linux-kernel - [PATCH] vfs: fix find_lock_page

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Date:	Fri, 3 Apr 2009 16:22:30 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ying Han <yinghan@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu, mikew@...gle.com,
	rientjes@...gle.com, rohitseth@...gle.com, hugh@...itas.com,
	a.p.zijlstra@...llo.nl, hpa@...or.com, edwintorok@...il.com,
	lee.schermerhorn@...com, npiggin@...e.de
Subject: [PATCH] vfs: fix find_lock_page_retry() return value parsing

find_lock_page_retry() won't touch the *ppage value when returning
VM_FAULT_RETRY. This is fine except for the case

        if (VM_RandomReadHint())
                goto no_cached_page;

where the 'page' could be undefined after calling find_lock_page_retry().

Fix it by checking the VM_FAULT_RETRY case first.

Cc: Ying Han <yinghan@...gle.com>
Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
---
 mm/filemap.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- mm.orig/mm/filemap.c
+++ mm/mm/filemap.c
@@ -759,7 +759,7 @@ EXPORT_SYMBOL(find_lock_page);
  * @retry: 1 indicate caller tolerate a retry.
  *
  * If retry flag is on, and page is already locked by someone else, return
- * a hint of retry.
+ * a hint of retry and leave *ppage untouched.
  *
  * Return *ppage==NULL if page is not in pagecache. Otherwise return *ppage
  * points to the page in the pagecache with ret=VM_FAULT_RETRY indicate a
@@ -1672,10 +1672,10 @@ no_cached_page:
 
 		retry_ret = find_lock_page_retry(mapping, vmf->pgoff,
 					vma, &page, retry_flag);
+		if (retry_ret == VM_FAULT_RETRY)
+			return retry_ret;
 		if (!page)
 			goto retry_find_nopage;
-		else if (retry_ret == VM_FAULT_RETRY)
-			return retry_ret;
 		else
 			goto retry_page_update;
 	}
--
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