On Thu, 18 Jan 2024 02:18:42 +0000
Chen Zhongjin <chenzhong...@huawei.com> 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.
>
Did lockdep detect this? If not, we should fix that.
I'm also thinking if we should find another solution, as this seems more of
a work around than a fix.
> Fixes: a30b85df7d59 ("kprobes: Use synchronize_rcu_tasks() for optprobe with
> CONFIG_PREEMPT=y")
> Signed-off-by: Chen Zhongjin <chenzhong...@huawei.com>
> ---
> v1 -> v2: Add Fixes tag
> ---
> 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
Is this still a bug if PREEMPTION is not enabled?
-- Steve
>
> 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();
