lkml.org 
[lkml]   [2012]   [Feb]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/2] lkdtm: use atomic_t to replace count_lock
On 02/02/2012 09:44 PM, Arnd Bergmann wrote:
> On Thursday 02 February 2012, Cong Wang wrote:
>>> In order to have an atomic here, you have to use a loop around
>>> atomic_cmpxchg, like
>>>
>>>
>>> int old, new;
>>> old = atomic_read(&count);
>>> do {
>>> new = old ? old - 1 : cpoint_count;
>>> old = cmpxchg(&count, old, new);
>>> } while (old != new);
>>>
>>> I suppose you could also just keep the spinlock and move lkdtm_do_action()
>>> outside of it?
>>
>> If we still need spinlock, I think we don't need to bother atomic_t at all.
>
> Yes, it's one or the other: If you use the cmpxchg loop, you don't need a
> spinlock and vice versa.
>

The cmpxchg loop is for comparing and assigning to 'count', but still
there is a printk() above that needs to read 'count'. Combining these
two operations means we have to use a spinlock, correct? Because there
is a chance that another process could change 'count' in between.

Thanks.


\
 
 \ /
  Last update: 2012-02-02 15:29    [W:0.626 / U:0.888 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site