Commit 844b9a87 authored Jul 20, 2010 by Paul E. McKenney Committed by Linus Torvalds Jul 20, 2010

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 <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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 9d51a6b2

include/linux/fdtable.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -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))

Admin message