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

From: Tang Chen <[email-masked]>
Date: Thu, 10 Jan 2013 14:15:04 +0800

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. :)