Re: [PATCH 1/4] erofs: fix setting up pcluster for temporary pages

[Vladimir Zapolskiy]

Hello Gao Xiang,

On 10/22/20 5:57 PM, Gao Xiang via Linux-erofs wrote:
> From: Gao Xiang <hsiangkao@xxxxxxxxxx>
>
> pcluster should be only set up for all managed pages instead of
> temporary pages. Since it currently uses page->mapping to identify,
> the impact is minor for now.
>
> Fixes: 5ddcee1f3a1c ("erofs: get rid of __stagingpage_alloc helper")
> Cc: <stable@xxxxxxxxxxxxxxx> # 5.5+
> Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxx>

I was looking exactly at this problem recently, my change is one-to-one
to your fix, thus I can provide a tag:

Tested-by: Vladimir Zapolskiy <vladimir@xxxxxxxxxx>


The fixed problem is minor, but the kernel log becomes polluted, if
a page allocation debug option is enabled:

    % md5sum ~/erofs/testfile
    BUG: Bad page state in process kworker/u9:0  pfn:687de
    page:0000000057b8bcb4 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x687de
    flags: 0x4000000000002000(private)
    raw: 4000000000002000 dead000000000100 dead000000000122 0000000000000000
    raw: 0000000000000000 ffff888066758690 00000000ffffffff 0000000000000000
    page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
    Modules linked in:
    CPU: 1 PID: 602 Comm: kworker/u9:0 Not tainted 5.9.1 #2
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
    Workqueue: erofs_unzipd z_erofs_decompressqueue_work
    Call Trace:
     dump_stack+0x84/0xba
     bad_page.cold+0xac/0xb1
     check_free_page_bad+0xb0/0xc0
     free_pcp_prepare+0x2c8/0x2d0
     free_unref_page+0x18/0xf0
     put_pages_list+0x11a/0x120
     z_erofs_decompressqueue_work+0xc9/0x110
     ? z_erofs_decompress_pcluster.isra.0+0xf10/0xf10
     ? read_word_at_a_time+0x12/0x20
     ? strscpy+0xc7/0x1a0
     process_one_work+0x30c/0x730
     worker_thread+0x91/0x640
     ? __kasan_check_read+0x11/0x20
     ? rescuer_thread+0x8a0/0x8a0
     kthread+0x1dd/0x200
     ? kthread_unpark+0xa0/0xa0
     ret_from_fork+0x1f/0x30
    Disabling lock debugging due to kernel taint

--
Best wishes,
Vladimir