linux-kernel - [PATCH] erofs: avoid unnecessary loops in z_erofs_pcluster

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Message-Id: <20230710042531.28761-1-guochunhai@vivo.com>
Date:   Mon, 10 Jul 2023 12:25:31 +0800
From:   Chunhai Guo <guochunhai@...o.com>
To:     xiang@...nel.org, chao@...nel.org
Cc:     huyue2@...lpad.com, jefflexu@...ux.alibaba.com,
        linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Chunhai Guo <guochunhai@...o.com>
Subject: [PATCH] erofs: avoid unnecessary loops in z_erofs_pcluster_readmore() when read page beyond EOF

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@...o.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