On Thu, 4 Nov 2021 at 09:31, Helge Deller <deller@xxxxxx> wrote:
>
> On 11/4/21 09:26, Ard Biesheuvel wrote:
> > In commit 2214c0e77259 ("parisc: Move thread_info into task struct")
> > PA-RISC gained support for THREAD_INFO_IN_TASK while changes were
> > already underway to keep the CPU field in thread_info rather than move
> > it into task_struct when THREAD_INFO_IN_TASK is enabled. The result is a
> > broken build for all PA-RISC configs that enable SMP.
> >
> > So let's partially revert that commit, and get rid of the ugly hack to
> > get at the offset of task_struct::cpu without having to include
> > linux/sched.h, and put the CPU field back where it was before.
> >
> > Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > Fixes: bcf9033e5449 ("sched: move CPU field back into thread_info if THREAD_INFO_IN_TASK=y")
> > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
>
> Thanks Ard!
>
> I actually had the same patch finished right now too :-)
>
I was wondering about that :-)
> One small nid though. See below...
>
>
> > ---
> > arch/parisc/include/asm/smp.h | 19 ++-----------------
> > arch/parisc/include/asm/thread_info.h | 2 ++
> > arch/parisc/kernel/asm-offsets.c | 4 +---
> > arch/parisc/kernel/smp.c | 2 +-
> > 4 files changed, 6 insertions(+), 21 deletions(-)
> >
> > diff --git a/arch/parisc/include/asm/smp.h b/arch/parisc/include/asm/smp.h
> > index 16d41127500e..cba55abf7bac 100644
> > --- a/arch/parisc/include/asm/smp.h
> > +++ b/arch/parisc/include/asm/smp.h
> > @@ -34,23 +34,8 @@ extern void arch_send_call_function_ipi_mask(const struct cpumask *mask);
> >
> > #endif /* !ASSEMBLY */
> >
> > -/*
> > - * This is particularly ugly: it appears we can't actually get the definition
> > - * of task_struct here, but we need access to the CPU this task is running on.
> > - * Instead of using task_struct we're using TASK_CPU which is extracted from
> > - * asm-offsets.h by kbuild to get the current processor ID.
> > - *
> > - * This also needs to be safeguarded when building asm-offsets.s because at
> > - * that time TASK_CPU is not defined yet. It could have been guarded by
> > - * TASK_CPU itself, but we want the build to fail if TASK_CPU is missing
> > - * when building something else than asm-offsets.s
> > - */
> > -#ifdef GENERATING_ASM_OFFSETS
> > -#define raw_smp_processor_id() (0)
> > -#else
> > -#include <asm/asm-offsets.h>
> > -#define raw_smp_processor_id() (*(unsigned int *)((void *)current + TASK_CPU))
> > -#endif
> > +#define raw_smp_processor_id() (current_thread_info()->cpu)
> > +
> > #else /* CONFIG_SMP */
> >
> > static inline void smp_send_all_nop(void) { return; }
> > diff --git a/arch/parisc/include/asm/thread_info.h b/arch/parisc/include/asm/thread_info.h
> > index 75657c2c54e1..d6268834bfa5 100644
> > --- a/arch/parisc/include/asm/thread_info.h
> > +++ b/arch/parisc/include/asm/thread_info.h
> > @@ -8,12 +8,14 @@
> >
> > struct thread_info {
> > unsigned long flags; /* thread_info flags (see TIF_*) */
> > + __u32 cpu; /* current CPU */
> > int preempt_count; /* 0=premptable, <0=BUG; will also serve as bh-counter */
> > };
> >
> > #define INIT_THREAD_INFO(tsk) \
> > { \
> > .flags = 0, \
> > + .cpu = 0, \
> > .preempt_count = INIT_PREEMPT_COUNT, \
> > }
> >
> > diff --git a/arch/parisc/kernel/asm-offsets.c b/arch/parisc/kernel/asm-offsets.c
> > index e35154035441..629d38e36e22 100644
> > --- a/arch/parisc/kernel/asm-offsets.c
> > +++ b/arch/parisc/kernel/asm-offsets.c
> > @@ -14,8 +14,6 @@
> > * Copyright (C) 2003 James Bottomley <jejb at parisc-linux.org>
> > */
> >
> > -#define GENERATING_ASM_OFFSETS /* asm/smp.h */
> > -
> > #include <linux/types.h>
> > #include <linux/sched.h>
> > #include <linux/thread_info.h>
> > @@ -40,7 +38,7 @@ int main(void)
> > DEFINE(TASK_TI_FLAGS, offsetof(struct task_struct, thread_info.flags));
> > DEFINE(TASK_STACK, offsetof(struct task_struct, stack));
> > #ifdef CONFIG_SMP
> > - DEFINE(TASK_CPU, offsetof(struct task_struct, cpu));
> > + DEFINE(TASK_CPU, offsetof(struct task_struct, thread_info.cpu));
> > #endif
>
> The TASK_CPU define isn't needed any longer.
> So, the whole part inside #ifdef..#endif can go.
>
OK let's just drop it then.
> > BLANK();
> > DEFINE(TASK_REGS, offsetof(struct task_struct, thread.regs));
> > diff --git a/arch/parisc/kernel/smp.c b/arch/parisc/kernel/smp.c
> > index 171925285f3e..0cd97fa004c5 100644
> > --- a/arch/parisc/kernel/smp.c
> > +++ b/arch/parisc/kernel/smp.c
> > @@ -339,7 +339,7 @@ int smp_boot_one_cpu(int cpuid, struct task_struct *idle)
> > const struct cpuinfo_parisc *p = &per_cpu(cpu_data, cpuid);
> > long timeout;
> >
> > - idle->cpu = cpuid;
> > + task_thread_info(idle)->cpu = cpuid;
I was wondering if this could simply be dropped altogether? I am
pretty sure it is redundant, as the core code sets this field as well,
but I don't have access to a SMP PA-RISC machine to test it.
> >
> > /* Let _start know what logical CPU we're booting
> > ** (offset into init_tasks[],cpu_data[])
> >
> If it's Ok for you I'll clean up your patch and submit
> all with the next pull request to Linus later today.
>
Whatever works for you is fine with me.
