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 4:46 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 08:11:58AM +0000, Liu Hui-R64343 wrote:
>>>-----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
>>
>
>I test it on my desktop against latest 3.8-rc2, can't repoduce it. :)
>
>write(1, "1\n", 2)                      = 3

Here it tells it.  

>close(1)                                = 0
>munmap(0xb779c000, 4096)                = 0
>close(2)                                = 0
>exit_group(0)                           = ?
>+++ exited with 0 +++
>
>Regards,
>Wanpeng Li
>
>>>
>>>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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>>>
>>
>


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