>> + /* >> + * Ensure that the page's data was copied from old one by >> + * aio_migratepage(). >> + */ >> + smp_rmb(); >> + > > smp_read_barrier_depends() is better. > > "One could place an A smp_rmb() primitive between the pointer fetch and > dereference. However, this imposes unneeded overhead on systems (such as > i386, IA64, PPC, and SPARC) that respect data dependencies on the read side. > A smp_read_barrier_depends() primitive has been added to the Linux 2.6 kernel > to eliminate overhead on these systems." > -- From Chapter 7.1 of <Memory Barriers: a Hardware View for > Software Hackers> > Written by Paul E. McKenney >
Right. The document of memory barrier described this situation. see https://www.kernel.org/doc/Documentation/memory-barriers.txt CPU 1 CPU 2 =============== =============== { M[0] == 1, M[1] == 2, M[3] = 3, P == 0, Q == 3 } M[1] = 4; <write barrier> ACCESS_ONCE(P) = 1 Q = ACCESS_ONCE(P); <data dependency barrier> D = M[Q]; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
