Messages in this thread | | | Date | Thu, 25 Aug 2022 14:32:43 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH 2/2] ARM: Replace this_cpu_* with raw_cpu_* in panic_bad_stack() |
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On Thu, Aug 25, 2022 at 02:31:54PM +0800, Zhen Lei wrote: > The hardware automatically disable the IRQ interrupt before jumping to the > interrupt or exception vector. Therefore, the preempt_disable() operation > in this_cpu_read() after macro expansion is unnecessary. In fact, function > this_cpu_read() may trigger scheduling, see pseudocode below. > > Pseudocode of this_cpu_read(xx): > preempt_disable_notrace(); > raw_cpu_read(xx); > if (unlikely(__preempt_count_dec_and_test())) > __preempt_schedule_notrace(); > > Therefore, use raw_cpu_* instead of this_cpu_* to eliminate potential > hazards. At the very least, it reduces a few lines of assembly code.
I think if scheduling is a problem here, something should increment the preempt_count as is done on arm64, since any other operation in this function could end up causing preemption.
Regardless, I also think it's sensible to use raw_cpu_*() here, but I don't think that actually fixes the problem the commit message describes.
Thanks, Mark.
> > Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> > --- > KernelVersion: v6.0-rc2 > arch/arm/kernel/traps.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c > index 1518a1f443ff866..d5903d790cf3b7e 100644 > --- a/arch/arm/kernel/traps.c > +++ b/arch/arm/kernel/traps.c > @@ -927,9 +927,9 @@ asmlinkage void handle_bad_stack(struct pt_regs *regs) > { > unsigned long tsk_stk = (unsigned long)current->stack; > #ifdef CONFIG_IRQSTACKS > - unsigned long irq_stk = (unsigned long)this_cpu_read(irq_stack_ptr); > + unsigned long irq_stk = (unsigned long)raw_cpu_read(irq_stack_ptr); > #endif > - unsigned long ovf_stk = (unsigned long)this_cpu_read(overflow_stack_ptr); > + unsigned long ovf_stk = (unsigned long)raw_cpu_read(overflow_stack_ptr); > > console_verbose(); > pr_emerg("Insufficient stack space to handle exception!"); > -- > 2.25.1 >
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