[PATCH] kprobes: Use synchronize_rcu_tasks_rude in kprobe_optimizer

[Chen Zhongjin]

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 <chenzhong...@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