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Date:   Mon, 17 Feb 2020 15:13:01 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zhihao Cheng <chengzhihao1@...wei.com>
Cc:     richard@....at, sashal@...nel.org, yi.zhang@...wei.com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Stable@...r.kernel.org
Subject: Re: [PATCH 4.4] ubifs: Fix deadlock in concurrent bulk-read and
 writepage

On Mon, Feb 17, 2020 at 08:23:59PM +0800, Zhihao Cheng wrote:
> [ Upstream commit f5de5b83303e61b1f3fb09bd77ce3ac2d7a475f2 ]
> 
> In ubifs, concurrent execution of writepage and bulk read on the same file
> may cause ABBA deadlock, for example (Reproduce method see Link):
> 
> Process A(Bulk-read starts from page4)         Process B(write page4 back)
>   vfs_read                                       wb_workfn or fsync
>   ...                                            ...
>   generic_file_buffered_read                     write_cache_pages
>     ubifs_readpage                                 LOCK(page4)
> 
>       ubifs_bulk_read                              ubifs_writepage
>         LOCK(ui->ui_mutex)                           ubifs_write_inode
> 
> 	  ubifs_do_bulk_read                           LOCK(ui->ui_mutex)
> 	    find_or_create_page(alloc page4)                  ↑
> 	      LOCK(page4)                   <--     ABBA deadlock occurs!
> 
> In order to ensure the serialization execution of bulk read, we can't
> remove the big lock 'ui->ui_mutex' in ubifs_bulk_read(). Instead, we
> allow ubifs_do_bulk_read() to lock page failed by replacing
> find_or_create_page(FGP_LOCK) with
> pagecache_get_page(FGP_LOCK | FGP_NOWAIT).
> 
> Signed-off-by: Zhihao Cheng <chengzhihao1@...wei.com>
> Suggested-by: zhangyi (F) <yi.zhang@...wei.com>
> Cc: <Stable@...r.kernel.org>
> Fixes: 4793e7c5e1c ("UBIFS: add bulk-read facility")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206153
> Signed-off-by: Richard Weinberger <richard@....at>
> ---
>  fs/ubifs/file.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
> index b895af7d8d80..e6d0a7df341d 100644
> --- a/fs/ubifs/file.c
> +++ b/fs/ubifs/file.c
> @@ -782,8 +782,9 @@ static int ubifs_do_bulk_read(struct ubifs_info *c, struct bu_info *bu,
>  
>  		if (page_offset > end_index)
>  			break;
> -		page = find_or_create_page(mapping, page_offset,
> -					   GFP_NOFS | __GFP_COLD);
> +		page = pagecache_get_page(mapping, page_offset,
> +				 FGP_LOCK|FGP_ACCESSED|FGP_CREAT|FGP_NOWAIT,
> +				 GFP_NOFS | __GFP_COLD);
>  		if (!page)
>  			break;
>  		if (!PageUptodate(page))
> -- 
> 2.7.4
> 

Now applied, thanks!

greg k-h

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