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

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Date:   Fri, 30 Oct 2020 14:20:31 +0200
From:   Vladimir Zapolskiy <vladimir@...era.com>
To:     <linux-erofs@...ts.ozlabs.org>, Gao Xiang <hsiangkao@...hat.com>
CC:     Gao Xiang <hsiangkao@....com>, <stable@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] erofs: fix setting up pcluster for temporary pages

Hello Gao Xiang,

On 10/22/20 5:57 PM, Gao Xiang via Linux-erofs wrote:
> From: Gao Xiang <hsiangkao@...hat.com>
> 
> 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@...r.kernel.org> # 5.5+
> Signed-off-by: Gao Xiang <hsiangkao@...hat.com>

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@...era.com>


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