linux-kernel - Re: [PATCH 2/2] erofs: get correct count for unmapped range in fscache mode

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Message-ID: <Y2TjjsZFNYp66sNJ@B-P7TQMD6M-0146.local>
Date:   Fri, 4 Nov 2022 18:03:58 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Jingbo Xu <jefflexu@...ux.alibaba.com>
Cc:     xiang@...nel.org, chao@...nel.org, huyue2@...lpad.com,
        linux-erofs@...ts.ozlabs.org, zhujia.zj@...edance.com,
        yinxin.x@...edance.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] erofs: get correct count for unmapped range in
 fscache mode

On Fri, Nov 04, 2022 at 01:40:28PM +0800, Jingbo Xu wrote:
> For unmapped range, the returned map.m_llen is zero, and thus the
> calculated count is unexpected zero.
> 
> Prior to the refactoring introduced by commit 1ae9470c3e14 ("erofs:
> clean up .read_folio() and .readahead() in fscache mode"), only the
> readahead routine suffers from this. With the refactoring of making
> .read_folio() and .readahead() calling one common routine, both
> read_folio and readahead have this issue now.
> 
> Fix this by calculating count separately in unmapped condition.
> 
> Fixes: c665b394b9e8 ("erofs: implement fscache-based data readahead")
> Fixes: 1ae9470c3e14 ("erofs: clean up .read_folio() and .readahead() in fscache mode")
> Signed-off-by: Jingbo Xu <jefflexu@...ux.alibaba.com>

Reviewed-by: Gao Xiang <hsiangkao@...ux.alibaba.com>

Thanks,
Gao Xiang

> ---
>  fs/erofs/fscache.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index 83559008bfa8..260fa4737fc0 100644
> --- a/fs/erofs/fscache.c
> +++ b/fs/erofs/fscache.c
> @@ -296,15 +296,16 @@ static int erofs_fscache_data_read(struct address_space *mapping,
>  		return PAGE_SIZE;
>  	}
>  
> -	count = min_t(size_t, map.m_llen - (pos - map.m_la), len);
> -	DBG_BUGON(!count || count % PAGE_SIZE);
> -
>  	if (!(map.m_flags & EROFS_MAP_MAPPED)) {
> +		count = len;
>  		iov_iter_xarray(&iter, READ, &mapping->i_pages, pos, count);
>  		iov_iter_zero(count, &iter);
>  		return count;
>  	}
>  
> +	count = min_t(size_t, map.m_llen - (pos - map.m_la), len);
> +	DBG_BUGON(!count || count % PAGE_SIZE);
> +
>  	mdev = (struct erofs_map_dev) {
>  		.m_deviceid = map.m_deviceid,
>  		.m_pa = map.m_pa,
> -- 
> 2.19.1.6.gb485710b