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 (file)
--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -146,7 +146,7 @@ compat_sys_get_robust_list(int pid, compat_uptr_t __user *head_ptr,
                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 @@ compat_sys_get_robust_list(int pid, compat_uptr_t __user *head_ptr,
                    !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 @@ compat_sys_get_robust_list(int pid, compat_uptr_t __user *head_ptr,
        return put_user(ptr_to_compat(head), head_ptr);
 
 err_unlock:
-       read_unlock(&tasklist_lock);
+       rcu_read_unlock();
 
        return ret;
 }