percpu: more flexibility for @dyn_size of pcpu_setup_first_chunk()

Impact: cleanup, more flexibility for first chunk init

Non-negative @dyn_size used to be allowed iff @unit_size wasn't auto.
This restriction stemmed from implementation detail and made things a
bit less intuitive.  This patch allows @dyn_size to be specified
regardless of @unit_size and swaps the positions of @dyn_size and
@unit_size so that the parameter order makes more sense (static,
reserved and dyn sizes followed by enclosing unit_size).

While at it, add @unit_size >= PCPU_MIN_UNIT_SIZE sanity check.

Signed-off-by: Tejun Heo <tj@kernel.org>

3 files changed, 21 insertions, 22 deletions

diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index efa615f2bf43..e41c51f6ada1 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -233,8 +233,8 @@ proceed:
                 "%zu bytes\n", vm.addr, static_size);
 
         ret = pcpu_setup_first_chunk(pcpur_get_page, static_size,
-                                     PERCPU_FIRST_CHUNK_RESERVE,
-                                     PMD_SIZE, dyn_size, vm.addr, NULL);
+                                     PERCPU_FIRST_CHUNK_RESERVE, dyn_size,
+                                     PMD_SIZE, vm.addr, NULL);
         goto out_free_ar;
 
 enomem:
@@ -315,9 +315,8 @@ static ssize_t __init setup_pcpu_embed(size_t static_size)
                 pcpue_size >> PAGE_SHIFT, pcpue_ptr, static_size);
 
         return pcpu_setup_first_chunk(pcpue_get_page, static_size,
-                                      PERCPU_FIRST_CHUNK_RESERVE,
-                                      pcpue_unit_size, dyn_size,
-                                      pcpue_ptr, NULL);
+                                      PERCPU_FIRST_CHUNK_RESERVE, dyn_size,
+                                      pcpue_unit_size, pcpue_ptr, NULL);
 }
 
 /*
@@ -375,8 +374,8 @@ static ssize_t __init setup_pcpu_4k(size_t static_size)
                 pcpu4k_nr_static_pages, static_size);
 
         ret = pcpu_setup_first_chunk(pcpu4k_get_page, static_size,
-                                     PERCPU_FIRST_CHUNK_RESERVE, -1, -1, NULL,
-                                     pcpu4k_populate_pte);
+                                     PERCPU_FIRST_CHUNK_RESERVE, -1,
+                                     -1, NULL, pcpu4k_populate_pte);
         goto out_free_ar;
 
 enomem:
diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index 54a968b4b924..fb455dcc59c7 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -107,7 +107,7 @@ typedef void (*pcpu_populate_pte_fn_t)(unsigned long addr);
 
 extern size_t __init pcpu_setup_first_chunk(pcpu_get_page_fn_t get_page_fn,
                                 size_t static_size, size_t reserved_size,
-                                ssize_t unit_size, ssize_t dyn_size,
+                                ssize_t dyn_size, ssize_t unit_size,
                                 void *base_addr,
                                 pcpu_populate_pte_fn_t populate_pte_fn);
 
diff --git a/mm/percpu.c b/mm/percpu.c
index c6f38a2aface..2f94661d3e36 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1027,8 +1027,8 @@ EXPORT_SYMBOL_GPL(free_percpu);
  * @get_page_fn: callback to fetch page pointer
  * @static_size: the size of static percpu area in bytes
  * @reserved_size: the size of reserved percpu area in bytes
- * @unit_size: unit size in bytes, must be multiple of PAGE_SIZE, -1 for auto
  * @dyn_size: free size for dynamic allocation in bytes, -1 for auto
+ * @unit_size: unit size in bytes, must be multiple of PAGE_SIZE, -1 for auto
  * @base_addr: mapped address, NULL for auto
  * @populate_pte_fn: callback to allocate pagetable, NULL if unnecessary
  *
@@ -1053,14 +1053,14 @@ EXPORT_SYMBOL_GPL(free_percpu);
  * limited offset range for symbol relocations to guarantee module
  * percpu symbols fall inside the relocatable range.
  *
+ * @dyn_size, if non-negative, determines the number of bytes
+ * available for dynamic allocation in the first chunk.  Specifying
+ * non-negative value makes percpu leave alone the area beyond
+ * @static_size + @reserved_size + @dyn_size.
+ *
  * @unit_size, if non-negative, specifies unit size and must be
  * aligned to PAGE_SIZE and equal to or larger than @static_size +
- * @reserved_size + @dyn_size.
- *
- * @dyn_size, if non-negative, limits the number of bytes available
- * for dynamic allocation in the first chunk.  Specifying non-negative
- * value make percpu leave alone the area beyond @static_size +
- * @reserved_size + @dyn_size.
+ * @reserved_size + if non-negative, @dyn_size.
  *
  * Non-null @base_addr means that the caller already allocated virtual
  * region for the first chunk and mapped it.  percpu must not mess
@@ -1083,12 +1083,14 @@ EXPORT_SYMBOL_GPL(free_percpu);
  */
 size_t __init pcpu_setup_first_chunk(pcpu_get_page_fn_t get_page_fn,
                                      size_t static_size, size_t reserved_size,
-                                     ssize_t unit_size, ssize_t dyn_size,
+                                     ssize_t dyn_size, ssize_t unit_size,
                                      void *base_addr,
                                      pcpu_populate_pte_fn_t populate_pte_fn)
 {
         static struct vm_struct first_vm;
         static int smap[2], dmap[2];
+        size_t size_sum = static_size + reserved_size +
+                          (dyn_size >= 0 ? dyn_size : 0);
         struct pcpu_chunk *schunk, *dchunk = NULL;
         unsigned int cpu;
         int nr_pages;
@@ -1099,20 +1101,18 @@ size_t __init pcpu_setup_first_chunk(pcpu_get_page_fn_t get_page_fn,
                      ARRAY_SIZE(dmap) >= PCPU_DFL_MAP_ALLOC);
         BUG_ON(!static_size);
         if (unit_size >= 0) {
-                BUG_ON(unit_size < static_size + reserved_size +
-                                   (dyn_size >= 0 ? dyn_size : 0));
+                BUG_ON(unit_size < size_sum);
                 BUG_ON(unit_size & ~PAGE_MASK);
-        } else {
-                BUG_ON(dyn_size >= 0);
+                BUG_ON(unit_size < PCPU_MIN_UNIT_SIZE);
+        } else
                 BUG_ON(base_addr);
-        }
         BUG_ON(base_addr && populate_pte_fn);
 
         if (unit_size >= 0)
                 pcpu_unit_pages = unit_size >> PAGE_SHIFT;
         else
                 pcpu_unit_pages = max_t(int, PCPU_MIN_UNIT_SIZE >> PAGE_SHIFT,
-                                        PFN_UP(static_size + reserved_size));
+                                        PFN_UP(size_sum));
 
         pcpu_unit_size = pcpu_unit_pages << PAGE_SHIFT;
         pcpu_chunk_size = num_possible_cpus() * pcpu_unit_size;