Re: [PATCH] kprobes: Use synchronize_rcu_tasks_rude in kprobe_optimizer

[Andrew Morton]

On Wed, 17 Jan 2024 06:16:36 +0000 Chen Zhongjin <chenzhongjin@xxxxxxxxxx> wrote:

> There is a deadlock scenario in kprobe_optimizer():
> 
> pid A				pid B			pid C
> kprobe_optimizer()		do_exit()		perf_kprobe_init()
> mutex_lock(&kprobe_mutex)	exit_tasks_rcu_start()	mutex_lock(&kprobe_mutex)
> synchronize_rcu_tasks()		zap_pid_ns_processes()	// waiting kprobe_mutex
> // waiting tasks_rcu_exit_srcu	kernel_wait4()
> 				// waiting pid C exit
> 
> To avoid this deadlock loop, use synchronize_rcu_tasks_rude() in kprobe_optimizer()
> rather than synchronize_rcu_tasks(). synchronize_rcu_tasks_rude() can also promise
> that all preempted tasks have scheduled, but it will not wait tasks_rcu_exit_srcu.
> 
> Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>

Thanks.  Should we backport this fix into earlier kernels?  If so, are
we able to identify a suitable Fixes: target?