2012-08-21 06:44:00

by Wen Congyang

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

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 <[email protected]>
---
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

2012-08-21 07:37:22

by Minchan Kim

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

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 <[email protected]>
Reviewed-by: Minchan Kim <[email protected]>

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