Re: [PATCH] codetag: debug: mark codetags for poisoned page as empty

[Hao Ge <hao.ge@linux.dev>]

Hi Suren


Thank you for reviewing this patch and for your suggestions.

The description looks clearer now. I will revise it based on your 
suggestions and send out version 2.


Best regards
Hao


On 8/24/24 00:39, Suren Baghdasaryan wrote:
> On Thu, Aug 22, 2024 at 11:21 PM Hao Ge <hao.ge@linux.dev> wrote:
>> From: Hao Ge <gehao@kylinos.cn>
>>
>> The PG_hwpoison page will be caught and isolated on the entrance to
>> the free buddy page pool.
>>
>> But for poisoned pages which software injected errors,
>> we can reclaim it through unpoison_memory.
>>
>> So mark codetags for it as empty,just like when a page
>> is first added to the buddy system.
>>
>> It was detected by [1] and the following WARN occurred:
> Hi Hao,
> Thanks for fixing this. I find this description a bit unclear. How
> about something like this:
>
> When PG_hwpoison pages are freed, they are treated differently in
> free_pages_prepare() and instead of being released they are isolated.
> Page allocation tag counters are decremented at this point since the
> page is considered not in use. Later on when such pages are released
> by unpoison_memory(), the allocation tag counters will be decremented
> again and the following warning gets reported:
>
>> [  113.930443][ T3282] ------------[ cut here ]------------
>> [  113.931105][ T3282] alloc_tag was not set
>> [  113.931576][ T3282] WARNING: CPU: 2 PID: 3282 at ./include/linux/alloc_tag.h:130 pgalloc_tag_sub.part.66+0x154/0x164
>> [  113.932866][ T3282] Modules linked in: hwpoison_inject fuse ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat ebtable_broute ip6table_nat ip6table_man4
>> [  113.941638][ T3282] CPU: 2 UID: 0 PID: 3282 Comm: madvise11 Kdump: loaded Tainted: G        W          6.11.0-rc4-dirty #18
>> [  113.943003][ T3282] Tainted: [W]=WARN
>> [  113.943453][ T3282] Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022
>> [  113.944378][ T3282] pstate: 40400005 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>> [  113.945319][ T3282] pc : pgalloc_tag_sub.part.66+0x154/0x164
>> [  113.946016][ T3282] lr : pgalloc_tag_sub.part.66+0x154/0x164
>> [  113.946706][ T3282] sp : ffff800087093a10
>> [  113.947197][ T3282] x29: ffff800087093a10 x28: ffff0000d7a9d400 x27: ffff80008249f0a0
>> [  113.948165][ T3282] x26: 0000000000000000 x25: ffff80008249f2b0 x24: 0000000000000000
>> [  113.949134][ T3282] x23: 0000000000000001 x22: 0000000000000001 x21: 0000000000000000
>> [  113.950597][ T3282] x20: ffff0000c08fcad8 x19: ffff80008251e000 x18: ffffffffffffffff
>> [  113.952207][ T3282] x17: 0000000000000000 x16: 0000000000000000 x15: ffff800081746210
>> [  113.953161][ T3282] x14: 0000000000000000 x13: 205d323832335420 x12: 5b5d353031313339
>> [  113.954120][ T3282] x11: ffff800087093500 x10: 000000000000005d x9 : 00000000ffffffd0
>> [  113.955078][ T3282] x8 : 7f7f7f7f7f7f7f7f x7 : ffff80008236ba90 x6 : c0000000ffff7fff
>> [  113.956036][ T3282] x5 : ffff000b34bf4dc8 x4 : ffff8000820aba90 x3 : 0000000000000001
>> [  113.956994][ T3282] x2 : ffff800ab320f000 x1 : 841d1e35ac932e00 x0 : 0000000000000000
>> [  113.957962][ T3282] Call trace:
>> [  113.958350][ T3282]  pgalloc_tag_sub.part.66+0x154/0x164
>> [  113.959000][ T3282]  pgalloc_tag_sub+0x14/0x1c
>> [  113.959539][ T3282]  free_unref_page+0xf4/0x4b8
>> [  113.960096][ T3282]  __folio_put+0xd4/0x120
>> [  113.960614][ T3282]  folio_put+0x24/0x50
>> [  113.961103][ T3282]  unpoison_memory+0x4f0/0x5b0
>> [  113.961678][ T3282]  hwpoison_unpoison+0x30/0x48 [hwpoison_inject]
>> [  113.962436][ T3282]  simple_attr_write_xsigned.isra.34+0xec/0x1cc
>> [  113.963183][ T3282]  simple_attr_write+0x38/0x48
>> [  113.963750][ T3282]  debugfs_attr_write+0x54/0x80
>> [  113.964330][ T3282]  full_proxy_write+0x68/0x98
>> [  113.964880][ T3282]  vfs_write+0xdc/0x4d0
>> [  113.965372][ T3282]  ksys_write+0x78/0x100
>> [  113.965875][ T3282]  __arm64_sys_write+0x24/0x30
>> [  113.966440][ T3282]  invoke_syscall+0x7c/0x104
>> [  113.966984][ T3282]  el0_svc_common.constprop.1+0x88/0x104
>> [  113.967652][ T3282]  do_el0_svc+0x2c/0x38
>> [  113.968893][ T3282]  el0_svc+0x3c/0x1b8
>> [  113.969379][ T3282]  el0t_64_sync_handler+0x98/0xbc
>> [  113.969980][ T3282]  el0t_64_sync+0x19c/0x1a0
>> [  113.970511][ T3282] ---[ end trace 0000000000000000 ]---
>>
>> Link [1]: https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/madvise/madvise11.c
> To fix this, clear the page tag reference after the page got isolated
> and accounted for.
>
>> Fixes: a8fc28dad6d5 ("alloc_tag: introduce clear_page_tag_ref() helper function")
> This would be more appropriate:
> Fixes: d224eb0287fb ("codetag: debug: mark codetags for reserved pages
> as empty")
>
>> Cc: stable@vger.kernel.org # v6.10
>> Signed-off-by: Hao Ge <gehao@kylinos.cn>
>> ---
>>   mm/page_alloc.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index c565de8f48e9..7ccd2157d092 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1054,6 +1054,14 @@ __always_inline bool free_pages_prepare(struct page *page,
>>                  reset_page_owner(page, order);
>>                  page_table_check_free(page, order);
>>                  pgalloc_tag_sub(page, 1 << order);
>> +
>> +               /*
>> +                * For poisoned pages which software injected errors,
> Not sure what you mean by "which software injected errors". Maybe it's
> a typo and should be "with software injected errors"?
>
>> +                * we can reclaim it through unpoison_memory.
>> +                * so mark codetags for it as empty,
>> +                * just like when a page is first added to the buddy system.
>> +                */
> I think you can simply say here that:
> /*
>   * The page is isolated and accounted for. Mark the codetag as empty to avoid
>   * accounting error when the page is freed by unpoison_memory().
>   */
>
>> +               clear_page_tag_ref(page);
>>                  return false;
>>          }
>>
>> --
>> 2.25.1
>>