From 844b9a8707f1fcf0482e0c52f44a555e799ccda6 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 20 Jul 2010 13:24:34 -0700 Subject: [PATCH] vfs: fix RCU-lockdep false positive due to /proc If a single-threaded process does a file-descriptor operation, and some other process accesses that same file descriptor via /proc, the current rcu_dereference_check_fdtable() can give a false-positive RCU-lockdep splat due to the reference count being increased by the /proc access after the reference-count check in fget_light() but before the check in rcu_dereference_check_fdtable(). This commit prevents this false positive by checking for a single-threaded process. To avoid #include hell, this commit uses the wrapper for thread_group_empty(current) defined by rcu_my_thread_group_empty() provided in a separate commit. Located-by: Miles Lane Located-by: Eric Dumazet Signed-off-by: Paul E. McKenney Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/fdtable.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h index 013dc529e95f..d147461bc271 100644 --- a/include/linux/fdtable.h +++ b/include/linux/fdtable.h @@ -61,7 +61,8 @@ struct files_struct { (rcu_dereference_check((fdtfd), \ rcu_read_lock_held() || \ lockdep_is_held(&(files)->file_lock) || \ - atomic_read(&(files)->count) == 1)) + atomic_read(&(files)->count) == 1 || \ + rcu_my_thread_group_empty())) #define files_fdtable(files) \ (rcu_dereference_check_fdtable((files), (files)->fdt)) -- 2.20.1