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Subject: Re: [PATCH V2] f2fs: fix the panic in do_checkpoint()
To:     Sahitya Tummala <stummala@codeaurora.org>,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>
CC:     <linux-kernel@vger.kernel.org>
References: <1581911024-23660-1-git-send-email-stummala@codeaurora.org>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <1c80288f-aea1-874b-4ca0-d18d00ed60e2@huawei.com>
Date:   Mon, 17 Feb 2020 14:37:17 +0800
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On 2020/2/17 11:43, Sahitya Tummala wrote:
> There could be a scenario where f2fs_sync_meta_pages() will not
> ensure that all F2FS_DIRTY_META pages are submitted for IO. Thus,
> resulting in the below panic in do_checkpoint() -
> 
> f2fs_bug_on(sbi, get_pages(sbi, F2FS_DIRTY_META) &&
> 				!f2fs_cp_error(sbi));
> 
> This can happen in a low-memory condition, where shrinker could
> also be doing the writepage operation (stack shown below)
> at the same time when checkpoint is running on another core.
> 
> schedule
> down_write
> f2fs_submit_page_write -> by this time, this page in page cache is tagged
> 			as PAGECACHE_TAG_WRITEBACK and PAGECACHE_TAG_DIRTY
> 			is cleared, due to which f2fs_sync_meta_pages()
> 			cannot sync this page in do_checkpoint() path.
> f2fs_do_write_meta_page
> __f2fs_write_meta_page
> f2fs_write_meta_page
> shrink_page_list
> shrink_inactive_list
> shrink_node_memcg
> shrink_node
> kswapd
> 
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>

Looks good to me.

Reviewed-by: Chao Yu <yuchao0@huawei.com>

BTW, I can't apply this based dev branch of Jaegeuk's tree, could you rebase it?

Thanks,