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Message-ID: <20190604174802.GB228607@google.com>
Date: Tue, 4 Jun 2019 13:48:02 -0400
From: Joel Fernandes <joel@...lfernandes.org>
To: Steven Rostedt <rostedt@...dmis.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 Tue, Jun 04, 2019 at 06:53:58AM -0400, Steven Rostedt wrote:
> 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), \
Yes, already doing it this way as I replied to Peter here:
https://lore.kernel.org/patchwork/patch/1082846/#1278489
Thanks!
- Joel
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