From: "Paul E. McKenney" Subject: [PATCH] vfs: fix RCU-lockdep false positive due to /proc access Date: Tue, 11 May 2010 10:23:56 -0700 Message-ID: <20100511172356.GA11103@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: viro@zeniv.linux.org.uk, mingo@elte.hu, miles.lane@gmail.com, eric.dumazet@gmail.com To: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Return-path: Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org 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 --- 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))