* Question on comment header for for_each_domain() @ 2018-11-07 23:00 Paul E. McKenney 2018-11-08 9:21 ` Peter Zijlstra 0 siblings, 1 reply; 5+ messages in thread From: Paul E. McKenney @ 2018-11-07 23:00 UTC (permalink / raw) To: mingo, peterz; +Cc: linux-kernel Hello! The header comment for for_each_domain() talks about a call to synchronize_sched() within detach_destroy_domains(), but I am not seeing any such call. Because synchronize_sched() is now folded into synchronize_rcu(), I have a patch that edits the comment, but it looks like a larger change is needed. Or am I blind today? Thanx, Paul ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Question on comment header for for_each_domain() 2018-11-07 23:00 Question on comment header for for_each_domain() Paul E. McKenney @ 2018-11-08 9:21 ` Peter Zijlstra 2018-11-08 15:31 ` Paul E. McKenney 0 siblings, 1 reply; 5+ messages in thread From: Peter Zijlstra @ 2018-11-08 9:21 UTC (permalink / raw) To: Paul E. McKenney; +Cc: mingo, linux-kernel On Wed, Nov 07, 2018 at 03:00:02PM -0800, Paul E. McKenney wrote: > Hello! > > The header comment for for_each_domain() talks about a call to > synchronize_sched() within detach_destroy_domains(), but I am not > seeing any such call. Because synchronize_sched() is now folded into > synchronize_rcu(), I have a patch that edits the comment, but it looks > like a larger change is needed. > > Or am I blind today? I think you're quite right and that comment is a wee bit stale. The sched domain tree is indeed protected by regular RCU (not RCU-sched as the comment seems to imply) and this is per destroy_sched_domains() using call_rcu(). And most (I didn't look at all) uses for the sched-domain tree do indeed employ rcu_read_lock(). ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Question on comment header for for_each_domain() 2018-11-08 9:21 ` Peter Zijlstra @ 2018-11-08 15:31 ` Paul E. McKenney 2018-11-08 15:35 ` Peter Zijlstra 0 siblings, 1 reply; 5+ messages in thread From: Paul E. McKenney @ 2018-11-08 15:31 UTC (permalink / raw) To: Peter Zijlstra; +Cc: mingo, linux-kernel On Thu, Nov 08, 2018 at 10:21:51AM +0100, Peter Zijlstra wrote: > On Wed, Nov 07, 2018 at 03:00:02PM -0800, Paul E. McKenney wrote: > > Hello! > > > > The header comment for for_each_domain() talks about a call to > > synchronize_sched() within detach_destroy_domains(), but I am not > > seeing any such call. Because synchronize_sched() is now folded into > > synchronize_rcu(), I have a patch that edits the comment, but it looks > > like a larger change is needed. > > > > Or am I blind today? > > I think you're quite right and that comment is a wee bit stale. > > The sched domain tree is indeed protected by regular RCU (not RCU-sched > as the comment seems to imply) and this is per destroy_sched_domains() > using call_rcu(). > > And most (I didn't look at all) uses for the sched-domain tree do indeed > employ rcu_read_lock(). Ah, thank you for the info! Would this patch do the trick? Thanx, Paul ------------------------------------------------------------------------ commit 4182d416309b11d16e882ab637ab11cecef0bddc Author: Paul E. McKenney <paulmck@linux.ibm.com> Date: Tue Nov 6 19:10:53 2018 -0800 sched: Replace call_rcu_sched() with call_rcu() Now that call_rcu()'s callback is not invoked until after all preempt-disable regions of code have completed (in addition to explicitly marked RCU read-side critical sections), call_rcu() can be used in place of call_rcu_sched(). This commit therefore makes that change. While in the area, this commit also updates an outdated header comment for for_each_domain(). Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 618577fc9aa8..00b91d16af9f 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1237,7 +1237,7 @@ extern void sched_ttwu_pending(void); /* * The domain tree (rq->sd) is protected by RCU's quiescent state transition. - * See detach_destroy_domains: synchronize_sched for details. + * See destroy_sched_domains: call_rcu for details. * * The domain tree of any CPU may only be accessed from within * preempt-disabled sections. diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 8d7f15ba5916..04d458faf2c1 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -248,7 +248,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd) raw_spin_unlock_irqrestore(&rq->lock, flags); if (old_rd) - call_rcu_sched(&old_rd->rcu, free_rootdomain); + call_rcu(&old_rd->rcu, free_rootdomain); } void sched_get_rd(struct root_domain *rd) @@ -261,7 +261,7 @@ void sched_put_rd(struct root_domain *rd) if (!atomic_dec_and_test(&rd->refcount)) return; - call_rcu_sched(&rd->rcu, free_rootdomain); + call_rcu(&rd->rcu, free_rootdomain); } static int init_rootdomain(struct root_domain *rd) ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: Question on comment header for for_each_domain() 2018-11-08 15:31 ` Paul E. McKenney @ 2018-11-08 15:35 ` Peter Zijlstra 2018-11-08 16:11 ` Paul E. McKenney 0 siblings, 1 reply; 5+ messages in thread From: Peter Zijlstra @ 2018-11-08 15:35 UTC (permalink / raw) To: Paul E. McKenney; +Cc: mingo, linux-kernel On Thu, Nov 08, 2018 at 07:31:09AM -0800, Paul E. McKenney wrote: > On Thu, Nov 08, 2018 at 10:21:51AM +0100, Peter Zijlstra wrote: > > On Wed, Nov 07, 2018 at 03:00:02PM -0800, Paul E. McKenney wrote: > > > Hello! > > > > > > The header comment for for_each_domain() talks about a call to > > > synchronize_sched() within detach_destroy_domains(), but I am not > > > seeing any such call. Because synchronize_sched() is now folded into > > > synchronize_rcu(), I have a patch that edits the comment, but it looks > > > like a larger change is needed. > > > > > > Or am I blind today? > > > > I think you're quite right and that comment is a wee bit stale. > > > > The sched domain tree is indeed protected by regular RCU (not RCU-sched > > as the comment seems to imply) and this is per destroy_sched_domains() > > using call_rcu(). > > > > And most (I didn't look at all) uses for the sched-domain tree do indeed > > employ rcu_read_lock(). > > Ah, thank you for the info! Would this patch do the trick? > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 618577fc9aa8..00b91d16af9f 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1237,7 +1237,7 @@ extern void sched_ttwu_pending(void); > > /* > * The domain tree (rq->sd) is protected by RCU's quiescent state transition. > - * See detach_destroy_domains: synchronize_sched for details. > + * See destroy_sched_domains: call_rcu for details. > * > * The domain tree of any CPU may only be accessed from within > * preempt-disabled sections. > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > index 8d7f15ba5916..04d458faf2c1 100644 > --- a/kernel/sched/topology.c > +++ b/kernel/sched/topology.c > @@ -248,7 +248,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd) > raw_spin_unlock_irqrestore(&rq->lock, flags); > > if (old_rd) > - call_rcu_sched(&old_rd->rcu, free_rootdomain); > + call_rcu(&old_rd->rcu, free_rootdomain); > } > > void sched_get_rd(struct root_domain *rd) > @@ -261,7 +261,7 @@ void sched_put_rd(struct root_domain *rd) > if (!atomic_dec_and_test(&rd->refcount)) > return; > > - call_rcu_sched(&rd->rcu, free_rootdomain); > + call_rcu(&rd->rcu, free_rootdomain); > } > > static int init_rootdomain(struct root_domain *rd) > Argh, that is the rootdomain, not the regular sched-domain tree. Now I'll have to go audit that stuff again. ISTR there being slightly different rules for rootdomain, and with a reason. Can we hold onto this until after LPC? ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Question on comment header for for_each_domain() 2018-11-08 15:35 ` Peter Zijlstra @ 2018-11-08 16:11 ` Paul E. McKenney 0 siblings, 0 replies; 5+ messages in thread From: Paul E. McKenney @ 2018-11-08 16:11 UTC (permalink / raw) To: Peter Zijlstra; +Cc: mingo, linux-kernel On Thu, Nov 08, 2018 at 04:35:40PM +0100, Peter Zijlstra wrote: > On Thu, Nov 08, 2018 at 07:31:09AM -0800, Paul E. McKenney wrote: > > On Thu, Nov 08, 2018 at 10:21:51AM +0100, Peter Zijlstra wrote: > > > On Wed, Nov 07, 2018 at 03:00:02PM -0800, Paul E. McKenney wrote: > > > > Hello! > > > > > > > > The header comment for for_each_domain() talks about a call to > > > > synchronize_sched() within detach_destroy_domains(), but I am not > > > > seeing any such call. Because synchronize_sched() is now folded into > > > > synchronize_rcu(), I have a patch that edits the comment, but it looks > > > > like a larger change is needed. > > > > > > > > Or am I blind today? > > > > > > I think you're quite right and that comment is a wee bit stale. > > > > > > The sched domain tree is indeed protected by regular RCU (not RCU-sched > > > as the comment seems to imply) and this is per destroy_sched_domains() > > > using call_rcu(). > > > > > > And most (I didn't look at all) uses for the sched-domain tree do indeed > > > employ rcu_read_lock(). > > > > Ah, thank you for the info! Would this patch do the trick? > > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > > index 618577fc9aa8..00b91d16af9f 100644 > > --- a/kernel/sched/sched.h > > +++ b/kernel/sched/sched.h > > @@ -1237,7 +1237,7 @@ extern void sched_ttwu_pending(void); > > > > /* > > * The domain tree (rq->sd) is protected by RCU's quiescent state transition. > > - * See detach_destroy_domains: synchronize_sched for details. > > + * See destroy_sched_domains: call_rcu for details. > > * > > * The domain tree of any CPU may only be accessed from within > > * preempt-disabled sections. > > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > > index 8d7f15ba5916..04d458faf2c1 100644 > > --- a/kernel/sched/topology.c > > +++ b/kernel/sched/topology.c > > @@ -248,7 +248,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd) > > raw_spin_unlock_irqrestore(&rq->lock, flags); > > > > if (old_rd) > > - call_rcu_sched(&old_rd->rcu, free_rootdomain); > > + call_rcu(&old_rd->rcu, free_rootdomain); > > } > > > > void sched_get_rd(struct root_domain *rd) > > @@ -261,7 +261,7 @@ void sched_put_rd(struct root_domain *rd) > > if (!atomic_dec_and_test(&rd->refcount)) > > return; > > > > - call_rcu_sched(&rd->rcu, free_rootdomain); > > + call_rcu(&rd->rcu, free_rootdomain); > > } > > > > static int init_rootdomain(struct root_domain *rd) > > Argh, that is the rootdomain, not the regular sched-domain tree. Now > I'll have to go audit that stuff again. > > ISTR there being slightly different rules for rootdomain, and with a > reason. > > Can we hold onto this until after LPC? This patch isn't going anywhere irrevocable until -rc5 anyway, so no problem. ;-) Thanx, Paul ^ permalink raw reply [flat|nested] 5+ messages in thread
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