futex: Protect pid lookup in compat code with RCU
find_task_by_vpid() in compat_sys_get_robust_list() does not require
tasklist_lock. It can be protected with rcu_read_lock as done in
sys_get_robust_list() already.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Darren Hart <dvhltc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c
index 2357165..d49afb2 100644
--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -146,7 +146,7 @@
struct task_struct *p;
ret = -ESRCH;
- read_lock(&tasklist_lock);
+ rcu_read_lock();
p = find_task_by_vpid(pid);
if (!p)
goto err_unlock;
@@ -157,7 +157,7 @@
!capable(CAP_SYS_PTRACE))
goto err_unlock;
head = p->compat_robust_list;
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
}
if (put_user(sizeof(*head), len_ptr))
@@ -165,7 +165,7 @@
return put_user(ptr_to_compat(head), head_ptr);
err_unlock:
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
return ret;
}