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SubjectRe: [RFC PATCH] kprobes: Use synchronize_rcu_tasks_rude in kprobe_optimizer
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Hello,

PING.

I had a similar problem. Is this solution feasible?

Thanks,
Yang

On 2024/1/2 11:40, Chen Zhongjin 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@huawei.com>
> ---
> arch/Kconfig | 2 +-
> kernel/kprobes.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index f4b210ab0612..dc6a18854017 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -104,7 +104,7 @@ config STATIC_CALL_SELFTEST
> config OPTPROBES
> def_bool y
> depends on KPROBES && HAVE_OPTPROBES
> - select TASKS_RCU if PREEMPTION
> + select TASKS_RUDE_RCU
>
> config KPROBES_ON_FTRACE
> def_bool y
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index d5a0ee40bf66..09056ae50c58 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -623,7 +623,7 @@ static void kprobe_optimizer(struct work_struct *work)
> * Note that on non-preemptive kernel, this is transparently converted
> * to synchronoze_sched() to wait for all interrupts to have completed.
> */
> - synchronize_rcu_tasks();
> + synchronize_rcu_tasks_rude();
>
> /* Step 3: Optimize kprobes after quiesence period */
> do_optimize_kprobes();
>

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