[PATCH v2 2/6] mm/vmalloc: set area's page_order after allocation succeeds

[Mike Rapoport (Microsoft)]

__vmalloc_area_node() calls set_vm_area_page_order() to set area's
page_order before actually allocating pages to populate the area.

If allocation of large pages in HUGE_VMAP case fails midway, this leaves
the area with elevated page_order throughout the cleanup path.

There is no actual issue with this because the only place that currently
relies on area->page_order on the cleanup path is the loop calculating
the direct map alias range in vm_reset_perms() and it anyway skips
unpopulated pages.

But having set_vm_area_page_order() in the middle of __vmalloc_area_node()
makes things very obscure, hard to reason about and error prone against
future changes of the cleanup path.

Move the call to set_vm_area_page_order() just before the successful
return from __vmalloc_area_node() where page order is guaranteed.

While on it, initialize local page_order variable with its declaration.

Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
---
 mm/vmalloc.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 22566e0b6e38..9bd94e2f2895 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3873,7 +3873,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 	unsigned long size = get_vm_area_size(area);
 	unsigned long array_size;
 	unsigned long nr_small_pages = size >> PAGE_SHIFT;
-	unsigned int page_order;
+	unsigned int page_order = page_shift - PAGE_SHIFT;
 	unsigned int flags;
 	int ret;
 
@@ -3901,9 +3901,6 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 		goto fail;
 	}
 
-	set_vm_area_page_order(area, page_shift - PAGE_SHIFT);
-	page_order = vm_area_page_order(area);
-
 	/*
 	 * High-order nofail allocations are really expensive and
 	 * potentially dangerous (pre-mature OOM, disruptive reclaim
@@ -3958,6 +3955,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 		goto fail;
 	}
 
+	set_vm_area_page_order(area, page_order);
 	return area->addr;
 
 fail:

-- 
2.53.0