linux-kernel - [PATCH] mm, fs: avoid page allocation beyond i

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Message-Id: <1377099441-2224-1-git-send-email-kirill.shutemov@linux.intel.com>
Date:	Wed, 21 Aug 2013 18:37:21 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dave Hansen <dave.hansen@...ux.intel.com>, Jan Kara <jack@...e.cz>,
	Al Viro <viro@...iv.linux.org.uk>, NeilBrown <neilb@...e.de>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH] mm, fs: avoid page allocation beyond i_size on read

I've noticed that we allocated unneeded page for cache on read beyond
i_size. Simple test case (I checked it on ramfs):

$ touch testfile
$ cat testfile

It triggers 'no_cached_page' code path in do_generic_file_read().

Looks like it's regression since commit a32ea1e. Let's fix it.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Acked-by: NeilBrown <neilb@...e.de>
---
 mm/filemap.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index 1905f0e..b1a4d35 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1163,6 +1163,10 @@ static void do_generic_file_read(struct file *filp, loff_t *ppos,
 		loff_t isize;
 		unsigned long nr, ret;
 
+		isize = i_size_read(inode);
+		if (!isize || index > (isize - 1) >> PAGE_CACHE_SHIFT)
+			goto out;
+
 		cond_resched();
 find_page:
 		page = find_get_page(mapping, index);
-- 
1.8.4.rc2

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