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Message-ID: <alpine.DEB.2.00.1101070922100.3014@router.home>
Date: Fri, 7 Jan 2011 09:22:46 -0600 (CST)
From: Christoph Lameter <cl@...ux.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc: David Rientjes <rientjes@...gle.com>,
Pekka Enberg <penberg@...nel.org>,
Bart Van Assche <bvanassche@....org>,
linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] slub: Fix sysfs circular locking dependency
On Fri, 7 Jan 2011, KAMEZAWA Hiroyuki wrote:
> But, nice catch. I think MEM_GOING_ONLINE, MEM_ONLINE should be done under
> lock_memory_hotplug. So, could you update your patch and modify online_pages() ?
>
> IIUC, online_pages() is an user interface function and there will be no downside
> to insert lock there. online_pages() should be serialized.
Subject: slub: Avoid use of slub_lock in show_slab_objects()
The purpose of the locking is to prevent removal and additions
of nodes when statistics are gathered for a slab cache. So we
need to avoid racing with memory hotplug functionality.
It is enough to take the memory hotplug locks there instead
of the slub_lock.
online_pages() does not acquire the memory_hotplug lock. So
add the missing locking there.
Signed-off-by: Christoph Lameter <cl@...ux.com>
---
mm/memory_hotplug.c | 17 +++++++++++------
mm/slub.c | 4 ++--
2 files changed, 13 insertions(+), 8 deletions(-)
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2011-01-07 09:17:35.000000000 -0600
+++ linux-2.6/mm/slub.c 2011-01-07 09:17:38.000000000 -0600
@@ -3821,7 +3821,7 @@ static ssize_t show_slab_objects(struct
}
}
- down_read(&slub_lock);
+ lock_memory_hotplug();
#ifdef CONFIG_SLUB_DEBUG
if (flags & SO_ALL) {
for_each_node_state(node, N_NORMAL_MEMORY) {
@@ -3862,7 +3862,7 @@ static ssize_t show_slab_objects(struct
x += sprintf(buf + x, " N%d=%lu",
node, nodes[node]);
#endif
- up_read(&slub_lock);
+ unlock_memory_hotplug();
kfree(nodes);
return x + sprintf(buf + x, "\n");
}
Index: linux-2.6/mm/memory_hotplug.c
===================================================================
--- linux-2.6.orig/mm/memory_hotplug.c 2011-01-07 09:17:59.000000000 -0600
+++ linux-2.6/mm/memory_hotplug.c 2011-01-07 09:20:07.000000000 -0600
@@ -415,12 +415,12 @@ int online_pages(unsigned long pfn, unsi
if (node_present_pages(nid) == 0)
arg.status_change_nid = nid;
+ lock_memory_hotplug();
ret = memory_notify(MEM_GOING_ONLINE, &arg);
ret = notifier_to_errno(ret);
- if (ret) {
- memory_notify(MEM_CANCEL_ONLINE, &arg);
- return ret;
- }
+ if (ret)
+ goto cancel;
+
/*
* This doesn't need a lock to do pfn_to_page().
* The section can't be removed here because of the
@@ -442,8 +442,7 @@ int online_pages(unsigned long pfn, unsi
mutex_unlock(&zonelists_mutex);
printk(KERN_DEBUG "online_pages %lx at %lx failed\n",
nr_pages, pfn);
- memory_notify(MEM_CANCEL_ONLINE, &arg);
- return ret;
+ goto cancel;
}
zone->present_pages += onlined_pages;
@@ -468,7 +467,13 @@ int online_pages(unsigned long pfn, unsi
if (onlined_pages)
memory_notify(MEM_ONLINE, &arg);
+ unlock_memory_hotplug();
return 0;
+
+cancel:
+ memory_notify(MEM_CANCEL_ONLINE, &arg);
+ unlock_memory_hotplug();
+ return ret;
}
#endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
--
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