RE: [PATCH] mm: compaction: fix echo 1 > compact_memory return error issue

[Liu Hui-R64343 <r64343@freescale.com>]

>-----Original Message-----
>From: Wanpeng Li [mailto:liwanp@linux.vnet.ibm.com]
>Sent: Sunday, January 06, 2013 4:00 PM
>To: Liu Hui-R64343
>Cc: linux-kernel@vger.kernel.org; mgorman@suse.de; akpm@linux-
>foundation.org; riel@redhat.com; minchan@kernel.org;
>kamezawa.hiroyu@jp.fujitsu.com; linux-mm@kvack.org
>Subject: Re: [PATCH] mm: compaction: fix echo 1 > compact_memory return
>error issue
>
>On Sun, Jan 06, 2013 at 03:44:33PM +0800, Jason Liu wrote:
>
>Hi Jason,
>
>>when run the folloing command under shell, it will return error sh/$
>>echo 1 > /proc/sys/vm/compact_memory sh/$ sh: write error: Bad address
>>
>
>How can you modify the value through none privileged user since the mode
>== 0200?

I write it through privileged user(root). I'm using the GNOME_Mobile rootfs.

>
>>After strace, I found the following log:
>>...
>>write(1, "1\n", 2)               = 3
>>write(1, "", 4294967295)         = -1 EFAULT (Bad address)
>>write(2, "echo: write error: Bad address\n", 31echo: write error: Bad
>>address
>>) = 31
>>
>>This tells system return 3(COMPACT_COMPLETE) after write data to
>compact_memory.
>>
>>The fix is to make the system just return 0 instead 3(COMPACT_COMPLETE)
>>from sysctl_compaction_handler after compaction_nodes finished.
>
>What's the special scenario you are in? I couldn't figure out the similar error
>against latest 3.8-rc2, how could you reproduce it?

I'm using the BusyBox v1.20.2 () built-in shell (ash), it reproduces the issue: 100%.

root@freescale /$ sh


BusyBox v1.20.2 () built-in shell (ash)
Enter 'help' for a list of built-in commands.

Could you run strace and see the log:  strace echo 1 > /proc/sys/vm/compact_memory

>
>Regards,
>Wanpeng Li
>
>>
>>Suggested-by:David Rientjes <rientjes@google.com> Cc:Mel Gorman
>><mgorman@suse.de> Cc:Andrew Morton <akpm@linux-foundation.org>
>Cc:Rik
>>van Riel <riel@redhat.com> Cc:Minchan Kim <minchan@kernel.org>
>>Cc:KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>>Signed-off-by: Jason Liu <r64343@freescale.com>
>>---
>> mm/compaction.c |    6 ++----
>> 1 files changed, 2 insertions(+), 4 deletions(-)
>>
>>diff --git a/mm/compaction.c b/mm/compaction.c index 6b807e4..f8f5c11
>>100644
>>--- a/mm/compaction.c
>>+++ b/mm/compaction.c
>>@@ -1210,7 +1210,7 @@ static int compact_node(int nid)  }
>>
>> /* Compact all nodes in the system */
>>-static int compact_nodes(void)
>>+static void compact_nodes(void)
>> {
>> 	int nid;
>>
>>@@ -1219,8 +1219,6 @@ static int compact_nodes(void)
>>
>> 	for_each_online_node(nid)
>> 		compact_node(nid);
>>-
>>-	return COMPACT_COMPLETE;
>> }
>>
>> /* The written value is actually unused, all memory is compacted */ @@
>>-1231,7 +1229,7 @@ int sysctl_compaction_handler(struct ctl_table *table,
>int write,
>> 			void __user *buffer, size_t *length, loff_t *ppos)  {
>> 	if (write)
>>-		return compact_nodes();
>>+		compact_nodes();
>>
>> 	return 0;
>> }
>>--
>>1.7.5.4
>>
>>
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