[PATCH] vfs: fix find_lock_page_retry() return value parsing

[Wu Fengguang]

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@xxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 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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