RISC-V: Provide a cleaner raw_smp_processor_id()

I'm not sure how I managed to miss this the first time, but this is much
better.
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
[Atish: code comment formatting and other fixes]
Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/include/asm/smp.h

@@ -14,13 +14,9 @@
 #ifndef _ASM_RISCV_SMP_H
 #define _ASM_RISCV_SMP_H
 
-/* This both needs asm-offsets.h and is used when generating it. */
-#ifndef GENERATING_ASM_OFFSETS
-#include <asm/asm-offsets.h>
-#endif
-
 #include <linux/cpumask.h>
 #include <linux/irqreturn.h>
+#include <linux/thread_info.h>
 
 #ifdef CONFIG_SMP
 
@@ -34,12 +30,10 @@ void arch_send_call_function_ipi_mask(struct cpumask *mask);
 void arch_send_call_function_single_ipi(int cpu);
 
 /*
- * This is particularly ugly: it appears we can't actually get the definition
- * of task_struct here, but we need access to the CPU this task is running on.
- * Instead of using C we're using asm-offsets.h to get the current processor
- * ID.
+ * Obtains the hart ID of the currently executing task.  This relies on
+ * THREAD_INFO_IN_TASK, but we define that unconditionally.
  */
-#define raw_smp_processor_id() (*((int*)((char*)get_current() + TASK_TI_CPU)))
+#define raw_smp_processor_id() (current_thread_info()->cpu)
 
 #endif /* CONFIG_SMP */