On Thu, 30 Apr 2015 20:07:21 +0200
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Thu, Apr 30, 2015 at 12:33:03PM -0400, Steven Rostedt wrote:
> > diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> > index 51435dbce9c4..dbaa1ce3f308 100644
> > --- a/fs/xfs/xfs_mount.c
> > +++ b/fs/xfs/xfs_mount.c
> > @@ -1660,6 +1660,12 @@ xfs_icsb_lock_all_counters(
> > xfs_icsb_cnts_t *cntp;
> > int i;
> >
> > + /*
> > + * In PREEMPT_RT, preemption is not disabled here, and it
> > + * must be to take the xfs_icsb_lock_cntr.
> > + */
> > + preempt_disable_rt();
> > +
> > for_each_online_cpu(i) {
> > cntp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, i);
> > xfs_icsb_lock_cntr(cntp);
> > @@ -1677,6 +1683,8 @@ xfs_icsb_unlock_all_counters(
> > cntp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, i);
> > xfs_icsb_unlock_cntr(cntp);
> > }
> > +
> > + preempt_enable_rt();
> > }
>
> The irony, this is distinctly non deterministic code you're putting
> under a RT specific preempt_disable ;-)
I know :-(
Unfortunately, a RT behaving fix would be much more invasive and would
probably require the help of the xfs folks. For now, this just prevents
a live lock that can happen and halt the system, where it becomes
deterministic catastrophe.
-- Steve
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