Re: [PATCH V1] x86, espfix: postpone the initialization of espfix stack for AP

[Zhu Guihua <zhugh.fnst@cn.fujitsu.com>]

Any feedback about this?

On 06/04/2015 05:45 PM, Gu Zheng wrote:
> The following lockdep warning occurrs when running with latest kernel:
> [    3.178000] ------------[ cut here ]------------
> [    3.183000] WARNING: CPU: 128 PID: 0 at kernel/locking/lockdep.c:2755 lockdep_trace_alloc+0xdd/0xe0()
> [    3.193000] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
> [    3.199000] Modules linked in:
>
> [    3.203000] CPU: 128 PID: 0 Comm: swapper/128 Not tainted 4.1.0-rc3 #70
> [    3.221000]  0000000000000000 2d6601fb3e6d4e4c ffff88086fd5fc38 ffffffff81773f0a
> [    3.230000]  0000000000000000 ffff88086fd5fc90 ffff88086fd5fc78 ffffffff8108c85a
> [    3.238000]  ffff88086fd60000 0000000000000092 ffff88086fd60000 00000000000000d0
> [    3.246000] Call Trace:
> [    3.249000]  [<ffffffff81773f0a>] dump_stack+0x4c/0x65
> [    3.255000]  [<ffffffff8108c85a>] warn_slowpath_common+0x8a/0xc0
> [    3.261000]  [<ffffffff8108c8e5>] warn_slowpath_fmt+0x55/0x70
> [    3.268000]  [<ffffffff810ee24d>] lockdep_trace_alloc+0xdd/0xe0
> [    3.274000]  [<ffffffff811cda0d>] __alloc_pages_nodemask+0xad/0xca0
> [    3.281000]  [<ffffffff810ec7ad>] ? __lock_acquire+0xf6d/0x1560
> [    3.288000]  [<ffffffff81219c8a>] alloc_page_interleave+0x3a/0x90
> [    3.295000]  [<ffffffff8121b32d>] alloc_pages_current+0x17d/0x1a0
> [    3.301000]  [<ffffffff811c869e>] ? __get_free_pages+0xe/0x50
> [    3.308000]  [<ffffffff811c869e>] __get_free_pages+0xe/0x50
> [    3.314000]  [<ffffffff8102640b>] init_espfix_ap+0x17b/0x320
> [    3.320000]  [<ffffffff8105c691>] start_secondary+0xf1/0x1f0
> [    3.327000] ---[ end trace 1b3327d9d6a1d62c ]---
>
> As we alloc pages with GFP_KERNEL in init_espfix_ap() which is called
> before enabled local irq, and the lockdep sub-system considers this
> behaviour as allocating memory with GFP_FS with local irq disabled,
> then trigger the warning as mentioned about.
>
> Though we could allocate them on the boot CPU side and hand them over to
> the secondary CPU, but it seemes a bit waste if some of cpus are offline.
> As thers is no need to these pages(espfix stack) until we try to run user
> code, so we postpone the initialization of espfix stack, and let the boot
> up routine init the espfix stack for the target cpu after it booted to
> avoid the noise.
>
> Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
> ---
> v1:
>    Alloc the page on the node the target CPU is on.
> RFC:
>    Let the boot up routine init the espfix stack for the target cpu after it
>    booted.
> ---
> ---
>   arch/x86/include/asm/espfix.h |    2 +-
>   arch/x86/kernel/espfix_64.c   |   28 ++++++++++++++++------------
>   arch/x86/kernel/smpboot.c     |   14 +++++++-------
>   3 files changed, 24 insertions(+), 20 deletions(-)
>
> diff --git a/arch/x86/include/asm/espfix.h b/arch/x86/include/asm/espfix.h
> index 99efebb..ca3ce9a 100644
> --- a/arch/x86/include/asm/espfix.h
> +++ b/arch/x86/include/asm/espfix.h
> @@ -9,7 +9,7 @@ DECLARE_PER_CPU_READ_MOSTLY(unsigned long, espfix_stack);
>   DECLARE_PER_CPU_READ_MOSTLY(unsigned long, espfix_waddr);
>   
>   extern void init_espfix_bsp(void);
> -extern void init_espfix_ap(void);
> +extern void init_espfix_ap(int cpu);
>   
>   #endif /* CONFIG_X86_64 */
>   
> diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
> index f5d0730..e397583 100644
> --- a/arch/x86/kernel/espfix_64.c
> +++ b/arch/x86/kernel/espfix_64.c
> @@ -131,25 +131,24 @@ void __init init_espfix_bsp(void)
>   	init_espfix_random();
>   
>   	/* The rest is the same as for any other processor */
> -	init_espfix_ap();
> +	init_espfix_ap(0);
>   }
>   
> -void init_espfix_ap(void)
> +void init_espfix_ap(int cpu)
>   {
> -	unsigned int cpu, page;
> +	unsigned int page;
>   	unsigned long addr;
>   	pud_t pud, *pud_p;
>   	pmd_t pmd, *pmd_p;
>   	pte_t pte, *pte_p;
> -	int n;
> +	int n, node;
>   	void *stack_page;
>   	pteval_t ptemask;
>   
>   	/* We only have to do this once... */
> -	if (likely(this_cpu_read(espfix_stack)))
> +	if (likely(per_cpu(espfix_stack, cpu)))
>   		return;		/* Already initialized */
>   
> -	cpu = smp_processor_id();
>   	addr = espfix_base_addr(cpu);
>   	page = cpu/ESPFIX_STACKS_PER_PAGE;
>   
> @@ -165,12 +164,15 @@ void init_espfix_ap(void)
>   	if (stack_page)
>   		goto unlock_done;
>   
> +	node = cpu_to_node(cpu);
>   	ptemask = __supported_pte_mask;
>   
>   	pud_p = &espfix_pud_page[pud_index(addr)];
>   	pud = *pud_p;
>   	if (!pud_present(pud)) {
> -		pmd_p = (pmd_t *)__get_free_page(PGALLOC_GFP);
> +		struct page *page = alloc_pages_node(node, PGALLOC_GFP, 0);
> +
> +		pmd_p = (pmd_t *)page_address(page);
>   		pud = __pud(__pa(pmd_p) | (PGTABLE_PROT & ptemask));
>   		paravirt_alloc_pmd(&init_mm, __pa(pmd_p) >> PAGE_SHIFT);
>   		for (n = 0; n < ESPFIX_PUD_CLONES; n++)
> @@ -180,7 +182,9 @@ void init_espfix_ap(void)
>   	pmd_p = pmd_offset(&pud, addr);
>   	pmd = *pmd_p;
>   	if (!pmd_present(pmd)) {
> -		pte_p = (pte_t *)__get_free_page(PGALLOC_GFP);
> +		struct page *page = alloc_pages_node(node, PGALLOC_GFP, 0);
> +
> +		pte_p = (pte_t *)page_address(page);
>   		pmd = __pmd(__pa(pte_p) | (PGTABLE_PROT & ptemask));
>   		paravirt_alloc_pte(&init_mm, __pa(pte_p) >> PAGE_SHIFT);
>   		for (n = 0; n < ESPFIX_PMD_CLONES; n++)
> @@ -188,7 +192,7 @@ void init_espfix_ap(void)
>   	}
>   
>   	pte_p = pte_offset_kernel(&pmd, addr);
> -	stack_page = (void *)__get_free_page(GFP_KERNEL);
> +	stack_page = page_address(alloc_pages_node(node, GFP_KERNEL, 0));
>   	pte = __pte(__pa(stack_page) | (__PAGE_KERNEL_RO & ptemask));
>   	for (n = 0; n < ESPFIX_PTE_CLONES; n++)
>   		set_pte(&pte_p[n*PTE_STRIDE], pte);
> @@ -199,7 +203,7 @@ void init_espfix_ap(void)
>   unlock_done:
>   	mutex_unlock(&espfix_init_mutex);
>   done:
> -	this_cpu_write(espfix_stack, addr);
> -	this_cpu_write(espfix_waddr, (unsigned long)stack_page
> -		       + (addr & ~PAGE_MASK));
> +	per_cpu(espfix_stack, cpu) = addr;
> +	per_cpu(espfix_waddr, cpu) = (unsigned long)stack_page
> +		       + (addr & ~PAGE_MASK);
>   }
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 50e547e..e9fdd0e 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -240,13 +240,6 @@ static void notrace start_secondary(void *unused)
>   	check_tsc_sync_target();
>   
>   	/*
> -	 * Enable the espfix hack for this CPU
> -	 */
> -#ifdef CONFIG_X86_ESPFIX64
> -	init_espfix_ap();
> -#endif
> -
> -	/*
>   	 * We need to hold vector_lock so there the set of online cpus
>   	 * does not change while we are assigning vectors to cpus.  Holding
>   	 * this lock ensures we don't half assign or remove an irq from a cpu.
> @@ -901,6 +894,13 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
>   		}
>   	}
>   
> +	/*
> +	 * Enable the espfix hack for this CPU
> +	 */
> +#ifdef CONFIG_X86_ESPFIX64
> +	init_espfix_ap(cpu);
> +#endif
> +
>   	/* mark "stuck" area as not stuck */
>   	*trampoline_status = 0;
>