[[PATCH v2] 1/2] futex: Add check_robust_futex to verify process usage of robust_futex

[<zhongjinji@honor.com>]

From: zhongjinji <zhongjinji@honor.com>

The check_robust_futex function is added to detect whether a process uses
robust_futex.

According to the patch discussion
(https://lore.kernel.org/all/20220414144042.677008-1-npache@redhat.com/T/#u),
executing the OOM reaper too early on processes using robust_futex may cause
the lock holder to wait indefinitely.

Therefore, this patch introduces check_robust_futex to identify such
processes during OOM reaper execution, and delays the OOM reaper specifically
for processes using robust_futex.

Signed-off-by: zhongjinji <zhongjinji@honor.com>
---
 include/linux/futex.h | 11 ++++++++++-
 kernel/futex/core.c   | 25 +++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/include/linux/futex.h b/include/linux/futex.h
index 9e9750f04980..b3ce7424609d 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -81,7 +81,8 @@ void futex_exec_release(struct task_struct *tsk);
 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
 	      u32 __user *uaddr2, u32 val2, u32 val3);
 int futex_hash_prctl(unsigned long arg2, unsigned long arg3, unsigned long arg4);
-
+bool check_robust_futex(struct task_struct *p);
+bool __check_robust_futex(struct task_struct *p);
 #ifdef CONFIG_FUTEX_PRIVATE_HASH
 int futex_hash_allocate_default(void);
 void futex_hash_free(struct mm_struct *mm);
@@ -108,6 +109,14 @@ static inline int futex_hash_prctl(unsigned long arg2, unsigned long arg3, unsig
 {
 	return -EINVAL;
 }
+static inline bool check_robust_futex(struct task_struct *p)
+{
+	return false;
+}
+static inline bool __check_robust_futex(struct task_struct *p)
+{
+	return false;
+}
 static inline int futex_hash_allocate_default(void)
 {
 	return 0;
diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index d9bb5567af0c..6cd385a62455 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -1513,6 +1513,31 @@ void futex_exit_release(struct task_struct *tsk)
 	futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
 }
 
+bool __check_robust_futex(struct task_struct *p)
+{
+	struct task_struct *t;
+
+	for_each_thread(p, t) {
+		if (unlikely(t->robust_list))
+			return true;
+#ifdef CONFIG_COMPAT
+		if (unlikely(t->compat_robust_list))
+			return true;
+#endif
+	}
+	return false;
+}
+
+bool check_robust_futex(struct task_struct *p)
+{
+	bool has_robust;
+
+	rcu_read_lock();
+	has_robust = __check_robust_futex(p);
+	rcu_read_unlock();
+	return has_robust;
+}
+
 static void futex_hash_bucket_init(struct futex_hash_bucket *fhb,
 				   struct futex_private_hash *fph)
 {
-- 
2.17.1