lkml.org 
[lkml]   [2012]   [Mar]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/2] module: use rcu to protect module list read
On 03/10/2012 11:25 PM, Eric Dumazet wrote:
> Le samedi 10 mars 2012 à 22:20 +0800, Cong Wang a écrit :
>> Now the read of module list is protected by preempt disable + *_rcu
>> list operations, this is odd, as RCU read lock should be able to
>> protect it directly. This patch makes the read of module list
>> protected by RCU read lock and the write still protected by
>> module_mutex.
>>
>
> Problem is that your patch does more than that.
>
> In set_all_modules_text_rw() and set_all_modules_text_ro() you removed
> the mutex in favor of rcu_read_lock()

Yeah, I was wrong, set_all_modules_text_rw() and
set_all_modules_text_ro() mean to block module add/del, it is correct to
use module_mutex.

>
> Also, module code uses synchronize_sched(), not synchronize_rcu()

Stupid me, I totally missed this, should use rcu_read_lock_sched()...

>
> Take a look at Documentation/RCU/whatisRCU.txt and see that
> preempt_disable() / preempt_enable() are documented as a right protect
> code, in line 333.
>
> You added races in /proc/modules as well.

Yeah, that list iteration is not protected by rcu yet.

>
> So I would say your patch is not needed at all : module code already
> uses RCU.
>
> What particular problem do you have with current code ?

preempt_disable() + list_*_rcu() looks a little weird for me,
rcu_read_lock_sched() + list_*_rcu() is better, although they are
functionally equal.

I will send out a new version.

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

\
 
 \ /
  Last update: 2012-03-11 11:57    [W:0.065 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site