Date:   Mon, 12 Dec 2022 10:50:44 -0800
From:   Sidhartha Kumar <sidhartha.kumar@...cle.com>
To:     David Hildenbrand <david@...hat.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-kernel@...r.kernel.org,
        Linux Memory Management List <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Muchun Song <songmuchun@...edance.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mina Almasry <almasrymina@...gle.com>,
        Miaohe Lin <linmiaohe@...wei.com>, hughd@...gle.com,
        tsahu@...ux.ibm.com, jhubbard@...dia.com
Subject: Re: [PATCH mm-unstable v5 01/10] mm: add folio dtor and order setter
 functions

On 12/12/22 10:34 AM, David Hildenbrand wrote:
> On 07.12.22 05:11, Muchun Song wrote:
>>
>>
>>> On Dec 7, 2022, at 11:42, Mike Kravetz <mike.kravetz@...cle.com> wrote:
>>>
>>> On 12/07/22 11:34, Muchun Song wrote:
>>>>
>>>>
>>>>> On Nov 30, 2022, at 06:50, Sidhartha Kumar 
>>>>> <sidhartha.kumar@...cle.com> wrote:
>>>>>
>>>>> Add folio equivalents for set_compound_order() and 
>>>>> set_compound_page_dtor().
>>>>>
>>>>> Also remove extra new-lines introduced by mm/hugetlb: convert
>>>>> move_hugetlb_state() to folios and mm/hugetlb_cgroup: convert
>>>>> hugetlb_cgroup_uncharge_page() to folios.
>>>>>
>>>>> Suggested-by: Mike Kravetz <mike.kravetz@...cle.com>
>>>>> Suggested-by: Muchun Song <songmuchun@...edance.com>
>>>>> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
>>>>> ---
>>>>> include/linux/mm.h | 16 ++++++++++++++++
>>>>> mm/hugetlb.c       |  4 +---
>>>>> 2 files changed, 17 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>>>> index a48c5ad16a5e..2bdef8a5298a 100644
>>>>> --- a/include/linux/mm.h
>>>>> +++ b/include/linux/mm.h
>>>>> @@ -972,6 +972,13 @@ static inline void 
>>>>> set_compound_page_dtor(struct page *page,
>>>>> page[1].compound_dtor = compound_dtor;
>>>>> }
>>>>>
>>>>> +static inline void folio_set_compound_dtor(struct folio *folio,
>>>>> + enum compound_dtor_id compound_dtor)
>>>>> +{
>>>>> + VM_BUG_ON_FOLIO(compound_dtor >= NR_COMPOUND_DTORS, folio);
>>>>> + folio->_folio_dtor = compound_dtor;
>>>>> +}
>>>>> +
>>>>> void destroy_large_folio(struct folio *folio);
>>>>>
>>>>> static inline int head_compound_pincount(struct page *head)
>>>>> @@ -987,6 +994,15 @@ static inline void set_compound_order(struct 
>>>>> page *page, unsigned int order)
>>>>> #endif
>>>>> }
>>>>>
>>>>> +static inline void folio_set_compound_order(struct folio *folio,
>>>>> + unsigned int order)
>>>>> +{
>>>>> + folio->_folio_order = order;
>>>>> +#ifdef CONFIG_64BIT
>>>>> + folio->_folio_nr_pages = order ? 1U << order : 0;
>>>>
>>>> It seems that you think the user could pass 0 to order. However,
>>>> ->_folio_nr_pages and ->_folio_order fields are invalid for order-0 
>>>> pages.
>>>> You should not touch it. So this should be:
>>>>
>>>> static inline void folio_set_compound_order(struct folio *folio,
>>>>      unsigned int order)
>>>> {
>>>>     if (!folio_test_large(folio))
>>>>         return;
>>>>
>>>>     folio->_folio_order = order;
>>>> #ifdef CONFIG_64BIT
>>>>     folio->_folio_nr_pages = 1U << order;
>>>> #endif
>>>> }
>>>
>>> I believe this was changed to accommodate the code in
>>> __destroy_compound_gigantic_page().  It is used in a subsequent patch.
>>> Here is the v6.0 version of the routine.
>>
>> Thanks for your clarification.
>>
>>>
>>> static void __destroy_compound_gigantic_page(struct page *page,
>>> unsigned int order, bool demote)
>>> {
>>>     int i;
>>>     int nr_pages = 1 << order;
>>>     struct page *p = page + 1;
>>>
>>>     atomic_set(compound_mapcount_ptr(page), 0);
>>>     atomic_set(compound_pincount_ptr(page), 0);
>>>
>>>     for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
>>>         p->mapping = NULL;
>>>         clear_compound_head(p);
>>>         if (!demote)
>>>             set_page_refcounted(p);
>>>     }
>>>
>>>     set_compound_order(page, 0);
>>> #ifdef CONFIG_64BIT
>>>     page[1].compound_nr = 0;
>>> #endif
>>>     __ClearPageHead(page);
>>> }
>>>
>>>
>>> Might have been better to change this set_compound_order call to
>>> folio_set_compound_order in this patch.
>>>
>>
>> Agree. It has confused me a lot. I suggest changing the code to the
>> followings. The folio_test_large() check is still to avoid unexpected
>> users for OOB.
>>
>> static inline void folio_set_compound_order(struct folio *folio,
>>                         unsigned int order)
>> {
>>     VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>>     // or
>>     // if (!folio_test_large(folio))
>>     //     return;
>>
>>     folio->_folio_order = order;
>> #ifdef CONFIG_64BIT
>>     folio->_folio_nr_pages = order ? 1U << order : 0;
>> #endif
>> }
>>
>> Thanks.
> 
> On mm-stable, dynamically allocating gigantic pages gives me:
> 
> [   23.625105] page:00000000ae27bd2a refcount:1 mapcount:0 
> mapping:0000000000000000 index:0x0 pfn:0x1800
> [   23.635117] flags: 0x17fffc00000000(node=0|zone=2|lastcpupid=0x1ffff)
> [   23.641969] raw: 0017fffc00000000 ffffa4edc489bb58 fffff784c6000048 
> 0000000000000000
> [   23.650141] raw: 0000000000000000 0000000000000000 00000001ffffffff 
> 0000000000000000
> [   23.657907] page dumped because: 
> VM_BUG_ON_FOLIO(!folio_test_large(folio))


static bool __prep_compound_gigantic_folio(struct folio *folio,
					unsigned int order, bool demote)
{
	int i, j;
	int nr_pages = 1 << order;
	struct page *p;

	/* we rely on prep_new_hugetlb_folio to set the destructor */
	folio_set_compound_order(folio, order);
	__folio_clear_reserved(folio);
	__folio_set_head(folio);

The problem looks to be because the head flag is set after the call to 
folio_set_compound_order() which looks for PG_head. I will test the fix 
of moving folio_set_compound_order() to after the __folio_set_head() call.

> [   23.663955] ------------[ cut here ]------------
> [   23.667680] kernel BUG at include/linux/mm.h:1030!
> [   23.673378] invalid opcode: 0000 [#1] PREEMPT SMP PTI
> [   23.681610] CPU: 3 PID: 1220 Comm: bash Not tainted 6.1.0-rc4+ #13
> [   23.690281] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 
> 1.16.0-1.fc36 04/01/2014
> [   23.699837] RIP: 0010:__prep_compound_gigantic_folio+0x115/0x120
> [   23.706587] Code: c7 44 24 5c 00 00 00 00 5b 44 89 d0 5d 41 5c 41 5d 
> 41 5e c3 cc cc cc cc 48 83 e8 09
> [   23.725954] RSP: 0018:ffffa4edc489bc90 EFLAGS: 00010296
> [   23.731001] RAX: 000000000000003e RBX: ffffffffae39a720 RCX: 
> 0000000000000000
> [   23.736065] RDX: 0000000000000001 RSI: ffffffffad522c25 RDI: 
> 00000000ffffffff
> [   23.740866] RBP: 0000000000040000 R08: 0000000000000000 R09: 
> ffffa4edc489bb58
> [   23.745385] R10: 0000000000000003 R11: ffff926d7ff4b028 R12: 
> fffff784c6000000
> [   23.749464] R13: 0000000000040000 R14: fffff784c6000000 R15: 
> ffff9266039fb900
> [   23.753176] FS:  00007f69a9703740(0000) GS:ffff92696f8c0000(0000) 
> knlGS:0000000000000000
> [   23.758299] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   23.761275] CR2: 0000556789080640 CR3: 0000000105568005 CR4: 
> 0000000000770ee0
> [   23.764929] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 
> 0000000000000000
> [   23.768572] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 
> 0000000000000400
> [   23.772221] PKRU: 55555554
> [   23.773696] Call Trace:
> [   23.776170]  <TASK>
> [   23.777258]  alloc_fresh_hugetlb_folio+0x14b/0x220
> [   23.779406]  alloc_pool_huge_page+0x7c/0x110
> [   23.781273]  __nr_hugepages_store_common+0x191/0x400
> [   23.783369]  ? __mod_memcg_lruvec_state+0x93/0x110
> [   23.785343]  ? __mod_lruvec_page_state+0xa6/0x1a0
> [   23.787223]  ? _copy_from_iter+0x8c/0x540
> [   23.788788]  ? __kmem_cache_alloc_node+0x13b/0x2a0
> [   23.790577]  ? kernfs_fop_write_iter+0x174/0x1f0
> [   23.792313]  nr_hugepages_store+0x57/0x70
> [   23.793754]  kernfs_fop_write_iter+0x11b/0x1f0
> [   23.795337]  vfs_write+0x1e1/0x3a0
> [   23.796531]  ksys_write+0x53/0xd0
> [   23.797690]  do_syscall_64+0x37/0x90
> [   23.798947]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [   23.800602] RIP: 0033:0x7f69a9501977
> [   23.801798] Code: 0f 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 
> 1f 00 f3 0f 1e fa 64 8b 04 25 14
> [   23.807322] RSP: 002b:00007ffce87f3338 EFLAGS: 00000246 ORIG_RAX: 
> 0000000000000001
> [   23.809460] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 
> 00007f69a9501977
> [   23.811485] RDX: 0000000000000002 RSI: 00005652a970e5e0 RDI: 
> 0000000000000001
> [   23.813443] RBP: 00005652a970e5e0 R08: 0000000000000000 R09: 
> 0000000000000073
> [   23.815385] R10: 0000000000001000 R11: 0000000000000246 R12: 
> 0000000000000002
> [   23.817289] R13: 00007f69a95f9780 R14: 0000000000000002 R15: 
> 00007f69a95f49e0
> [   23.819176]  </TASK>
> [   23.819792] Modules linked in: intel_rapl_msr intel_rapl_common 
> intel_uncore_frequency_common isst_ir
> [   23.829056] ---[ end trace 0000000000000000 ]---
> [   23.830413] RIP: 0010:__prep_compound_gigantic_folio+0x115/0x120
> [   23.832390] Code: c7 44 24 5c 00 00 00 00 5b 44 89 d0 5d 41 5c 41 5d 
> 41 5e c3 cc cc cc cc 48 83 e8 09
> [   23.836787] RSP: 0018:ffffa4edc489bc90 EFLAGS: 00010296
> [   23.838083] RAX: 000000000000003e RBX: ffffffffae39a720 RCX: 
> 0000000000000000
> [   23.839764] RDX: 0000000000000001 RSI: ffffffffad522c25 RDI: 
> 00000000ffffffff
> [   23.841456] RBP: 0000000000040000 R08: 0000000000000000 R09: 
> ffffa4edc489bb58
> [   23.843150] R10: 0000000000000003 R11: ffff926d7ff4b028 R12: 
> fffff784c6000000
> [   23.844836] R13: 0000000000040000 R14: fffff784c6000000 R15: 
> ffff9266039fb900
> [   23.846521] FS:  00007f69a9703740(0000) GS:ffff92696f8c0000(0000) 
> knlGS:0000000000000000
> [   23.848417] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   23.849797] CR2: 0000556789080640 CR3: 0000000105568005 CR4: 
> 0000000000770ee0
> [   23.851491] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 
> 0000000000000000
> [   23.853181] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 
> 0000000000000400
> [   23.854861] PKRU: 55555554
> 
> 
> Something's broken.
> 

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