* [linux-next:master 4756/5283] kernel/fork.c:457 account_kernel_stack() warn: we never enter this loop
@ 2025-09-01 10:56 Dan Carpenter
2025-09-02 17:01 ` Vishal Moola (Oracle)
0 siblings, 1 reply; 2+ messages in thread
From: Dan Carpenter @ 2025-09-01 10:56 UTC (permalink / raw)
To: oe-kbuild, Vishal Moola (Oracle)
Cc: lkp, oe-kbuild-all, Andrew Morton, Linux Memory Management List
tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head: 3cace99d63192a7250461b058279a42d91075d0c
commit: e0aa7237ef4323a66ed06953225d9b07cf039530 [4756/5283] mm: tag kernel stack pages
config: hexagon-randconfig-r072-20250829 (https://download.01.org/0day-ci/archive/20250830/202508300929.TrRovUMu-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
| Closes: https://lore.kernel.org/r/202508300929.TrRovUMu-lkp@intel.com/
smatch warnings:
kernel/fork.c:457 account_kernel_stack() warn: we never enter this loop
kernel/fork.c:457 account_kernel_stack() warn: unsigned 'i' is never less than zero.
kernel/fork.c:479 exit_task_stack_account() warn: we never enter this loop
kernel/fork.c:479 exit_task_stack_account() warn: unsigned 'i' is never less than zero.
vim +457 kernel/fork.c
ba14a194a434cc Andy Lutomirski 2016-08-11 437 static void account_kernel_stack(struct task_struct *tsk, int account)
c6a7f5728a1db4 KOSAKI Motohiro 2009-09-21 438 {
0ce055f85335e4 Sebastian Andrzej Siewior 2022-02-17 439 if (IS_ENABLED(CONFIG_VMAP_STACK)) {
449e0b4ed5a16c Pasha Tatashin 2025-05-09 440 struct vm_struct *vm_area = task_stack_vm_area(tsk);
27faca83a7e955 Muchun Song 2021-04-29 441 int i;
efdc94907977d2 Andy Lutomirski 2016-07-28 442
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 443) for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
449e0b4ed5a16c Pasha Tatashin 2025-05-09 444 mod_lruvec_page_state(vm_area->pages[i], NR_KERNEL_STACK_KB,
27faca83a7e955 Muchun Song 2021-04-29 445 account * (PAGE_SIZE / 1024));
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 446) __SetPageStack(vm_area->pages[i]);
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 447) }
27faca83a7e955 Muchun Song 2021-04-29 448 } else {
0ce055f85335e4 Sebastian Andrzej Siewior 2022-02-17 449 void *stack = task_stack_page(tsk);
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 450) struct page *page = virt_to_head_page(stack);
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 451) int i;
0ce055f85335e4 Sebastian Andrzej Siewior 2022-02-17 452
991e7673859ed4 Shakeel Butt 2020-08-06 453 /* All stack pages are in the same node. */
da3ceeff923e3b Muchun Song 2020-12-14 454 mod_lruvec_kmem_state(stack, NR_KERNEL_STACK_KB,
efdc94907977d2 Andy Lutomirski 2016-07-28 455 account * (THREAD_SIZE / 1024));
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 456)
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 @457) for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++, page++)
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 458) __SetPageStack(page);
Apparently in the linked config the THREAD_SIZE / PAGE_SIZE is zero.
Is this the expected behavior? I don't know mm enough to say the
answer...
ba14a194a434cc Andy Lutomirski 2016-08-11 459 }
27faca83a7e955 Muchun Song 2021-04-29 460 }
c6a7f5728a1db4 KOSAKI Motohiro 2009-09-21 461
1a03d3f13ffe5d Sebastian Andrzej Siewior 2022-02-17 462 void exit_task_stack_account(struct task_struct *tsk)
9b6f7e163cd0f4 Roman Gushchin 2018-10-26 463 {
1a03d3f13ffe5d Sebastian Andrzej Siewior 2022-02-17 464 account_kernel_stack(tsk, -1);
991e7673859ed4 Shakeel Butt 2020-08-06 465
1a03d3f13ffe5d Sebastian Andrzej Siewior 2022-02-17 466 if (IS_ENABLED(CONFIG_VMAP_STACK)) {
449e0b4ed5a16c Pasha Tatashin 2025-05-09 467 struct vm_struct *vm_area;
9b6f7e163cd0f4 Roman Gushchin 2018-10-26 468 int i;
9b6f7e163cd0f4 Roman Gushchin 2018-10-26 469
449e0b4ed5a16c Pasha Tatashin 2025-05-09 470 vm_area = task_stack_vm_area(tsk);
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 471) for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
449e0b4ed5a16c Pasha Tatashin 2025-05-09 472 memcg_kmem_uncharge_page(vm_area->pages[i], 0);
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 473) __ClearPageStack(vm_area->pages[i]);
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 474) }
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 475) } else {
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 476) struct page *page = virt_to_head_page(task_stack_page(tsk));
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 477) int i;
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 478)
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 @479) for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++, page++)
e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 480) __ClearPageStack(page);
9b6f7e163cd0f4 Roman Gushchin 2018-10-26 481 }
9b6f7e163cd0f4 Roman Gushchin 2018-10-26 482 }
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [linux-next:master 4756/5283] kernel/fork.c:457 account_kernel_stack() warn: we never enter this loop
2025-09-01 10:56 [linux-next:master 4756/5283] kernel/fork.c:457 account_kernel_stack() warn: we never enter this loop Dan Carpenter
@ 2025-09-02 17:01 ` Vishal Moola (Oracle)
0 siblings, 0 replies; 2+ messages in thread
From: Vishal Moola (Oracle) @ 2025-09-02 17:01 UTC (permalink / raw)
To: Dan Carpenter
Cc: oe-kbuild, lkp, oe-kbuild-all, Andrew Morton,
Linux Memory Management List
On Mon, Sep 01, 2025 at 01:56:05PM +0300, Dan Carpenter wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head: 3cace99d63192a7250461b058279a42d91075d0c
> commit: e0aa7237ef4323a66ed06953225d9b07cf039530 [4756/5283] mm: tag kernel stack pages
> config: hexagon-randconfig-r072-20250829 (https://download.01.org/0day-ci/archive/20250830/202508300929.TrRovUMu-lkp@intel.com/config)
> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> | Closes: https://lore.kernel.org/r/202508300929.TrRovUMu-lkp@intel.com/
>
> smatch warnings:
> kernel/fork.c:457 account_kernel_stack() warn: we never enter this loop
> kernel/fork.c:457 account_kernel_stack() warn: unsigned 'i' is never less than zero.
> kernel/fork.c:479 exit_task_stack_account() warn: we never enter this loop
> kernel/fork.c:479 exit_task_stack_account() warn: unsigned 'i' is never less than zero.
Thanks for catching this!
> vim +457 kernel/fork.c
>
> ba14a194a434cc Andy Lutomirski 2016-08-11 437 static void account_kernel_stack(struct task_struct *tsk, int account)
> c6a7f5728a1db4 KOSAKI Motohiro 2009-09-21 438 {
> 0ce055f85335e4 Sebastian Andrzej Siewior 2022-02-17 439 if (IS_ENABLED(CONFIG_VMAP_STACK)) {
> 449e0b4ed5a16c Pasha Tatashin 2025-05-09 440 struct vm_struct *vm_area = task_stack_vm_area(tsk);
> 27faca83a7e955 Muchun Song 2021-04-29 441 int i;
> efdc94907977d2 Andy Lutomirski 2016-07-28 442
> e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 443) for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
> 449e0b4ed5a16c Pasha Tatashin 2025-05-09 444 mod_lruvec_page_state(vm_area->pages[i], NR_KERNEL_STACK_KB,
> 27faca83a7e955 Muchun Song 2021-04-29 445 account * (PAGE_SIZE / 1024));
> e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 446) __SetPageStack(vm_area->pages[i]);
> e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 447) }
> 27faca83a7e955 Muchun Song 2021-04-29 448 } else {
> 0ce055f85335e4 Sebastian Andrzej Siewior 2022-02-17 449 void *stack = task_stack_page(tsk);
> e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 450) struct page *page = virt_to_head_page(stack);
> e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 451) int i;
> 0ce055f85335e4 Sebastian Andrzej Siewior 2022-02-17 452
> 991e7673859ed4 Shakeel Butt 2020-08-06 453 /* All stack pages are in the same node. */
> da3ceeff923e3b Muchun Song 2020-12-14 454 mod_lruvec_kmem_state(stack, NR_KERNEL_STACK_KB,
> efdc94907977d2 Andy Lutomirski 2016-07-28 455 account * (THREAD_SIZE / 1024));
> e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 456)
> e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 @457) for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++, page++)
> e0aa7237ef4323 Vishal Moola (Oracle 2025-08-20 458) __SetPageStack(page);
>
> Apparently in the linked config the THREAD_SIZE / PAGE_SIZE is zero.
> Is this the expected behavior? I don't know mm enough to say the
> answer...
THREAD_SIZE and PAGE_SIZE are very architecture dependent. This behavior
is expected in some configs. This can't happen in the VMAP_STACK case,
only !VMAP_STACK, so looks like my patch is wrong in handling that case.
I'll send a fix shortly.
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