linux-kernel - Re: [RFC, PATCH] kernel/rcu: add kfree

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20090103234637.GD6958@linux.vnet.ibm.com>
Date:	Sat, 3 Jan 2009 15:46:37 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Manfred Spraul <manfred@...orfullife.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	laijs@...fujitsu.com
Subject: Re: [RFC, PATCH] kernel/rcu: add kfree_rcu

On Sat, Jan 03, 2009 at 03:59:40PM +0100, Manfred Spraul wrote:
> Paul E. McKenney wrote:
>> I would suggest instead using the bottom bit to differentiate between
>> these two cases, especially given that your approach makes it impossible
>> for callback processing to notice a NULL function pointer.  In addition,
>> this approach would allow different types of allocators to be specified
>> should this later prove to be helpful.  You should not have to shift the
>> offset because the rcu_head offset should always be a multiple of four
>> (or eight on 64-bit architectures).
>>   
> We must be careful: rcu_head might be always aligned, but are function 
> pointers always aligned?
> The x86 hardware allows arbitrary function pointers, I'm not sure what gcc 
> would do if '--falign-functions=0' is used.
> Are there other codepaths that assume that the lowest bit of a function 
> pointer is never set?

Good point.  I guess that we will have to worry about expandability when
and if the need arises.  I see a couple of ways of doing it, but they
are pretty ugly...

>> And we really are running into bugs that are detected by RCU's seeing a
>> null function pointer in the rcu_head structure at callback-invocation
>> time.  So, whatever encoding you choose, please leave a function-pointer
>> value of zero as an invalid value!
>>   
> Ok.
>
>>> --- a/kernel/rcutree.c
>>> +++ b/kernel/rcutree.c
>>> @@ -901,7 +901,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
>>>  	while (list) {
>>>  		next = list->next;
>>>  		prefetch(next);
>>> -		list->func(list);
>>> +		rcu_docallback(list);
>>>     
>>
>> Good, you got all three of them!  ;-)
>>
>>   
> The patch was tested against rcutree ;-)

;-)

							Thanx, Paul
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/