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6558749ef3
When running the Rust maple tree kunit tests with lockdep, you may trigger
a warning that looks like this:
lib/maple_tree.c:780 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
no locks held by kunit_try_catch/344.
stack backtrace:
CPU: 3 UID: 0 PID: 344 Comm: kunit_try_catch Tainted: G N 6.19.0-rc1+ #2 NONE
Tainted: [N]=TEST
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x71/0x90
lockdep_rcu_suspicious+0x150/0x190
mas_start+0x104/0x150
mas_find+0x179/0x240
_RINvNtCs5QSdWC790r4_4core3ptr13drop_in_placeINtNtCs1cdwasc6FUb_6kernel10maple_tree9MapleTreeINtNtNtBL_5alloc4kbox3BoxlNtNtB1x_9allocator7KmallocEEECsgxAQYCfdR72_25doctests_kernel_generated+0xaf/0x130
rust_doctest_kernel_maple_tree_rs_0+0x600/0x6b0
? lock_release+0xeb/0x2a0
? kunit_try_catch_run+0x210/0x210
kunit_try_run_case+0x74/0x160
? kunit_try_catch_run+0x210/0x210
kunit_generic_run_threadfn_adapter+0x12/0x30
kthread+0x21c/0x230
? __do_trace_sched_kthread_stop_ret+0x40/0x40
ret_from_fork+0x16c/0x270
? __do_trace_sched_kthread_stop_ret+0x40/0x40
ret_from_fork_asm+0x11/0x20
</TASK>
This is because the destructor of maple tree calls mas_find() without
taking rcu_read_lock() or the spinlock. Doing that is actually ok in this
case since the destructor has exclusive access to the entire maple tree,
but it triggers a lockdep warning. To fix that, take the rcu read lock.
In the future, it's possible that memory reclaim could gain a feature
where it reallocates entries in maple trees even if no user-code is
touching it. If that feature is added, then this use of rcu read lock
would become load-bearing, so I did not make it conditional on lockdep.
We have to repeatedly take and release rcu because the destructor of T
might perform operations that sleep.
Link: https://lkml.kernel.org/r/20251217-maple-drop-rcu-v1-1-702af063573f@google.com
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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