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When getting an LLC CPU mask in the default CPU selection policy, scx_select_cpu_dfl(), a pointer to the sched_domain is dereferenced using rcu_read_lock() without holding rcu_read_lock(). Such an unprotected dereference often causes the following warning and can cause an invalid memory access in the worst case. Therefore, protect dereference of a sched_domain pointer using a pair of rcu_read_lock() and unlock(). [ 20.996135] ============================= [ 20.996345] WARNING: suspicious RCU usage [ 20.996563] 6.11.0-virtme #17 Tainted: G W [ 20.996576] ----------------------------- [ 20.996576] kernel/sched/ext.c:3323 suspicious rcu_dereference_check() usage! [ 20.996576] [ 20.996576] other info that might help us debug this: [ 20.996576] [ 20.996576] [ 20.996576] rcu_scheduler_active = 2, debug_locks = 1 [ 20.996576] 4 locks held by kworker/8:1/140: [ 20.996576] #0: ffff8b18c00dd348 ((wq_completion)pm){+.+.}-{0:0}, at: process_one_work+0x4a0/0x590 [ 20.996576] #1: ffffb3da01f67e58 ((work_completion)(&dev->power.work)){+.+.}-{0:0}, at: process_one_work+0x1ba/0x590 [ 20.996576] #2: ffffffffa316f9f0 (&rcu_state.gp_wq){..-.}-{2:2}, at: swake_up_one+0x15/0x60 [ 20.996576] #3: ffff8b1880398a60 (&p->pi_lock){-.-.}-{2:2}, at: try_to_wake_up+0x59/0x7d0 [ 20.996576] [ 20.996576] stack backtrace: [ 20.996576] CPU: 8 UID: 0 PID: 140 Comm: kworker/8:1 Tainted: G W 6.11.0-virtme #17 [ 20.996576] Tainted: [W]=WARN [ 20.996576] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014 [ 20.996576] Workqueue: pm pm_runtime_work [ 20.996576] Sched_ext: simple (disabling+all), task: runnable_at=-6ms [ 20.996576] Call Trace: [ 20.996576] <IRQ> [ 20.996576] dump_stack_lvl+0x6f/0xb0 [ 20.996576] lockdep_rcu_suspicious.cold+0x4e/0x96 [ 20.996576] scx_select_cpu_dfl+0x234/0x260 [ 20.996576] select_task_rq_scx+0xfb/0x190 [ 20.996576] select_task_rq+0x47/0x110 [ 20.996576] try_to_wake_up+0x110/0x7d0 [ 20.996576] swake_up_one+0x39/0x60 [ 20.996576] rcu_core+0xb08/0xe50 [ 20.996576] ? srso_alias_return_thunk+0x5/0xfbef5 [ 20.996576] ? mark_held_locks+0x40/0x70 [ 20.996576] handle_softirqs+0xd3/0x410 [ 20.996576] irq_exit_rcu+0x78/0xa0 [ 20.996576] sysvec_apic_timer_interrupt+0x73/0x80 [ 20.996576] </IRQ> [ 20.996576] <TASK> [ 20.996576] asm_sysvec_apic_timer_interrupt+0x1a/0x20 [ 20.996576] RIP: 0010:_raw_spin_unlock_irqrestore+0x36/0x70 [ 20.996576] Code: f5 53 48 8b 74 24 10 48 89 fb 48 83 c7 18 e8 11 b4 36 ff 48 89 df e8 99 0d 37 ff f7 c5 00 02 00 00 75 17 9c 58 f6 c4 02 75 2b <65> ff 0d 5b 55 3c 5e 74 16 5b 5d e9 95 8e 28 00 e8 a5 ee 44 ff 9c [ 20.996576] RSP: 0018:ffffb3da01f67d20 EFLAGS: 00000246 [ 20.996576] RAX: 0000000000000002 RBX: ffffffffa4640220 RCX: 0000000000000040 [ 20.996576] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffa1c7b27b [ 20.996576] RBP: 0000000000000246 R08: 0000000000000001 R09: 0000000000000000 [ 20.996576] R10: 0000000000000001 R11: 000000000000021c R12: 0000000000000246 [ 20.996576] R13: ffff8b1881363958 R14: 0000000000000000 R15: ffff8b1881363800 [ 20.996576] ? _raw_spin_unlock_irqrestore+0x4b/0x70 [ 20.996576] serial_port_runtime_resume+0xd4/0x1a0 [ 20.996576] ? __pfx_serial_port_runtime_resume+0x10/0x10 [ 20.996576] __rpm_callback+0x44/0x170 [ 20.996576] ? __pfx_serial_port_runtime_resume+0x10/0x10 [ 20.996576] rpm_callback+0x55/0x60 [ 20.996576] ? __pfx_serial_port_runtime_resume+0x10/0x10 [ 20.996576] rpm_resume+0x582/0x7b0 [ 20.996576] pm_runtime_work+0x7c/0xb0 [ 20.996576] process_one_work+0x1fb/0x590 [ 20.996576] worker_thread+0x18e/0x350 [ 20.996576] ? __pfx_worker_thread+0x10/0x10 [ 20.996576] kthread+0xe2/0x110 [ 20.996576] ? __pfx_kthread+0x10/0x10 [ 20.996576] ret_from_fork+0x34/0x50 [ 20.996576] ? __pfx_kthread+0x10/0x10 [ 20.996576] ret_from_fork_asm+0x1a/0x30 [ 20.996576] </TASK> [ 21.056592] sched_ext: BPF scheduler "simple" disabled (unregistered from user space) Signed-off-by: Changwoo Min <changwoo@igalia.com> Acked-by: Andrea Righi <arighi@nvidia.com> Signed-off-by: Tejun Heo <tj@kernel.org>
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.