On 2018-07-06 12:58:57 [+0200], To Joe Korty wrote: > On SMP + !RT migrate_disable() is still around. It is not part of spin_lock() > anymore so it has almost no users. However the futex code has a workaround for > the !in_atomic() part of migrate disable which fails because the matching > migrade_disable() is no longer part of spin_lock(). > > On !SMP + !RT migrate_disable() is reduced to barrier(). This is not optimal > because we few spots where a "preempt_disable()" statement was replaced with > "migrate_disable()". > > We also used the migration_disable counter to figure out if a sleeping lock is > acquired so RCU does not complain about schedule() during rcu_read_lock() while > a sleeping lock is held. This changed, we no longer use it, we have now a > sleeping_lock counter for the RCU purpose. > > This means we can now: > - for SMP + RT_BASE > full migration program, nothing changes here > > - for !SMP + RT_BASE > the migration counting is no longer required. It used to ensure that the task > is not migrated to another CPU and that this CPU remains online. !SMP ensures > that already. > Move it to CONFIG_SCHED_DEBUG so the counting is done for debugging purpose > only. > > - for all other cases including !RT > fallback to preempt_disable(). The only remaining users of migrate_disable() > are those which were converted from preempt_disable() and the futex > workaround which is already in the preempt_disable() section due to the > spin_lock that is held. > > Cc: stable-rt@xxxxxxxxxxxxxxx > Reported-by: joe.korty@xxxxxxxxxxxxxxxxx > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > --- > v1…v2: limit migrate_disable to RT only. Use preempt_disable() for !RT > if migrate_disable() is used. If there are no objections I would pick this up for next v4.16. Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
