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Date: Wed, 11 Feb 2015 12:39:47 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
        Tang Chen <tangchen@cn.fujitsu.com>, Vlastimil Babka <vbabka@suse.cz>,
        David Rientjes <rientjes@google.com>,
        Fabian Frederick <fabf@skynet.be>,
        Zhang Zhen <zhenzhang.zhang@huawei.com>,
        Vladimir Davydov <vdavydov@parallels.com>,
        Wang Nan <wangnan0@huawei.com>, linux-kernel@vger.kernel.org,
        devel@linuxdriverproject.org, linux-mm@kvack.org,
        "Rafael J. Wysocki" <rjw@sisk.pl>
Subject: Re: [PATCH 1/3] driver core: export
 lock_device_hotplug/unlock_device_hotplug
Message-Id: <20150211123947.3318933f2aca54e11324b088@linux-foundation.org>
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On Wed, 11 Feb 2015 16:44:20 +0100 Vitaly Kuznetsov <vkuznets@redhat.com> wrote:

> add_memory() is supposed to be run with device_hotplug_lock grabbed, otherwise
> it can race with e.g. device_online(). Allow external modules (hv_balloon for
> now) to lock device hotplug.
> 
> ...
>
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -55,11 +55,13 @@ void lock_device_hotplug(void)
>  {
>  	mutex_lock(&device_hotplug_lock);
>  }
> +EXPORT_SYMBOL_GPL(lock_device_hotplug);
>  
>  void unlock_device_hotplug(void)
>  {
>  	mutex_unlock(&device_hotplug_lock);
>  }
> +EXPORT_SYMBOL_GPL(unlock_device_hotplug);
>  
>  int lock_device_hotplug_sysfs(void)
>  {

It's kinda crazy that lock_device_hotplug_sysfs() didn't get any
documentation.  I suggest adding this while you're in there:


--- a/drivers/base/core.c~a
+++ a/drivers/base/core.c
@@ -61,6 +61,9 @@ void unlock_device_hotplug(void)
 	mutex_unlock(&device_hotplug_lock);
 }
 
+/*
+ * "git show 5e33bc4165f3ed" for details
+ */
 int lock_device_hotplug_sysfs(void)
 {
 	if (mutex_trylock(&device_hotplug_lock))

which is a bit lazy but whatev.

I'll assume that Greg (or Rafael?) will be processing this patchset.