Date: Thu, 4 Jan 2024 22:36:44 +0100
From: David Hildenbrand <david@...hat.com>
To: "Yin, Fengwei" <fengwei.yin@...el.com>,
 syzbot <syzbot+50ef73537bbc393a25bb@...kaller.appspotmail.com>,
 akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 ryan.roberts@....com, syzkaller-bugs@...glegroups.com,
 Matthew Wilcox <willy@...radead.org>
Subject: Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity_checks

On 03.01.24 15:16, Yin, Fengwei wrote:
> 
> 
> On 1/3/2024 8:13 PM, David Hildenbrand wrote:
>> On 03.01.24 12:48, syzbot wrote:
>>> Hello,
>>>
>>> syzbot found the following issue on:
>>>
>>> HEAD commit:    ab0b3e6ef50d Add linux-next specific files for 20240102
>>> git tree:       linux-next
>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=17be3e09e80000
>>> kernel config:
>>> https://syzkaller.appspot.com/x/.config?x=a14a6350374945f9
>>> dashboard link:
>>> https://syzkaller.appspot.com/bug?extid=50ef73537bbc393a25bb
>>> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils
>>> for Debian) 2.40
>>> syz repro:
>>> https://syzkaller.appspot.com/x/repro.syz?x=14e2256ee80000
>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17b57db5e80000
>>>
>>> Downloadable assets:
>>> disk image:
>>> https://storage.googleapis.com/syzbot-assets/4e6376fe5764/disk-ab0b3e6e.raw.xz
>>> vmlinux:
>>> https://storage.googleapis.com/syzbot-assets/7cb9ecbaf001/vmlinux-ab0b3e6e.xz
>>> kernel image:
>>> https://storage.googleapis.com/syzbot-assets/2c1a9a6d424f/bzImage-ab0b3e6e.xz
>>>
>>> The issue was bisected to:
>>>
>>> commit 68f0320824fa59c5429cbc811e6c46e7a30ea32c
>>> Author: David Hildenbrand <david@...hat.com>
>>> Date:   Wed Dec 20 22:44:31 2023 +0000
>>>
>>>       mm/rmap: convert folio_add_file_rmap_range() into
>>> folio_add_file_rmap_[pte|ptes|pmd]()
>>>
>>> bisection log:
>>> https://syzkaller.appspot.com/x/bisect.txt?x=10b9e1b1e80000
>>> final oops:
>>> https://syzkaller.appspot.com/x/report.txt?x=12b9e1b1e80000
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=14b9e1b1e80000
>>>
>>> IMPORTANT: if you fix the issue, please add the following tag to the
>>> commit:
>>> Reported-by: syzbot+50ef73537bbc393a25bb@...kaller.appspotmail.com
>>> Fixes: 68f0320824fa ("mm/rmap: convert folio_add_file_rmap_range()
>>> into folio_add_file_rmap_[pte|ptes|pmd]()")
>>>
>>>    kasan_quarantine_reduce+0x18e/0x1d0 mm/kasan/quarantine.c:283
>>>    __kasan_slab_alloc+0x65/0x90 mm/kasan/common.c:324
>>>    kasan_slab_alloc include/linux/kasan.h:201 [inline]
>>>    slab_post_alloc_hook mm/slub.c:3813 [inline]
>>>    slab_alloc_node mm/slub.c:3860 [inline]
>>>    kmem_cache_alloc+0x136/0x320 mm/slub.c:3867
>>>    vm_area_alloc+0x1f/0x220 kernel/fork.c:465
>>>    mmap_region+0x3ae/0x2a90 mm/mmap.c:2804
>>>    do_mmap+0x890/0xef0 mm/mmap.c:1379
>>>    vm_mmap_pgoff+0x1a7/0x3c0 mm/util.c:573
>>>    ksys_mmap_pgoff+0x421/0x5a0 mm/mmap.c:1425
>>>    __do_sys_mmap arch/x86/kernel/sys_x86_64.c:93 [inline]
>>>    __se_sys_mmap arch/x86/kernel/sys_x86_64.c:86 [inline]
>>>    __x64_sys_mmap+0x125/0x190 arch/x86/kernel/sys_x86_64.c:86
>>>    do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>>>    do_syscall_64+0xd0/0x250 arch/x86/entry/common.c:83
>>>    entry_SYSCALL_64_after_hwframe+0x62/0x6a
>>> ------------[ cut here ]------------
>>> WARNING: CPU: 1 PID: 5059 at include/linux/rmap.h:202
>>> __folio_rmap_sanity_checks+0x4d5/0x630 include/linux/rmap.h:202
>>> Modules linked in:
>>> CPU: 1 PID: 5059 Comm: syz-executor115 Not tainted
>>> 6.7.0-rc8-next-20240102-syzkaller #0
>>> Hardware name: Google Google Compute Engine/Google Compute Engine,
>>> BIOS Google 11/17/2023
>>> RIP: 0010:__folio_rmap_sanity_checks+0x4d5/0x630 include/linux/rmap.h:202
>>> Code: 41 83 e4 01 44 89 e6 e8 79 bc b7 ff 45 84 e4 0f 85 08 fc ff ff
>>> e8 3b c1 b7 ff 48 c7 c6 e0 b5 d9 8a 48 89 df e8 5c 12 f7 ff 90 <0f> 0b
>>> 90 e9 eb fb ff ff e8 1e c1 b7 ff be 01 00 00 00 48 89 df e8
>>> RSP: 0018:ffffc900038df978 EFLAGS: 00010293
>>> RAX: 0000000000000000 RBX: ffffea00008cde00 RCX: ffffffff81687419
>>> RDX: ffff88807becbb80 RSI: ffffffff81d06104 RDI: 0000000000000000
>>> RBP: ffffea00008cde00 R08: 0000000000000000 R09: fffffbfff1e75f6a
>>> R10: ffffffff8f3afb57 R11: 0000000000000001 R12: 0000000000000000
>>> R13: 0000000000000001 R14: 0000000000000000 R15: dffffc0000000000
>>> FS:  0000555556508380(0000) GS:ffff8880b9900000(0000)
>>> knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: 00000000200000c0 CR3: 0000000079000000 CR4: 00000000003506f0
>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>> Call Trace:
>>>    <TASK>
>>>    __folio_add_rmap mm/rmap.c:1167 [inline]
>>>    __folio_add_file_rmap mm/rmap.c:1452 [inline]
>>>    folio_add_file_rmap_ptes+0x8e/0x2c0 mm/rmap.c:1478
>>>    insert_page_into_pte_locked.isra.0+0x34d/0x960 mm/memory.c:1874
>>>    insert_page mm/memory.c:1900 [inline]
>>>    vm_insert_page+0x62c/0x8c0 mm/memory.c:2053
>>>    packet_mmap+0x314/0x570 net/packet/af_packet.c:4594
>>>    call_mmap include/linux/fs.h:2090 [inline]
>>>    mmap_region+0x745/0x2a90 mm/mmap.c:2819
>>>    do_mmap+0x890/0xef0 mm/mmap.c:1379
>>>    vm_mmap_pgoff+0x1a7/0x3c0 mm/util.c:573
>>>    ksys_mmap_pgoff+0x421/0x5a0 mm/mmap.c:1425
>>>    __do_sys_mmap arch/x86/kernel/sys_x86_64.c:93 [inline]
>>>    __se_sys_mmap arch/x86/kernel/sys_x86_64.c:86 [inline]
>>>    __x64_sys_mmap+0x125/0x190 arch/x86/kernel/sys_x86_64.c:86
>>>    do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>>>    do_syscall_64+0xd0/0x250 arch/x86/entry/common.c:83
>>>    entry_SYSCALL_64_after_hwframe+0x62/0x6a
>>
>> If I am not wrong, that triggers:
>>
>> VM_WARN_ON_FOLIO(folio_test_large(folio) &&
>>            !folio_test_large_rmappable(folio), folio);
>>
>> So we are trying to rmap a large folio that did not go through
>> folio_prep_large_rmappable().
>>
>> net/packet/af_packet.c calls vm_insert_page() on some pages/folios stoed
>> in the "struct packet_ring_buffer". No idea where that comes from, but I
>> suspect it's simply some compound allocation.
> Looks like:
>    alloc_pg_vec
>      alloc_one_pg_vec_page
>           gfp_t gfp_flags = GFP_KERNEL | __GFP_COMP |
>                             __GFP_ZERO | __GFP_NOWARN | __GFP_NORETRY;
> 
>           buffer = (char *) __get_free_pages(gfp_flags, order);
> So you are right here... :).

Hm, but I wonder if this something that's supposed to work or is this 
one of the cases where we should actually use a VM_PFN mapping?

It's not a pagecache(file/shmem) page after all.

We could relax that check and document why we expect something that is 
not marked rmappable. But it fells wrong. I suspect this should be a 
VM_PFNMAP instead (like recent udmabuf changes).

-- 
Cheers,

David / dhildenb

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