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Date: Mon, 3 Jun 2019 10:18:47 -0400
From: Joel Fernandes <joel@...lfernandes.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: 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,
Steven Rostedt <rostedt@...dmis.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, 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(); \
+ } \
+ }), \
+ 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(\
--
2.22.0.rc1.311.g5d7573a151-goog
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