Re: general protection fault in wb_timer_fn

[Hao Sun <sunhao.th@gmail.com>]

> The BUG is triggered if it tries to invalidate across pages. But it
> hardcoded PAGE_SIZE. The offset passed in by truncate_cleanup_page()
> is 0, but the length might be > PAGE_SIZE if it is a compound page. It
> might be caused by READ_ONLY_THP_FOR_FS.
>
> Could you please try the below debug patch to dump page details? I saw
> your kernel config has DEBUG_VM enabled.
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index ab7573d72dd7..ed7256112c2b 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1507,7 +1507,8 @@ void block_invalidatepage(struct page *page,
> unsigned int offset,
>         /*
>          * Check for overflow
>          */
> -       BUG_ON(stop > PAGE_SIZE || stop < length);
> +       VM_BUG_ON_PAGE((stop > PAGE_SIZE), page);
> +       VM_BUG_ON_PAGE((stop < length), page);
>
>         head = page_buffers(page);
>         bh = head;
>

Just patched it.
The following log was printed after executing the C reproducer.

IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): wlan1: link becomes ready
Bluetooth: hci0: command 0x0409 tx timeout
Bluetooth: hci0: command 0x041b tx timeout
Bluetooth: hci0: command 0x040f tx timeout
Bluetooth: hci0: command 0x0419 tx timeout
page:ffffea00009c0000 refcount:514 mapcount:0 mapping:ffff8881060db7b0
index:0x0 pfn:0x27000
head:ffffea00009c0000 order:9 compound_mapcount:0 compound_pincount:0
memcg:ffff8880118bc000
aops:def_blk_aops ino:fa00000
flags: 0xfff00000012037(locked|referenced|uptodate|lru|active|private|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000012037 ffffea00009491c8 ffff888010c7d030 ffff8881060db7b0
raw: 0000000000000000 ffff888025d10658 00000202ffffffff ffff8880118bc000
page dumped because: VM_BUG_ON_PAGE((stop > ((1UL) << 12)))
page_owner tracks the page as allocated
page last allocated via order 9, migratetype Movable, gfp_mask
0x13c24ca(GFP_TRANSHUGE|__GFP_THISNODE), pid 35, ts 579054356699,
free_ts 543915753195
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook mm/page_alloc.c:2418 [inline]
 prep_new_page+0x1a5/0x240 mm/page_alloc.c:2424
 get_page_from_freelist+0x1f10/0x3b70 mm/page_alloc.c:4153
 __alloc_pages+0x306/0x6e0 mm/page_alloc.c:5375
 __alloc_pages_node include/linux/gfp.h:570 [inline]
 khugepaged_alloc_page+0xa0/0x170 mm/khugepaged.c:881
 collapse_file+0x20a/0x45f0 mm/khugepaged.c:1655
 khugepaged_scan_file mm/khugepaged.c:2051 [inline]
 khugepaged_scan_mm_slot mm/khugepaged.c:2146 [inline]
 khugepaged_do_scan mm/khugepaged.c:2230 [inline]
 khugepaged+0x2e65/0x5c50 mm/khugepaged.c:2275
 kthread+0x3e5/0x4d0 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1338 [inline]
 free_pcp_prepare+0x412/0x900 mm/page_alloc.c:1389
 free_unref_page_prepare mm/page_alloc.c:3315 [inline]
 free_unref_page+0x19/0x580 mm/page_alloc.c:3394
 release_pages+0x87f/0x2920 mm/swap.c:926
 tlb_batch_pages_flush mm/mmu_gather.c:49 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:242 [inline]
 tlb_flush_mmu+0x8d/0x610 mm/mmu_gather.c:249
 tlb_finish_mmu+0x93/0x3c0 mm/mmu_gather.c:340
 unmap_region+0x27f/0x350 mm/mmap.c:2653
 __do_munmap+0xabc/0x11e0 mm/mmap.c:2884
 do_munmap mm/mmap.c:2895 [inline]
 munmap_vma_range mm/mmap.c:603 [inline]
 mmap_region+0x2c4/0x1340 mm/mmap.c:1742
 do_mmap+0x7f5/0xe60 mm/mmap.c:1575
 vm_mmap_pgoff+0x1b7/0x290 mm/util.c:519
 ksys_mmap_pgoff+0x49f/0x620 mm/mmap.c:1624
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
------------[ cut here ]------------
kernel BUG at fs/buffer.c:1511!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 2954 Comm: kworker/1:2 Not tainted 5.15.0-rc1+ #4
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
Workqueue: events delayed_fput
RIP: 0010:block_invalidatepage+0x599/0x680 fs/buffer.c:1511
Code: 0f 0b e8 9a 6b 9c ff 31 f6 4c 89 e7 e8 10 d7 bf ff e9 df fe ff
ff e8 86 6b 9c ff 48 c7 c6 00 4e 9a 89 4c 89 e7 e8 c7 16 d0 ff <0f> 0b
e8 70 6b 9c ff 48 c7 c6 60 4e 9a 89 4c 89 e7 e8 b1 16 d0 ff
RSP: 0018:ffffc9000e9078b8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff888100bd9c80
RDX: 0000000000000000 RSI: ffff888100bd9c80 RDI: 0000000000000002
RBP: 0000000000000000 R08: ffffffff81d9e369 R09: 000000000000ffff
R10: 0000000000000003 R11: ffffed1026b83f53 R12: ffffea00009c0000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000200000
FS:  0000000000000000(0000) GS:ffff888135c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffde41e8960 CR3: 0000000019cef000 CR4: 0000000000350ee0
Call Trace:
 do_invalidatepage mm/truncate.c:157 [inline]
 truncate_cleanup_page+0x3e4/0x620 mm/truncate.c:176
 truncate_inode_pages_range+0x26c/0x1910 mm/truncate.c:325
 kill_bdev.isra.0+0x5f/0x80 block/bdev.c:77
 blkdev_flush_mapping+0xdf/0x2e0 block/bdev.c:658
 blkdev_put_whole+0xe8/0x110 block/bdev.c:689
 blkdev_put+0x23c/0x6f0 block/bdev.c:953
 blkdev_close+0x8d/0xb0 block/fops.c:459
 __fput+0x288/0x9f0 fs/file_table.c:280
 delayed_fput+0x56/0x70 fs/file_table.c:308
 process_one_work+0x9df/0x16d0 kernel/workqueue.c:2297
 worker_thread+0x90/0xed0 kernel/workqueue.c:2444
 kthread+0x3e5/0x4d0 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
Modules linked in:
Dumping ftrace buffer:
   (ftrace buffer empty)
---[ end trace 77cfca54575c5255 ]---
RIP: 0010:block_invalidatepage+0x599/0x680 fs/buffer.c:1511
Code: 0f 0b e8 9a 6b 9c ff 31 f6 4c 89 e7 e8 10 d7 bf ff e9 df fe ff
ff e8 86 6b 9c ff 48 c7 c6 00 4e 9a 89 4c 89 e7 e8 c7 16 d0 ff <0f> 0b
e8 70 6b 9c ff 48 c7 c6 60 4e 9a 89 4c 89 e7 e8 b1 16 d0 ff
RSP: 0018:ffffc9000e9078b8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff888100bd9c80
RDX: 0000000000000000 RSI: ffff888100bd9c80 RDI: 0000000000000002
RBP: 0000000000000000 R08: ffffffff81d9e369 R09: 000000000000ffff
R10: 0000000000000003 R11: ffffed1026b83f53 R12: ffffea00009c0000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000200000
FS:  0000000000000000(0000) GS:ffff888135c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f78dffb7ef8 CR3: 000000001f2ef000 CR4: 0000000000350ee0


> If my speculation is correct, I think the below patch should be able
> to fix this issue.
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index ab7573d72dd7..18428cee59af 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1507,7 +1507,7 @@ void block_invalidatepage(struct page *page,
> unsigned int offset,
>         /*
>          * Check for overflow
>          */
> -       BUG_ON(stop > PAGE_SIZE || stop < length);
> +       BUG_ON(stop > thp_size(page) || stop < length);
>
>         head = page_buffers(page);
>         bh = head;
>

Yes, the C reproducer can not crash the kernel anymore after patching
the above code.