This is a note to let you know that I've just added the patch titled
sched_ext: add a missing rcu_read_lock/unlock pair at scx_select_cpu_dfl()
to the 6.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched_ext-add-a-missing-rcu_read_lock-unlock-pair-at.patch
and it can be found in the queue-6.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit a645f346c2beefb575749848f249566bb3850a31
Author: Changwoo Min <multics69@xxxxxxxxx>
Date: Sat Nov 9 15:29:05 2024 +0900
sched_ext: add a missing rcu_read_lock/unlock pair at scx_select_cpu_dfl()
[ Upstream commit f39489fea677ad78ca4ce1ab2d204a6639b868dc ]
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@xxxxxxxxxx>
Acked-by: Andrea Righi <arighi@xxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 16613631543f1..79bb18651cdb8 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3105,6 +3105,12 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
*found = false;
+
+ /*
+ * This is necessary to protect llc_cpus.
+ */
+ rcu_read_lock();
+
/*
* If WAKE_SYNC, the waker's local DSQ is empty, and the system is
* under utilized, wake up @p to the local DSQ of the waker. Checking
@@ -3147,9 +3153,12 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
if (cpu >= 0)
goto cpu_found;
+ rcu_read_unlock();
return prev_cpu;
cpu_found:
+ rcu_read_unlock();
+
*found = true;
return cpu;
}
