linux-kernel - [patch 04/11 -mmotm] oom: fix possible android low memory killer NULL pointer

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Message-ID: <alpine.DEB.2.00.0905101500460.18804@chino.kir.corp.google.com>
Date:	Sun, 10 May 2009 15:07:14 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Greg Kroah-Hartman <gregkh@...e.de>, Nick Piggin <npiggin@...e.de>,
	Mel Gorman <mel@....ul.ie>,
	Peter Ziljstra <a.p.ziljstra@...llo.nl>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	San Mehat <san@...roid.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	linux-kernel@...r.kernel.org
Subject: [patch 04/11 -mmotm] oom: fix possible android low memory killer
 NULL pointer

get_mm_rss() atomically dereferences the actual without checking for a
NULL pointer, which is possible since task_lock() is not held.

Cc: San Mehat <san@...roid.com>
Signed-off-by: David Rientjes <rientjes@...gle.com>
---
 drivers/staging/android/lowmemorykiller.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -92,12 +92,18 @@ static int lowmem_shrink(int nr_to_scan, gfp_t gfp_mask)
 	for_each_process(p) {
 		int oom_adj;
 
-		if (!p->mm)
+		task_lock(p);
+		if (!p->mm) {
+			task_unlock(p);
 			continue;
+		}
 		oom_adj = p->oomkilladj;
-		if (oom_adj < min_adj)
+		if (oom_adj < min_adj) {
+			task_unlock(p);
 			continue;
+		}
 		tasksize = get_mm_rss(p->mm);
+		task_unlock(p);
 		if (tasksize <= 0)
 			continue;
 		if (selected) {
--
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