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Commit 844b9a87 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Linus Torvalds
Browse files

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: default avatarMiles Lane <miles.lane@gmail.com>
Located-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus 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))