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Date: Tue, 4 Jun 2019 06:53:58 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Joel Fernandes <joel@...lfernandes.org>
Cc: Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org,
Alexey Kuznetsov <kuznet@....inr.ac.ru>, Bjorn Helgaas
<bhelgaas@...gle.com>, Borislav Petkov <bp@...en8.de>, "David S. Miller"
<davem@...emloft.net>, edumazet@...gle.com, Greg Kroah-Hartman
<gregkh@...uxfoundation.org>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Josh
Triplett <josh@...htriplett.org>, keescook@...omium.org,
kernel-hardening@...ts.openwall.com, Lai Jiangshan
<jiangshanlai@...il.com>, Len Brown <lenb@...nel.org>,
linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
linux-pm@...r.kernel.org, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com>, neilb@...e.com, netdev@...r.kernel.org,
oleg@...hat.com, "Paul E. McKenney" <paulmck@...ux.ibm.com>, Pavel Machek
<pavel@....cz>, "Rafael J. Wysocki" <rjw@...ysocki.net>,
rcu@...r.kernel.org, Tejun Heo <tj@...nel.org>, Thomas Gleixner
<tglx@...utronix.de>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@...nel.org>
Subject: Re: [RFC 1/6] rcu: Add support for consolidated-RCU reader checking
On Mon, 3 Jun 2019 10:18:47 -0400
Joel Fernandes <joel@...lfernandes.org> wrote:
> On Mon, Jun 03, 2019 at 10:01:28AM +0200, Peter Zijlstra wrote:
> > On Sat, Jun 01, 2019 at 06:27:33PM -0400, Joel Fernandes (Google) wrote:
> > > +#define list_for_each_entry_rcu(pos, head, member, cond...) \
> > > + if (COUNT_VARGS(cond) != 0) { \
> > > + __list_check_rcu_cond(0, ## cond); \
> > > + } else { \
> > > + __list_check_rcu(); \
> > > + } \
> > > + for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
> > > + &pos->member != (head); \
> > > pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
> > >
> > > /**
> > > @@ -621,7 +648,12 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
> > > * the _rcu list-mutation primitives such as hlist_add_head_rcu()
> > > * as long as the traversal is guarded by rcu_read_lock().
> > > */
> > > +#define hlist_for_each_entry_rcu(pos, head, member, cond...) \
> > > + if (COUNT_VARGS(cond) != 0) { \
> > > + __list_check_rcu_cond(0, ## cond); \
> > > + } else { \
> > > + __list_check_rcu(); \
> > > + } \
> > > for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
> > > typeof(*(pos)), member); \
> > > pos; \
> >
> >
> > This breaks code like:
> >
> > if (...)
> > list_for_each_entry_rcu(...);
> >
> > as they are no longer a single statement. You'll have to frob it into
> > the initializer part of the for statement.
>
> Thanks a lot for that. I fixed it as below (diff is on top of the patch):
>
> If not for that '##' , I could have abstracted the whole if/else
> expression into its own macro and called it from list_for_each_entry_rcu() to
> keep it more clean.
>
> ---8<-----------------------
>
> diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> index b641fdd9f1a2..cc742d294bb0 100644
> --- a/include/linux/rculist.h
> +++ b/include/linux/rculist.h
> @@ -371,12 +372,15 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
> * as long as the traversal is guarded by rcu_read_lock().
> */
> #define list_for_each_entry_rcu(pos, head, member, cond...) \
> - if (COUNT_VARGS(cond) != 0) { \
> - __list_check_rcu_cond(0, ## cond); \
> - } else { \
> - __list_check_rcu(); \
> - } \
> - for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
> + for ( \
> + ({ \
> + if (COUNT_VARGS(cond) != 0) { \
> + __list_check_rcu_cond(0, ## cond); \
> + } else { \
> + __list_check_rcu_nocond(); \
> + } \
> + }), \
For easier to read I would do something like this:
#define check_rcu_list(cond) \
({ \
if (COUNT_VARGS(cond) != 0) \
__list_check_rcu_cond(0, ## cond); \
else \
__list_check_rcu_nocond(); \
})
#define list_for_each_entry_rcu(pos, head, member, cond...) \
for (check_rcu_list(cond), \
-- Steve
> + pos = list_entry_rcu((head)->next, typeof(*pos), member); \
> &pos->member != (head); \
> pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
>
> @@ -649,12 +653,15 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
> * as long as the traversal is guarded by rcu_read_lock().
> */
> #define hlist_for_each_entry_rcu(pos, head, member, cond...) \
> - if (COUNT_VARGS(cond) != 0) { \
> - __list_check_rcu_cond(0, ## cond); \
> - } else { \
> - __list_check_rcu(); \
> - } \
> - for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
> + for ( \
> + ({ \
> + if (COUNT_VARGS(cond) != 0) { \
> + __list_check_rcu_cond(0, ## cond); \
> + } else { \
> + __list_check_rcu_nocond(); \
> + } \
> + }), \
> + pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
> typeof(*(pos)), member); \
> pos; \
> pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
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