[PATCH 3/5] fork: Remove assumption that vm_area->nr_pages equals to THREAD_SIZE

[Linus Walleij <linus.walleij@linaro.org>]

From: Pasha Tatashin <pasha.tatashin@soleen.com>

In many places number of pages in the stack is detremined via
(THREAD_SIZE / PAGE_SIZE). There is also a BUG_ON() that ensures that
(THREAD_SIZE / PAGE_SIZE) is indeed equal to vm_area->nr_pages.

Consistently use vm_area->nr_pages to determine the actual number
of pages allocated in the stack instead, so it is clear what is
going on here.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Link: https://lore.kernel.org/20240311164638.2015063-5-pasha.tatashin@soleen.com
[Rebased, also skipped intermediary helper variable nr_pages]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 kernel/fork.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 3bed36a56292e3b868895dac169266c428f8c1ff..02943c14ee3b932db11cd9292051fdf5ce381a38 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -254,9 +254,7 @@ static int memcg_charge_kernel_stack(struct vm_struct *vm_area)
 	int ret;
 	int nr_charged = 0;
 
-	BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
-
-	for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
+	for (i = 0; i < vm_area->nr_pages; i++) {
 		ret = memcg_kmem_charge_page(vm_area->pages[i], GFP_KERNEL, 0);
 		if (ret)
 			goto err;
@@ -518,7 +516,7 @@ static void account_kernel_stack(struct task_struct *tsk, int account)
 		struct vm_struct *vm_area = task_stack_vm_area(tsk);
 		int i;
 
-		for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++)
+		for (i = 0; i < vm_area->nr_pages; i++)
 			mod_lruvec_page_state(vm_area->pages[i], NR_KERNEL_STACK_KB,
 					      account * (PAGE_SIZE / 1024));
 	} else {
@@ -539,7 +537,7 @@ void exit_task_stack_account(struct task_struct *tsk)
 		int i;
 
 		vm_area = task_stack_vm_area(tsk);
-		for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++)
+		for (i = 0; i < vm_area->nr_pages; i++)
 			memcg_kmem_uncharge_page(vm_area->pages[i], 0);
 	}
 }

-- 
2.49.0