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Subject[RFC][PATCH] vfs: check inode size on no_cached_page
[This patch may not necessarily be merged, but at least we should
be aware of the problem.]

When user space requests past-EOF data, do_generic_file_read() will
issue a bonus readpage call, which may be unfavorable.

do_generic_file_read:
-> find_page:
-> find_get_page() = NULL
-> page_cache_sync_readahead()
-> find_get_page() = NULL
-> no_cached_page:
-> readpage:
-> nfs_readpage() = error
-> readpage_error:

Reported-by: Xu Chenfeng <xcf@ustc.edu.cn>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
mm/filemap.c | 5 +++++
1 file changed, 5 insertions(+)

--- mm.orig/mm/filemap.c
+++ mm/mm/filemap.c
@@ -1269,6 +1269,11 @@ readpage_error:
goto out;

no_cached_page:
+ isize = i_size_read(inode);
+ end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
+ if (unlikely(!isize || index > end_index))
+ goto out;
+
/*
* Ok, it wasn't cached, so we need to create a new
* page..

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