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Date: Sun, 4 Mar 2012 13:17:25 +0800
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Subject: [PATCH] mm: shmem: unlock valid page
From: Hillf Danton <dhillf@gmail.com>
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Sender: owner-linux-mm@kvack.org
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To: Linux-MM <linux-mm@kvack.org>
Cc: Hugh Dickins <hughd@google.com>, Andrew Morton <akpm@linux-foundation.org>, LKML <linux-kernel@vger.kernel.org>, Hillf Danton <dhillf@gmail.com>

In shmem_read_mapping_page_gfp() page is unlocked if no error returned,
so the unlocked page has to valid.

To guarantee that validity, when getting page, success result is feed
back to caller only when page is valid.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
---

--- a/mm/shmem.c	Sun Mar  4 12:17:42 2012
+++ b/mm/shmem.c	Sun Mar  4 12:26:56 2012
@@ -889,13 +889,13 @@ repeat:
 		goto failed;
 	}

-	if (page || (sgp == SGP_READ && !swap.val)) {
+	if (page) {
 		/*
 		 * Once we can get the page lock, it must be uptodate:
 		 * if there were an error in reading back from swap,
 		 * the page would not be inserted into the filecache.
 		 */
-		BUG_ON(page && !PageUptodate(page));
+		BUG_ON(!PageUptodate(page));
 		*pagep = page;
 		return 0;
 	}
--

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