• Oleg Nesterov's avatar
    introduce __fcheck_files() to fix rcu_dereference_check_fdtable(), kill rcu_my_thread_group_empty() · a8d4b834
    Oleg Nesterov authored
    rcu_dereference_check_fdtable() looks very wrong,
    
    1. rcu_my_thread_group_empty() was added by 844b9a87 "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: default avatarOleg Nesterov <oleg@redhat.com>
    Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
    a8d4b834
update.c 9.97 KB