Re: [Crash-utility] [PATCH] Fix x86 initialization for {hard, soft}irq_ctx

----- Original Message ----- > > Current code is setting {hard,soft}irq_ctx[] to (irq_ctx **), because > per_cpu symbol itself is pointer of specified type (irq_ctx *). > > But, I wonder how this works in past, the code is expecting > {hard,soft}_ctx[] are (irq_ctx *). This fixes by deref per_cpu in > initialization, and set expected pointers. > > Tested on i386 v3.10. > You are correct -- apparently it never did work. The reason why I never noticed with RHEL kernels is that up until linux-2.6.29, the IRQ stacks were declared as a static NR_CPUS-bounded array: #ifdef CONFIG_4KSTACKS /* * per-CPU IRQ handling contexts (thread information and stack) */ union irq_ctx { struct thread_info tinfo; u32 stack[THREAD_SIZE/sizeof(u32)]; }; static union irq_ctx *hardirq_ctx[NR_CPUS] __read_mostly; static union irq_ctx *softirq_ctx[NR_CPUS] __read_mostly; static char softirq_stack[NR_CPUS * THREAD_SIZE] __page_aligned_bss; static char hardirq_stack[NR_CPUS * THREAD_SIZE] __page_aligned_bss; Then in linux-2.6.30, they were changed to be per-cpu variables: #ifdef CONFIG_4KSTACKS /* * per-CPU IRQ handling contexts (thread information and stack) */ union irq_ctx { struct thread_info tinfo; u32 stack[THREAD_SIZE/sizeof(u32)]; } __attribute__((aligned(PAGE_SIZE))); static DEFINE_PER_CPU(union irq_ctx *, hardirq_ctx); static DEFINE_PER_CPU(union irq_ctx *, softirq_ctx); static DEFINE_PER_CPU_PAGE_ALIGNED(union irq_ctx, hardirq_stack); static DEFINE_PER_CPU_PAGE_ALIGNED(union irq_ctx, softirq_stack); We never ran into the bug in 32-bit x86 RHEL6 (2.6.32-based) kernels because we did not configure CONFIG_4KSTACKS. Later on, the CONFIG_4KSTACKS restriction looks like it was removed, but we stopped supporting 32-bit x86 in RHEL7. And nobody ever reported it from any other x86 kernel sources. I also note that in linux-3.15 the data structure name and variables were changed to: struct irq_stack { u32 stack[THREAD_SIZE/sizeof(u32)]; } __aligned(THREAD_SIZE); DECLARE_PER_CPU(struct irq_stack *, hardirq_stack); DECLARE_PER_CPU(struct irq_stack *, softirq_stack); So your patch would need more work for 3.15 and later kernels. Thanks, Dave