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Subject[RFC PATCH] kprobes: Use synchronize_rcu_tasks_rude in kprobe_optimizer
Date
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();
--
2.25.1

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