[PATCH] erofs: avoid unnecessary loops in z_erofs_pcluster_readmore() when read page beyond EOF

[PATCH] erofs: avoid unnecessary loops in z_erofs_pcluster_readmore() when read page beyond EOF

[Chunhai Guo]

z_erofs_pcluster_readmore() may take a long time to loop when the page
offset is large enough, which is unnecessary should be prevented.
For example, when the following case is encountered, it will loop 4691368
times, taking about 27 seconds.
    - offset = 19217289215
    - inode_size = 1442672

Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
---
 fs/erofs/zdata.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 5f1890e309c6..d9a0763f4595 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1841,7 +1841,7 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f,
 	}
 
 	cur = map->m_la + map->m_llen - 1;
-	while (cur >= end) {
+	while ((cur >= end) && (cur < i_size_read(inode))) {
 		pgoff_t index = cur >> PAGE_SHIFT;
 		struct page *page;
 
-- 
2.25.1

Re: [PATCH] erofs: avoid unnecessary loops in z_erofs_pcluster_readmore() when read page beyond EOF

[Gao Xiang]

On 2023/7/10 12:25, Chunhai Guo wrote:
> z_erofs_pcluster_readmore() may take a long time to loop when the page
> offset is large enough, which is unnecessary should be prevented.
> For example, when the following case is encountered, it will loop 4691368
> times, taking about 27 seconds.
>      - offset = 19217289215
>      - inode_size = 1442672
> 
> Signed-off-by: Chunhai Guo <guochunhai@vivo.com>

It looks good to me,

Fixes: 386292919c25 ("erofs: introduce readmore decompression strategy")
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Thanks,
Gao Xiang

Re: [PATCH] erofs: avoid unnecessary loops in z_erofs_pcluster_readmore() when read page beyond EOF

[Yue Hu]

On Mon, 10 Jul 2023 12:25:31 +0800
Chunhai Guo <guochunhai@vivo.com> wrote:

> z_erofs_pcluster_readmore() may take a long time to loop when the page
> offset is large enough, which is unnecessary should be prevented.
> For example, when the following case is encountered, it will loop 4691368
> times, taking about 27 seconds.
>     - offset = 19217289215
>     - inode_size = 1442672
> 
> Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
> ---
>  fs/erofs/zdata.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index 5f1890e309c6..d9a0763f4595 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -1841,7 +1841,7 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f,
>  	}
>  
>  	cur = map->m_la + map->m_llen - 1;
> -	while (cur >= end) {
> +	while ((cur >= end) && (cur < i_size_read(inode))) {
>  		pgoff_t index = cur >> PAGE_SHIFT;
>  		struct page *page;
>  

Reviewed-by: Yue Hu <huyue2@coolpad.com>

Re: [PATCH] erofs: avoid unnecessary loops in z_erofs_pcluster_readmore() when read page beyond EOF

[Gao Xiang]

On 2023/7/10 12:25, Chunhai Guo wrote:
> z_erofs_pcluster_readmore() may take a long time to loop when the page
> offset is large enough, which is unnecessary should be prevented.
> For example, when the following case is encountered, it will loop 4691368
> times, taking about 27 seconds.
>      - offset = 19217289215
>      - inode_size = 1442672
> 
> Signed-off-by: Chunhai Guo <guochunhai@vivo.com>

I will update the subject manually to:
"erofs: avoid useless loops in z_erofs_pcluster_readmore() when reading beyond EOF"

to avoid overly long subject as well...

Thanks,
Gao Xiang

Re: [PATCH] erofs: avoid unnecessary loops in z_erofs_pcluster_readmore() when read page beyond EOF

[Chao Yu]

On 2023/7/10 12:25, Chunhai Guo wrote:
> z_erofs_pcluster_readmore() may take a long time to loop when the page
> offset is large enough, which is unnecessary should be prevented.
> For example, when the following case is encountered, it will loop 4691368
> times, taking about 27 seconds.
>      - offset = 19217289215
>      - inode_size = 1442672
> 
> Signed-off-by: Chunhai Guo <guochunhai@vivo.com>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,