Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Thu, 4 May 2023 17:28:52 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [RFC PATCH] rcu: rcupdate.h: Add missing parentheses around macro pointer dereference |
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On Wed, May 03, 2023 at 06:06:40PM -0400, Steven Rostedt wrote: > On Wed, 3 May 2023 16:32:36 -0400 > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > > > linux/rcupdate.h macros use the *p parameter without parentheses, e.g.: > > > > typeof(*p) > > > > rather than > > > > typeof(*(p)) > > > > The following test-case shows how it can generate confusion due to C > > operator precedence being reversed compared to the expectations: > > > > #define m(p) \ > > do { \ > > __typeof__(*p) v = 0; \ > > } while (0) > > > > void fct(unsigned long long *p1) > > { > > m(p1 + 1); /* works */ > > m(1 + p1); /* broken */ > > } > > > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > > Cc: "Paul E. McKenney" <paulmck@kernel.org> > > 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> > > --- > > include/linux/rcupdate.h | 18 +++++++++--------- > > 1 file changed, 9 insertions(+), 9 deletions(-) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index dcd2cf1e8326..1565012fa47f 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -430,16 +430,16 @@ static inline void rcu_preempt_sleep_check(void) { } > > > > #ifdef __CHECKER__ > > #define rcu_check_sparse(p, space) \ > > - ((void)(((typeof(*p) space *)p) == p)) > > + ((void)(((typeof(*(p)) space *)p) == p)) > > Hmm, should we have that be: > ((void)(((typeof(*(p)) space *)(p)) == (p))) > > In case of the 1 + p1, which would end up as: > > ((void)(((typeof(*(1 + p1)) __rcu *)1 + p1 == 1 + p1; > > I don't know how that __rcu get's passed around via the + statement there, > so it may be fine. May not even make sense to have that. But I like to > error on more parenthesis. ;-) > > The rest looks fine. > > Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Thank you all! I applied Steve's suggested change with attribution as shown below. Please let me know if I messed anything up.
Thanx, Paul
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commit d3d734216c88fb7c13205dc62178ff5011da415b Author: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Date: Wed May 3 16:32:36 2023 -0400
rcu: Add missing parentheses around rcu_dereference() "p" parameter linux/rcupdate.h macros use the *p parameter without parentheses, e.g.: typeof(*p) rather than typeof(*(p)) The following test-case shows how it can generate confusion due to C operator precedence being reversed compared to the expectations: #define m(p) \ do { \ __typeof__(*p) v = 0; \ } while (0) void fct(unsigned long long *p1) { m(p1 + 1); /* works */ m(1 + p1); /* broken */ } [ paulmck: Apply Steve Rostedt additional () feedback. ] Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: "Paul E. McKenney" <paulmck@kernel.org> 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> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index ddd42efc6224..cb938a89a923 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -405,16 +405,16 @@ static inline void rcu_preempt_sleep_check(void) { } #ifdef __CHECKER__ #define rcu_check_sparse(p, space) \ - ((void)(((typeof(*p) space *)p) == p)) + ((void)(((typeof(*(p)) space *)(p)) == (p))) #else /* #ifdef __CHECKER__ */ #define rcu_check_sparse(p, space) #endif /* #else #ifdef __CHECKER__ */ #define __unrcu_pointer(p, local) \ ({ \ - typeof(*p) *local = (typeof(*p) *__force)(p); \ + typeof(*(p)) *local = (typeof(*(p)) *__force)(p); \ rcu_check_sparse(p, __rcu); \ - ((typeof(*p) __force __kernel *)(local)); \ + ((typeof(*(p)) __force __kernel *)(local)); \ }) /** * unrcu_pointer - mark a pointer as not being RCU protected @@ -427,29 +427,29 @@ static inline void rcu_preempt_sleep_check(void) { } #define __rcu_access_pointer(p, local, space) \ ({ \ - typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ + typeof(*(p)) *local = (typeof(*(p)) *__force)READ_ONCE(p); \ rcu_check_sparse(p, space); \ - ((typeof(*p) __force __kernel *)(local)); \ + ((typeof(*(p)) __force __kernel *)(local)); \ }) #define __rcu_dereference_check(p, local, c, space) \ ({ \ /* Dependency order vs. p above. */ \ - typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ + typeof(*(p)) *local = (typeof(*(p)) *__force)READ_ONCE(p); \ RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ rcu_check_sparse(p, space); \ - ((typeof(*p) __force __kernel *)(local)); \ + ((typeof(*(p)) __force __kernel *)(local)); \ }) #define __rcu_dereference_protected(p, local, c, space) \ ({ \ RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ rcu_check_sparse(p, space); \ - ((typeof(*p) __force __kernel *)(p)); \ + ((typeof(*(p)) __force __kernel *)(p)); \ }) #define __rcu_dereference_raw(p, local) \ ({ \ /* Dependency order vs. p above. */ \ typeof(p) local = READ_ONCE(p); \ - ((typeof(*p) __force __kernel *)(local)); \ + ((typeof(*(p)) __force __kernel *)(local)); \ }) #define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
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