virt KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-10-22 15:39:24 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:07:59 +02:00
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS platform: Add Surface platform directory 2025-06-27 11:04:19 +01:00
Makefile Linux 5.10.240 2025-07-17 18:28:01 +02:00
README

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 Restructured Text 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.