[POWERPC] spufs: reacquire LS pointer in spu_process_callback

During spu_process callback, we release then acquire the SPU, but keep a
pointer to the local store memory. Since the context may have been
scheduled out during the callback, the ls pointer may become invalid.

This change reacquires the pointer to the context local store after
spu_acquire()-ing, so that it isn't invalidated by a context switch.
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

arch/powerpc/platforms/cell/spufs/run.c

@@ -323,6 +323,10 @@ static int spu_process_callback(struct spu_context *ctx)
 			return -EINTR;
 	}
 
+	/* need to re-get the ls, as it may have changed when we released the
+	 * spu */
+	ls = (void __iomem *)ctx->ops->get_ls(ctx);
+
 	/* write result, jump over indirect pointer */
 	memcpy_toio(ls + ls_pointer, &spu_ret, sizeof(spu_ret));
 	ctx->ops->npc_write(ctx, npc);