linux-kernel - Re: [PATCH] f2fs: avoid race between zero

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Message-ID: <20180727102916.GI16155@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Fri, 27 Jul 2018 19:29:16 +0900
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH] f2fs: avoid race between zero_range and background GC

On 07/26, Chao Yu wrote:
> Thread A				Background GC
> - f2fs_zero_range
>  - truncate_pagecache_range
> 					- gc_data_segment
> 					 - get_read_data_page
> 					  - move_data_page
> 					   - set_page_dirty
> 					   - set_cold_data
>  - f2fs_do_zero_range
>   - dn->data_blkaddr = NEW_ADDR;
>   - f2fs_set_data_blkaddr
> 
> Actually, we don't need to set dirty & checked flag on the page, since
> all valid data in the page should be zeroed by zero_range().

But, it doesn't matter too much, right?

> Use i_gc_rwsem[WRITE] to avoid such race condition.

Hope to avoid abusing i_gc_rwsem[] tho.

> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/file.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 267ec3794e1e..7bd2412a8c37 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1309,6 +1309,7 @@ static int f2fs_zero_range(struct inode *inode, loff_t offset, loff_t len,
>  	if (ret)
>  		return ret;
>  
> +	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>  	down_write(&F2FS_I(inode)->i_mmap_sem);
>  	ret = filemap_write_and_wait_range(mapping, offset, offset + len - 1);
>  	if (ret)
> @@ -1389,6 +1390,7 @@ static int f2fs_zero_range(struct inode *inode, loff_t offset, loff_t len,
>  	}
>  out_sem:
>  	up_write(&F2FS_I(inode)->i_mmap_sem);
> +	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>  
>  	return ret;
>  }
> -- 
> 2.18.0.rc1