From a8d4b8345e0ee48b732126d980efaf0dc373e2b0 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Sat, 11 Jan 2014 19:19:32 +0100 Subject: introduce __fcheck_files() to fix rcu_dereference_check_fdtable(), kill rcu_my_thread_group_empty() rcu_dereference_check_fdtable() looks very wrong, 1. rcu_my_thread_group_empty() was added by 844b9a8707f1 "vfs: fix RCU-lockdep false positive due to /proc" but it doesn't really fix the problem. A CLONE_THREAD (without CLONE_FILES) task can hit the same race with get_files_struct(). And otoh rcu_my_thread_group_empty() can suppress the correct warning if the caller is the CLONE_FILES (without CLONE_THREAD) task. 2. files->count == 1 check is not really right too. Even if this files_struct is not shared it is not safe to access it lockless unless the caller is the owner. Otoh, this check is sub-optimal. files->count == 0 always means it is safe to use it lockless even if files != current->files, but put_files_struct() has to take rcu_read_lock(). See the next patch. This patch removes the buggy checks and turns fcheck_files() into __fcheck_files() which uses rcu_dereference_raw(), the "unshared" callers, fget_light() and fget_raw_light(), can use it to avoid the warning from RCU-lockdep. fcheck_files() is trivially reimplemented as rcu_lockdep_assert() plus __fcheck_files(). Signed-off-by: Oleg Nesterov Signed-off-by: Al Viro --- include/linux/rcupdate.h | 2 -- 1 file changed, 2 deletions(-) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 39cbb889e20d..a2482cf90b6b 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -448,8 +448,6 @@ static inline int rcu_read_lock_sched_held(void) #ifdef CONFIG_PROVE_RCU -extern int rcu_my_thread_group_empty(void); - /** * rcu_lockdep_assert - emit lockdep splat if specified condition not met * @c: condition to check -- cgit