commit 3b885ac1dc35b87a39ee176a6c7e2af9c789d8b8 upstream.
Now that mb() is an instruction barrier, it will slow performance if we issue
unnecessary barriers.
The spinlock defines have a number of unnecessary barriers. The __ldcw()
define is both a hardware and compiler barrier. The mb() barriers in the
routines using __ldcw() serve no purpose.
The only barrier needed is the one in arch_spin_unlock(). We need to ensure
all accesses are complete prior to releasing the lock.
Signed-off-by: John David Anglin <dave.anglin@bell.net>
Cc: stable@vger.kernel.org # 4.0+
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
400db6fe74