Bugzilla: 1078894
Upstream: 3.14 and sent to stable for 3.13.7

From 58d5640ebdb273cc817b0d0cda7bcf2efbbc2ff7 Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@arm.com>
Date: Wed, 29 Jan 2014 14:05:51 -0800
Subject: [PATCH] mm/readahead.c: fix do_readahead() for no readpage(s)

Commit 63d0f0a3c7e1 ("mm/readahead.c:do_readhead(): don't check for
->readpage") unintentionally made do_readahead return 0 for all valid
files regardless of whether readahead was supported, rather than the
expected -EINVAL.  This gets forwarded on to userspace, and results in
sys_readahead appearing to succeed in cases that don't make sense (e.g.
when called on pipes or sockets).  This issue is detected by the LTP
readahead01 testcase.

As the exact return value of force_page_cache_readahead is currently
never used, we can simplify it to return only 0 or -EINVAL (when
readpage or readpages is missing).  With that in place we can simply
forward on the return value of force_page_cache_readahead in
do_readahead.

This patch performs said change, restoring the expected semantics.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/readahead.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index 7cdbb44..0de2360 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -211,8 +211,6 @@ out:
 int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
 		pgoff_t offset, unsigned long nr_to_read)
 {
-	int ret = 0;
-
 	if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
 		return -EINVAL;
 
@@ -226,15 +224,13 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
 			this_chunk = nr_to_read;
 		err = __do_page_cache_readahead(mapping, filp,
 						offset, this_chunk, 0);
-		if (err < 0) {
-			ret = err;
-			break;
-		}
-		ret += err;
+		if (err < 0)
+			return err;
+
 		offset += this_chunk;
 		nr_to_read -= this_chunk;
 	}
-	return ret;
+	return 0;
 }
 
 /*
@@ -576,8 +572,7 @@ do_readahead(struct address_space *mapping, struct file *filp,
 	if (!mapping || !mapping->a_ops)
 		return -EINVAL;
 
-	force_page_cache_readahead(mapping, filp, index, nr);
-	return 0;
+	return force_page_cache_readahead(mapping, filp, index, nr);
 }
 
 SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
-- 
1.8.5.3