lkml.org 
[lkml]   [2012]   [Oct]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: Process Hang in __read_seqcount_begin
From
On Mon, Oct 22, 2012 at 10:01 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> This looks like a corruption of s->sequence, and is value is odd, even
> if no writer is alive.
>
> Does local_bh_disable() disables preemption on RT ?

Hmmm....

With PREEMPT_RT_FULL defined (as we have):

void local_bh_disable(void)
{
migrate_disable();
current->softirq_nestcnt++;
}

And the RT patches add the following:

#ifdef CONFIG_PREEMPT_RT_FULL
# define preempt_disable_rt() preempt_disable()
# define preempt_enable_rt() preempt_enable()
# define preempt_disable_nort() do { } while (0)
# define preempt_enable_nort() do { } while (0)
# ifdef CONFIG_SMP
extern void migrate_disable(void);
extern void migrate_enable(void);
# else /* CONFIG_SMP */
# define migrate_disable() do { } while (0)
# define migrate_enable() do { } while (0)
# endif /* CONFIG_SMP */
#else
# define preempt_disable_rt() do { } while (0)
# define preempt_enable_rt() do { } while (0)
# define preempt_disable_nort() preempt_disable()
# define preempt_enable_nort() preempt_enable()
# define migrate_disable() preempt_disable()
# define migrate_enable() preempt_enable()
#endif

And since we are not SMP, local_bh_disable() essentially does nothing.
These definitions are consistent across all the RT patches, up to
3.6.2-rt4 (as far as I can tell).

Now, is preemption required to be disabled in non-SMP systems?


\
 
 \ /
  Last update: 2012-10-22 20:01    [W:0.242 / U:0.728 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site