| Message ID | 20230504012914.1797355-3-mathieu.desnoyers@efficios.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | None | expand |
Hello Mathieu, On Wed, May 3, 2023 at 9:29 PM Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > > Add missing parentheses around use of macro argument "pos" in those > patterns to ensure operator precedence behaves as expected: > > - typeof(*pos) > - pos->member > > This corrects the following usage pattern where operator precedence is > unexpected: > > LIST_HEAD(testlist); > > struct test { > struct list_head node; > int a; > }; > > // pos->member issue > void f(void) > { > struct test *t1; > struct test **t2 = &t1; > > list_for_each_entry_rcu((*t2), &testlist, node) { /* works */ > //... > } > list_for_each_entry_rcu(*t2, &testlist, node) { /* broken */ > //... > } Yeah it is not clear why anyone would ever want to use it like this. Why don't they just pass t1 to list_for_each_entry_rcu() ? I would rather it break them and they re-think their code ;). > } > > The typeof(*pos) lack of parentheses around "pos" is not an issue per se > in the specific macros modified here because "pos" is used as an lvalue, > which should prevent use of any operator causing issue. Still add the > extra parentheses for consistency. The consistency argument is valid though. I will stay neutral on this patch. ;-) thanks! - Joel > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > Cc: "Paul E. McKenney" <paulmck@kernel.org> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Frederic Weisbecker <frederic@kernel.org> > Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com> > Cc: Joel Fernandes <joel@joelfernandes.org> > Cc: Josh Triplett <josh@joshtriplett.org> > Cc: Boqun Feng <boqun.feng@gmail.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Lai Jiangshan <jiangshanlai@gmail.com> > Cc: Zqiang <qiang1.zhang@intel.com> > Cc: rcu@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > --- > include/linux/rculist.h | 28 ++++++++++++++-------------- > 1 file changed, 14 insertions(+), 14 deletions(-) > > diff --git a/include/linux/rculist.h b/include/linux/rculist.h > index d29740be4833..d27aeff5447d 100644 > --- a/include/linux/rculist.h > +++ b/include/linux/rculist.h > @@ -388,9 +388,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, > */ > #define list_for_each_entry_rcu(pos, head, member, cond...) \ > for (__list_check_rcu(dummy, ## cond, 0), \ > - pos = list_entry_rcu((head)->next, typeof(*pos), member); \ > - &pos->member != (head); \ > - pos = list_entry_rcu(pos->member.next, typeof(*pos), member)) > + pos = list_entry_rcu((head)->next, typeof(*(pos)), member);\ > + &(pos)->member != (head); \ > + pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member)) > > /** > * list_for_each_entry_srcu - iterate over rcu list of given type > @@ -407,9 +407,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, > */ > #define list_for_each_entry_srcu(pos, head, member, cond) \ > for (__list_check_srcu(cond), \ > - pos = list_entry_rcu((head)->next, typeof(*pos), member); \ > - &pos->member != (head); \ > - pos = list_entry_rcu(pos->member.next, typeof(*pos), member)) > + pos = list_entry_rcu((head)->next, typeof(*(pos)), member);\ > + &(pos)->member != (head); \ > + pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member)) > > /** > * list_entry_lockless - get the struct for this entry > @@ -441,9 +441,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, > * but never deleted. > */ > #define list_for_each_entry_lockless(pos, head, member) \ > - for (pos = list_entry_lockless((head)->next, typeof(*pos), member); \ > - &pos->member != (head); \ > - pos = list_entry_lockless(pos->member.next, typeof(*pos), member)) > + for (pos = list_entry_lockless((head)->next, typeof(*(pos)), member); \ > + &(pos)->member != (head); \ > + pos = list_entry_lockless((pos)->member.next, typeof(*(pos)), member)) > > /** > * list_for_each_entry_continue_rcu - continue iteration over list of given type > @@ -464,9 +464,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, > * position. > */ > #define list_for_each_entry_continue_rcu(pos, head, member) \ > - for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \ > - &pos->member != (head); \ > - pos = list_entry_rcu(pos->member.next, typeof(*pos), member)) > + for (pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member); \ > + &(pos)->member != (head); \ > + pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member)) > > /** > * list_for_each_entry_from_rcu - iterate over a list from current point > @@ -486,8 +486,8 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, > * after the given position. > */ > #define list_for_each_entry_from_rcu(pos, head, member) \ > - for (; &(pos)->member != (head); \ > - pos = list_entry_rcu(pos->member.next, typeof(*(pos)), member)) > + for (; &(pos)->member != (head); \ > + pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member)) > > /** > * hlist_del_rcu - deletes entry from hash list without re-initialization > -- > 2.25.1 >
On Thu, 4 May 2023 12:19:38 -0400 Joel Fernandes <joel@joelfernandes.org> wrote: > > void f(void) > > { > > struct test *t1; > > struct test **t2 = &t1; > > > > list_for_each_entry_rcu((*t2), &testlist, node) { /* works */ > > //... > > } > > list_for_each_entry_rcu(*t2, &testlist, node) { /* broken */ > > //... > > } > > Yeah it is not clear why anyone would ever want to use it like this. > Why don't they just pass t1 to list_for_each_entry_rcu() ? I would > rather it break them and they re-think their code ;). Remember interfaces should not be enforcing policy unless it's key to the way the interface works. -- Steve
> On May 5, 2023, at 10:06 AM, Steven Rostedt <rostedt@goodmis.org> wrote: > > On Thu, 4 May 2023 12:19:38 -0400 > Joel Fernandes <joel@joelfernandes.org> wrote: > >>> void f(void) >>> { >>> struct test *t1; >>> struct test **t2 = &t1; >>> >>> list_for_each_entry_rcu((*t2), &testlist, node) { /* works */ >>> //... >>> } >>> list_for_each_entry_rcu(*t2, &testlist, node) { /* broken */ >>> //... >>> } >> >> Yeah it is not clear why anyone would ever want to use it like this. >> Why don't they just pass t1 to list_for_each_entry_rcu() ? I would >> rather it break them and they re-think their code ;). > > Remember interfaces should not be enforcing policy unless it's key to the > way the interface works. Oh yeah, 100% agree. I am not particularly against this particular patch but I also dont see it as solving any problem. Feel free to Ack the patch if you feel strongly about wanting it. - Joel > > -- Steve
On Fri, 5 May 2023 10:35:39 -0400 Joel Fernandes <joel@joelfernandes.org> wrote: > >> Yeah it is not clear why anyone would ever want to use it like this. > >> Why don't they just pass t1 to list_for_each_entry_rcu() ? I would > >> rather it break them and they re-think their code ;). > > > > Remember interfaces should not be enforcing policy unless it's key to the > > way the interface works. > > Oh yeah, 100% agree. I am not particularly against this particular patch > but I also dont see it as solving any problem. Feel free to Ack the patch > if you feel strongly about wanting it. I agree that this isn't solving any real bugs, but it is a legitimate cleanup. And as someone that tends to push interfaces to their limits, I would likely be the one that hits it ;-) Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org> -- Steve
diff --git a/include/linux/rculist.h b/include/linux/rculist.h index d29740be4833..d27aeff5447d 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -388,9 +388,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, */ #define list_for_each_entry_rcu(pos, head, member, cond...) \ for (__list_check_rcu(dummy, ## cond, 0), \ - pos = list_entry_rcu((head)->next, typeof(*pos), member); \ - &pos->member != (head); \ - pos = list_entry_rcu(pos->member.next, typeof(*pos), member)) + pos = list_entry_rcu((head)->next, typeof(*(pos)), member);\ + &(pos)->member != (head); \ + pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member)) /** * list_for_each_entry_srcu - iterate over rcu list of given type @@ -407,9 +407,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, */ #define list_for_each_entry_srcu(pos, head, member, cond) \ for (__list_check_srcu(cond), \ - pos = list_entry_rcu((head)->next, typeof(*pos), member); \ - &pos->member != (head); \ - pos = list_entry_rcu(pos->member.next, typeof(*pos), member)) + pos = list_entry_rcu((head)->next, typeof(*(pos)), member);\ + &(pos)->member != (head); \ + pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member)) /** * list_entry_lockless - get the struct for this entry @@ -441,9 +441,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, * but never deleted. */ #define list_for_each_entry_lockless(pos, head, member) \ - for (pos = list_entry_lockless((head)->next, typeof(*pos), member); \ - &pos->member != (head); \ - pos = list_entry_lockless(pos->member.next, typeof(*pos), member)) + for (pos = list_entry_lockless((head)->next, typeof(*(pos)), member); \ + &(pos)->member != (head); \ + pos = list_entry_lockless((pos)->member.next, typeof(*(pos)), member)) /** * list_for_each_entry_continue_rcu - continue iteration over list of given type @@ -464,9 +464,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, * position. */ #define list_for_each_entry_continue_rcu(pos, head, member) \ - for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \ - &pos->member != (head); \ - pos = list_entry_rcu(pos->member.next, typeof(*pos), member)) + for (pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member); \ + &(pos)->member != (head); \ + pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member)) /** * list_for_each_entry_from_rcu - iterate over a list from current point @@ -486,8 +486,8 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, * after the given position. */ #define list_for_each_entry_from_rcu(pos, head, member) \ - for (; &(pos)->member != (head); \ - pos = list_entry_rcu(pos->member.next, typeof(*(pos)), member)) + for (; &(pos)->member != (head); \ + pos = list_entry_rcu((pos)->member.next, typeof(*(pos)), member)) /** * hlist_del_rcu - deletes entry from hash list without re-initialization
Add missing parentheses around use of macro argument "pos" in those patterns to ensure operator precedence behaves as expected: - typeof(*pos) - pos->member This corrects the following usage pattern where operator precedence is unexpected: LIST_HEAD(testlist); struct test { struct list_head node; int a; }; // pos->member issue void f(void) { struct test *t1; struct test **t2 = &t1; list_for_each_entry_rcu((*t2), &testlist, node) { /* works */ //... } list_for_each_entry_rcu(*t2, &testlist, node) { /* broken */ //... } } The typeof(*pos) lack of parentheses around "pos" is not an issue per se in the specific macros modified here because "pos" is used as an lvalue, which should prevent use of any operator causing issue. Still add the extra parentheses for consistency. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Zqiang <qiang1.zhang@intel.com> Cc: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- include/linux/rculist.h | 28 ++++++++++++++-------------- 1 file changed, 14 insertions(+), 14 deletions(-)