lkml.org 
[lkml]   [2013]   [Sep]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines and locking code into its own file
From
On Fri, Sep 27, 2013 at 12:38 PM, Tim Chen <tim.c.chen@linux.intel.com> wrote:

> BTW, is the above memory barrier necessary? It seems like the xchg
> instruction already provided a memory barrier.
>
> Now if we made the changes that Jason suggested:
>
>
> /* Init node */
> - node->locked = 0;
> node->next = NULL;
>
> prev = xchg(lock, node);
> if (likely(prev == NULL)) {
> /* Lock acquired */
> - node->locked = 1;
> return;
> }
> + node->locked = 0;
> ACCESS_ONCE(prev->next) = node;
> smp_wmb();
>
> We are probably still okay as other cpus do not read the value of
> node->locked, which is a local variable.

Similarly, I was wondering if we should also move smp_wmb() so that it
is before the ACCESS_ONCE(prev->next) = node and after the
node->locked = 0. Would we want to guarantee that the node->locked
gets set before it is added to the linked list where a previous thread
calling mcs_spin_unlock() would potentially modify node->locked?


\
 
 \ /
  Last update: 2013-09-27 22:41    [W:0.094 / U:18.452 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site