percpu: explain why per_cpu_ptr_to_phys() is more complicated than necessary

Add comments about current per_cpu_ptr_to_phys implementation to explain why the logic is more complicated than necessary. -tj: relocated comment into kerneldoc comment Signed-off-by: Dave Young <dyoung@redhat.com> Signed-off-by: Tejun Heo <tj@kernel.org>

percpu: explain why per_cpu_ptr_to_phys() is more complicated than necessary
Add comments about current per_cpu_ptr_to_phys implementation to explain why the logic is more complicated than necessary. -tj: relocated comment into kerneldoc comment Signed-off-by: Dave Young <dyoung@redhat.com> Signed-off-by: Tejun Heo <tj@kernel.org>
Dave Young · Tejun Heo
1 parent a855b84c3d
Showing 1 changed file with 11 additions and 0 deletions Side-by-side Diff
mm/percpu.c
@@ -978,6 +978,17 @@
  * address.  The caller is responsible for ensuring @addr stays valid
  * until this function finishes.
  *
+ * percpu allocator has special setup for the first chunk, which currently
+ * supports either embedding in linear address space or vmalloc mapping,
+ * and, from the second one, the backing allocator (currently either vm or
+ * km) provides translation.
+ *
+ * The addr can be tranlated simply without checking if it falls into the
+ * first chunk. But the current code reflects better how percpu allocator
+ * actually works, and the verification can discover both bugs in percpu
+ * allocator itself and per_cpu_ptr_to_phys() callers. So we keep current
+ * code.
+ *
  * RETURNS:
  * The physical address for @addr.
  */
...	...	@@ -978,6 +978,17 @@
978	978	* address. The caller is responsible for ensuring @addr stays valid
979	979	* until this function finishes.
980	980	*
	981	+ * percpu allocator has special setup for the first chunk, which currently
	982	+ * supports either embedding in linear address space or vmalloc mapping,
	983	+ * and, from the second one, the backing allocator (currently either vm or
	984	+ * km) provides translation.
	985	+ *
	986	+ * The addr can be tranlated simply without checking if it falls into the
	987	+ * first chunk. But the current code reflects better how percpu allocator
	988	+ * actually works, and the verification can discover both bugs in percpu
	989	+ * allocator itself and per_cpu_ptr_to_phys() callers. So we keep current
	990	+ * code.
	991	+ *
981	992	* RETURNS:
982	993	* The physical address for @addr.
983	994	*/