[PATCH] memory hotplug: reset pgdat->kswapd to NULL if creating kernel thread fails

[PATCH] memory hotplug: reset pgdat->kswapd to NULL if creating kernel thread fails

[Wen Congyang]

If kthread_run() fails, pgdat->kswapd contains errno. When we stop
this thread, we only check whether pgdat->kswapd is NULL and access
it. If it contains errno, it will cause page fault. Reset pgdat->kswapd
to NULL when creating kernel thread fails can avoid this problem.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
---
 mm/vmscan.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 347b3ff..1e8e2aa 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2953,6 +2953,7 @@ int kswapd_run(int nid)
 		/* failure at boot is fatal */
 		BUG_ON(system_state == SYSTEM_BOOTING);
 		printk("Failed to start kswapd on node %d\n",nid);
+		pgdat->kswapd = NULL;
 		ret = -1;
 	}
 	return ret;
-- 
1.7.1

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [PATCH] memory hotplug: reset pgdat->kswapd to NULL if creating kernel thread fails

[Minchan Kim]

On Tue, Aug 21, 2012 at 02:31:19PM +0800, Wen Congyang wrote:
> If kthread_run() fails, pgdat->kswapd contains errno. When we stop
> this thread, we only check whether pgdat->kswapd is NULL and access
> it. If it contains errno, it will cause page fault. Reset pgdat->kswapd
> to NULL when creating kernel thread fails can avoid this problem.
> 
> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Reviewed-by: Minchan Kim <minchan@kernel.org>

Nitpick: Why doesn't online_pages check kswapd_run's return value?
         I hope memory-hotplug can handle this error rightly without
         relying on this patch in the future.

-- 
Kind regards,
Minchan Kim

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>