On Fri, Sep 17, 2021 at 10:23:48AM +0200, Peter Zijlstra wrote: > On Fri, Sep 17, 2021 at 11:58:59AM +1000, Stephen Rothwell wrote: > > Hi all, > > > > After merging the tip tree, today's linux-next build (x86_64 allmodconfig) > > produced this warning: > > > > vmlinux.o: warning: objtool: mce_setup()+0x22: call to memset() leaves .noinstr.text section > > vmlinux.o: warning: objtool: do_machine_check()+0x51: call to mce_gather_info() leaves .noinstr.text section > > Those are pre-existing and Boris is lokoing into them, these however, > are new: > > > vmlinux.o: warning: objtool: rcu_dynticks_eqs_enter()+0x0: call to rcu_dynticks_task_trace_enter() leaves .noinstr.text section > > vmlinux.o: warning: objtool: rcu_dynticks_eqs_exit()+0xe: call to rcu_dynticks_task_trace_exit() leaves .noinstr.text section > > These are from 7d0c9c50c5a1 ("rcu-tasks: Avoid IPIing userspace/idle > tasks if kernel is so built"). > > The below seems to help. > > > vmlinux.o: warning: objtool: rcu_nmi_enter()+0x36: call to __kasan_check_read() leaves .noinstr.text section > > That's 2be57f732889 ("rcu: Weaken ->dynticks accesses and updates"), > doing: > > - return !(arch_atomic_read(&this_cpu_ptr(&rcu_data)->dynticks) & 0x1); > + return !(atomic_read(this_cpu_ptr(&rcu_data.dynticks)) & 0x1); > > and causing instrumentation to be inserted where none is acceptable. > Flipping that back to arch_atomic_read() makes it go away as expected. The 2be57f732889 commit went in during the v5.15 merge window and the 7d0c9c50c5a1 went into v5.8, but perhaps Linus won't be averse to taking a fix for an older bug along with the regression. ;-) Given no Signed-off-by, I am guessing that you would like to push this separately. If so: Tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > --- > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index 1a6fdb03d0a5..5199559fbbf0 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -1479,7 +1479,7 @@ static void rcu_bind_gp_kthread(void) > } > > /* Record the current task on dyntick-idle entry. */ > -static void noinstr rcu_dynticks_task_enter(void) > +static __always_inline void rcu_dynticks_task_enter(void) > { > #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) > WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id()); > @@ -1487,7 +1487,7 @@ static void noinstr rcu_dynticks_task_enter(void) > } > > /* Record no current task on dyntick-idle exit. */ > -static void noinstr rcu_dynticks_task_exit(void) > +static __always_inline void rcu_dynticks_task_exit(void) > { > #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) > WRITE_ONCE(current->rcu_tasks_idle_cpu, -1); > @@ -1495,7 +1495,7 @@ static void noinstr rcu_dynticks_task_exit(void) > } > > /* Turn on heavyweight RCU tasks trace readers on idle/user entry. */ > -static void rcu_dynticks_task_trace_enter(void) > +static __always_inline void rcu_dynticks_task_trace_enter(void) > { > #ifdef CONFIG_TASKS_TRACE_RCU > if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) > @@ -1504,7 +1504,7 @@ static void rcu_dynticks_task_trace_enter(void) > } > > /* Turn off heavyweight RCU tasks trace readers on idle/user exit. */ > -static void rcu_dynticks_task_trace_exit(void) > +static __always_inline void rcu_dynticks_task_trace_exit(void) > { > #ifdef CONFIG_TASKS_TRACE_RCU > if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) >