linux-kernel - Re: [PATCH v6 04/15] memory-hotplug: remove /sys/firmware/memmap/X sysfs

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Message-ID: <50EE5C68.4030402@cn.fujitsu.com>
Date:	Thu, 10 Jan 2013 14:15:04 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	rientjes@...gle.com, len.brown@...el.com, benh@...nel.crashing.org,
	paulus@...ba.org, cl@...ux.com, minchan.kim@...il.com,
	kosaki.motohiro@...fujitsu.com, isimatu.yasuaki@...fujitsu.com,
	wujianguo@...wei.com, wency@...fujitsu.com, hpa@...or.com,
	linfeng@...fujitsu.com, laijs@...fujitsu.com, mgorman@...e.de,
	yinghai@...nel.org, glommer@...allels.com, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
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	linux-ia64@...r.kernel.org, cmetcalf@...era.com,
	sparclinux@...r.kernel.org
Subject: Re: [PATCH v6 04/15] memory-hotplug: remove /sys/firmware/memmap/X
 sysfs

Hi Andrew,

On 01/10/2013 07:19 AM, Andrew Morton wrote:
>> ...
>>
>> +	entry = firmware_map_find_entry(start, end - 1, type);
>> +	if (!entry)
>> +		return -EINVAL;
>> +
>> +	firmware_map_remove_entry(entry);
>>
>> ...
>>
>
> The above code looks racy.  After firmware_map_find_entry() does the
> spin_unlock() there is nothing to prevent a concurrent
> firmware_map_remove_entry() from removing the entry, so the kernel ends
> up calling firmware_map_remove_entry() twice against the same entry.
>
> An easy fix for this is to hold the spinlock across the entire
> lookup/remove operation.
>
>
> This problem is inherent to firmware_map_find_entry() as you have
> implemented it, so this function simply should not exist in the current
> form - no caller can use it without being buggy!  A simple fix for this
> is to remove the spin_lock()/spin_unlock() from
> firmware_map_find_entry() and add locking documentation to
> firmware_map_find_entry(), explaining that the caller must hold
> map_entries_lock and must not release that lock until processing of
> firmware_map_find_entry()'s return value has completed.

Thank you for your advice, I'll fix it soon.

Since you have merged the patch-set, do I need to resend all these
patches again, or just send a patch to fix it based on the current
one ?

Thanks. :)

>

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