linux-kernel - [PATCH 2/X] uprobes: write_opcode() needs put_page(new

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Date:	Sat, 15 Oct 2011 21:00:57 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 2/X] uprobes: write_opcode() needs put_page(new_page)
	unconditionally

Every write_opcode()->__replace_page() leaks the new page on success.

We have the reference after alloc_page_vma(), then __replace_page()
does another get_page() for the new mapping, we need put_page(new_page)
in any case.

Alternatively we could remove __replace_page()->get_page() but it is
better to change write_opcode(). This way it is simpler to unify the
code with ksm.c:replace_page() and we can simplify the error handling
in write_opcode(), the patch simply adds a single page_cache_release()
under "unlock_out" label.
---
 kernel/uprobes.c |   15 +++++----------
 1 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/kernel/uprobes.c b/kernel/uprobes.c
index 52b20c8..fd9c8e3 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -193,15 +193,12 @@ static int write_opcode(struct task_struct *tsk, struct uprobe * uprobe,
 	if (vaddr != (unsigned long) addr)
 		goto put_out;
 
-	/* Allocate a page */
+	ret = -ENOMEM;
 	new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);
-	if (!new_page) {
-		ret = -ENOMEM;
+	if (!new_page)
 		goto put_out;
-	}
 
 	__SetPageUptodate(new_page);
-
 	/*
 	 * lock page will serialize against do_wp_page()'s
 	 * PageAnon() handling
@@ -220,18 +217,16 @@ static int write_opcode(struct task_struct *tsk, struct uprobe * uprobe,
 	kunmap_atomic(vaddr_old);
 
 	ret = anon_vma_prepare(vma);
-	if (ret) {
-		page_cache_release(new_page);
+	if (ret)
 		goto unlock_out;
-	}
 
 	lock_page(new_page);
 	ret = __replace_page(vma, old_page, new_page);
 	unlock_page(new_page);
-	if (ret != 0)
-		page_cache_release(new_page);
+
 unlock_out:
 	unlock_page(old_page);
+	page_cache_release(new_page);
 
 put_out:
 	put_page(old_page); /* we did a get_page in the beginning */
-- 
1.5.5.1


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