Messages in this thread Patch in this message | | | Date | Thu, 24 Jun 2010 12:14:01 -0700 | From | "Paul E. McKenney" <> | Subject | [PATCH] vfs rerepost: 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 <miles.lane@gmail.com> Located-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Al Viro <viro@ZenIV.linux.org.uk> --- fdtable.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h index 013dc52..d147461 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))
| |