hi On Fri, Mar 18, 2022 at 4:20 AM Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > On Thu, Mar 17, 2022 at 04:45:11PM +0000, Hyeonggon Yoo wrote: > > On Thu, Mar 17, 2022 at 09:20:33AM -0700, Paul E. McKenney wrote: > > > On Thu, Mar 17, 2022 at 03:24:42PM +0000, Hyeonggon Yoo wrote: > > > > On Thu, Mar 17, 2022 at 07:00:00AM -0700, Paul E. McKenney wrote: > > > > > On Thu, Mar 17, 2022 at 11:32:53AM +0000, Hyeonggon Yoo wrote: > > > > > > Hello RCU folks, > > > > > > > > > > > > I like to use minimal configuration for kernel development. > > > > > > when building with tinyconfig + CONFIG_PREEMPT=y on arm64: > > > > > > > > > > > > ld: kernel/rcu/update.o: in function `call_rcu_tasks': > > > > > > update.c:(.text+0xb2c): undefined reference to `irq_work_queue' > > > > > > update.c:(.text+0xb2c): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `irq_work_queue' > > > > > > make: *** [Makefile:1155: vmlinux] Error 1 > > > > > > > > > > > > It seems RCU calls irq_work_queue() without checking if CONFIG_IRQ_WORK is enabled. > > > > > > > > > > Indeed it does! > > > > > > > > > > And kernel/rcu/Kconfig shows why: > > > > > > > > > > config TASKS_TRACE_RCU > > > > > def_bool 0 > > > > > select IRQ_WORK > > > > > help > > > > > This option enables a task-based RCU implementation that uses > > > > > explicit rcu_read_lock_trace() read-side markers, and allows > > > > > these readers to appear in the idle loop as well as on the CPU > > > > > hotplug code paths. It can force IPIs on online CPUs, including > > > > > idle ones, so use with caution. > > > > > > > > > > So the solution is to further minimize your configuration so as to > > > > > deselect TASKS_TRACE_RCU. > > > > > > > > They are already not selected. > > > > > > Good, thank you. > > > > > > How about TASKS_RUDE_RCU, TASKS_TRACE_RCU, and TASKS_RCU_GENERIC? > > > > TASKS_RUDE_RCU=n > > TASKS_TRACE_RCU=n > > TASKS_RCU_GENERIC=y > > TASKS_RCU=y > > > > > > > This means making sure that both BPF and > > > > > the various RCU torture tests are all deselected. > > > > > > > > I wanted to say call_rcu_tasks() can be referenced even when IRQ_WORK is not > > > > selected, making it fail to build. > > > > > > I am guessing because TASKS_RCU_GENERIC is selected? > > > > > > > Right. > > > > > If so, does the patch at the end of this email help? > > > > > > > No. did not help. > > > > I think I found reason... > > with PREEMPTION=y, > > > > in kernel/rcu/Kconfig: > > config TASKS_RCU > > def_bool PREEMPTION > > help > > This option enables a task-based RCU implementation that uses > > only voluntary context switch (not preemption!), idle, and > > user-mode execution as quiescent states. Not for manual selection. > > > > in kernel/rcu/Kconfig: > > config TASKS_RCU_GENERIC > > def_bool TASKS_RCU || TASKS_RUDE_RCU || TASKS_TRACE_RCU > > select SRCU > > help > > This option enables generic infrastructure code supporting > > task-based RCU implementations. Not for manual selection. > > Ah, this is because some of the tracing code uses TASKS_RCU only > when PREEMPTION=y. That would be KPROBES and TRACING. Maybe also > TRACE_CLOCK and TRACEPOINTS, but I would hope that TRACING would > cover those. Adding the tracing guys for their thoughts. > > > > > > > ld: kernel/rcu/update.o: in function `call_rcu_tasks': > > > > > > update.c:(.text+0xb2c): undefined reference to `irq_work_queue' > > > > > > update.c:(.text+0xb2c): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `irq_work_queue' > > > > > > make: *** [Makefile:1155: vmlinux] Error 1 > > > > > > > > Isn't it better to fix this build failure? > > > > > > But of course! However, first I need to know exactly what is causing your > > > build failure. I cannot see your .config file, so I am having to guess. > > > > > > Don't get me wrong, I do have a lot of practice guessing, but it is still > > > just guessing. ;-) > > > > Sorry to make you guess. Maybe too late, but added config as attachment ;) > > Perhaps I needed the practice. ;-) > > > > > It fails to build when both TASKS_TRACE_RCU and IRQ_WORK are not selected > > > > and PREEMPT is selected. > > > > > > > > │ Symbol: TASKS_TRACE_RCU [=n] │ > > > > │ Type : bool │ > > > > │ Defined at kernel/rcu/Kconfig:96 │ > > > > │ Selects: IRQ_WORK [=n] │ > > > > │ Selected by [n]: │ > > > > │ - BPF_SYSCALL [=n] │ > > > > │ - RCU_SCALE_TEST [=n] && DEBUG_KERNEL [=y] │ > > > > │ - RCU_TORTURE_TEST [=n] && DEBUG_KERNEL [=y] │ > > > > │ - RCU_REF_SCALE_TEST [=n] && DEBUG_KERNEL [=y] > > > > > > > > Thanks! > > > > > > > > > > > > > > Or turn on IRQ_WORK, for example, if you need to use BPF. > > > > > > Or do you already have TASKS_RCU_GENERIC deselected? > > > > > > > No, this is selected. TASKS_RCU_GENERIC=y. because of PREEMPTION=y. > > OK, the patch shown below allows me to get TASKS_RCU_GENERIC=n even > with PREEMPTION=y. This might somehow subtly break tracing, but in > that case further adjustments can be made. Untested other than > generating a few .config combinations. > > Thoughts? > > Thanx, Paul > > ------------------------------------------------------------------------ > > diff --git a/arch/Kconfig b/arch/Kconfig > index 678a80713b21..66c5b5543511 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -38,6 +38,7 @@ config KPROBES > depends on MODULES > depends on HAVE_KPROBES > select KALLSYMS > + select TASKS_RCU if PREEMPTION > help > Kprobes allows you to trap at almost any kernel address and > execute a callback function. register_kprobe() establishes > diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig > index f559870fbf8b..4f665ae0cf55 100644 > --- a/kernel/rcu/Kconfig > +++ b/kernel/rcu/Kconfig > @@ -78,7 +78,8 @@ config TASKS_RCU_GENERIC > task-based RCU implementations. Not for manual selection. > > config TASKS_RCU > - def_bool PREEMPTION > + def_bool 0 > + select IRQ_WORK > help > This option enables a task-based RCU implementation that uses > only voluntary context switch (not preemption!), idle, and > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig > index 752ed89a293b..a7aaf150b704 100644 > --- a/kernel/trace/Kconfig > +++ b/kernel/trace/Kconfig > @@ -127,6 +127,7 @@ config TRACING > select BINARY_PRINTF > select EVENT_TRACING > select TRACE_CLOCK > + select TASKS_RCU if PREEMPTION > > config GENERIC_TRACER > bool I apply above patch, and invoke $make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- CC=aarch64-linux-gnu-gcc-10 tinyconfig $make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- CC=aarch64-linux-gnu-gcc-10 -j 16 kernel build successful this time (without above patch, kernel build will quit with undefined reference to `irq_work_queue' Tested-by: Zhouyi Zhou<zhouzhouyi@xxxxxxxxx> Thanks Zhouyi
