path: root/kernel/rcu/update.c
diff options
authorOleg Nesterov <>2014-01-11 19:19:32 +0100
committerAl Viro <>2014-01-25 03:14:36 -0500
commita8d4b8345e0ee48b732126d980efaf0dc373e2b0 (patch)
tree4bdfc52ef4ad176f54e4ce7b81091c0fbef0fd04 /kernel/rcu/update.c
parent2ccdc413196b43a02bb68b46be5b68850904e9ea (diff)
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 <>
Diffstat (limited to 'kernel/rcu/update.c')
1 files changed, 0 insertions, 11 deletions
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 6cb3dff89e2b..a3596c8ec9e4 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -195,17 +195,6 @@ void wait_rcu_gp(call_rcu_func_t crf)
- * wrapper function to avoid #include problems.
- */
-int rcu_my_thread_group_empty(void)
- return thread_group_empty(current);
-#endif /* #ifdef CONFIG_PROVE_RCU */
static inline void debug_init_rcu_head(struct rcu_head *head)