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Subject[5/6] dynamically allocate IRQ stacks (was: Re: [-mm patch] i386: enable 4k stacks by default)
On Mon, Apr 30, 2007 at 10:38:19AM -0700, William Lee Irwin III wrote:
> Here's what I did for i386 for someone concerned about blowing the stack.

Fix up the conflict between IRQ stacks and deep stacks by dynamically
allocating IRQ stacks.

Signed-off-by: William Irwin <wli@holomorphy.com>


Index: stack-paranoia/arch/i386/Kconfig.debug
===================================================================
--- stack-paranoia.orig/arch/i386/Kconfig.debug 2007-04-30 10:34:07.058721717 -0700
+++ stack-paranoia/arch/i386/Kconfig.debug 2007-04-30 10:36:14.553987258 -0700
@@ -107,7 +107,6 @@

config 64KSTACKS
bool "Use 64KB for kernel stacks"
- depends on !IRQSTACKS
help
If you say Y here, the kernel will use a 64KB stacksize.
This impedes running more threads on a system and also increases
Index: stack-paranoia/arch/i386/kernel/irq.c
===================================================================
--- stack-paranoia.orig/arch/i386/kernel/irq.c 2007-04-30 10:34:07.058721717 -0700
+++ stack-paranoia/arch/i386/kernel/irq.c 2007-04-30 10:36:14.553987258 -0700
@@ -17,9 +17,11 @@
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/delay.h>
+#include <linux/bootmem.h>

#include <asm/apic.h>
#include <asm/uaccess.h>
+#include <asm/pgtable.h>

DEFINE_PER_CPU(irq_cpustat_t, irq_stat) ____cacheline_internodealigned_in_smp;
EXPORT_PER_CPU_SYMBOL(irq_stat);
@@ -56,8 +58,8 @@
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 DEFINE_PER_CPU(union irq_ctx *, hardirq_ctx);
+static DEFINE_PER_CPU(union irq_ctx *, softirq_ctx);
#endif

/*
@@ -102,7 +104,7 @@
#ifdef CONFIG_IRQSTACKS

curctx = (union irq_ctx *) current_thread_info();
- irqctx = hardirq_ctx[smp_processor_id()];
+ irqctx = per_cpu(hardirq_ctx, smp_processor_id());

/*
* this is where we switch to the IRQ stack. However, if we are
@@ -150,11 +152,44 @@
* These should really be __section__(".bss.page_aligned") as well, but
* gcc's 3.0 and earlier don't handle that correctly.
*/
-static char softirq_stack[NR_CPUS * THREAD_SIZE]
- __attribute__((__aligned__(THREAD_SIZE)));
+static DEFINE_PER_CPU(char *, softirq_stack);
+static DEFINE_PER_CPU(char *, hardirq_stack);

-static char hardirq_stack[NR_CPUS * THREAD_SIZE]
- __attribute__((__aligned__(THREAD_SIZE)));
+#ifdef CONFIG_VMALLOC_STACK
+static void * __init __alloc_irqstack(int cpu)
+{
+ int i;
+ struct page *pages[THREAD_SIZE/PAGE_SIZE], **tmp = pages;
+ struct vm_struct *area;
+
+ if (!cpu)
+ return __alloc_bootmem(THREAD_SIZE, THREAD_SIZE,
+ __pa(MAX_DMA_ADDRESS));
+
+ /* failures here are unrecoverable anyway */
+ area = get_vm_area(THREAD_SIZE, VM_IOREMAP);
+ for (i = 0; i < ARRAY_SIZE(pages); ++i)
+ pages[i] = alloc_page(GFP_HIGHUSER);
+ map_vm_area(area, PAGE_KERNEL, &tmp);
+ return area->addr;
+}
+#else /* !CONFIG_VMALLOC_STACK */
+static void * __init __alloc_irqstack(int cpu)
+{
+ if (!cpu)
+ return __alloc_bootmem(THREAD_SIZE, THREAD_SIZE,
+ __pa(MAX_DMA_ADDRESS));
+
+ return (void *)__get_free_pages(GFP_KERNEL,
+ ilog2(THREAD_SIZE/PAGE_SIZE));
+}
+#endif /* !CONFIG_VMALLOC_STACK */
+
+static void __init alloc_irqstacks(int cpu)
+{
+ per_cpu(softirq_stack, cpu) = __alloc_irqstack(cpu);
+ per_cpu(hardirq_stack, cpu) = __alloc_irqstack(cpu);
+}

/*
* allocate per-cpu stacks for hardirq and for softirq processing
@@ -163,34 +198,36 @@
{
union irq_ctx *irqctx;

- if (hardirq_ctx[cpu])
+ if (per_cpu(hardirq_ctx, cpu))
return;

- irqctx = (union irq_ctx*) &hardirq_stack[cpu*THREAD_SIZE];
+ alloc_irqstacks(cpu);
+
+ irqctx = (union irq_ctx*)per_cpu(hardirq_stack, cpu);
irqctx->tinfo.task = NULL;
irqctx->tinfo.exec_domain = NULL;
irqctx->tinfo.cpu = cpu;
irqctx->tinfo.preempt_count = HARDIRQ_OFFSET;
irqctx->tinfo.addr_limit = MAKE_MM_SEG(0);

- hardirq_ctx[cpu] = irqctx;
+ per_cpu(hardirq_ctx, cpu) = irqctx;

- irqctx = (union irq_ctx*) &softirq_stack[cpu*THREAD_SIZE];
+ irqctx = (union irq_ctx*)per_cpu(softirq_stack, cpu);
irqctx->tinfo.task = NULL;
irqctx->tinfo.exec_domain = NULL;
irqctx->tinfo.cpu = cpu;
irqctx->tinfo.preempt_count = 0;
irqctx->tinfo.addr_limit = MAKE_MM_SEG(0);

- softirq_ctx[cpu] = irqctx;
+ per_cpu(softirq_ctx, cpu) = irqctx;

printk("CPU %u irqstacks, hard=%p soft=%p\n",
- cpu,hardirq_ctx[cpu],softirq_ctx[cpu]);
+ cpu, per_cpu(hardirq_ctx, cpu), per_cpu(softirq_ctx, cpu));
}

void irq_ctx_exit(int cpu)
{
- hardirq_ctx[cpu] = NULL;
+ per_cpu(hardirq_ctx, cpu) = NULL;
}

extern asmlinkage void __do_softirq(void);
@@ -209,7 +246,7 @@

if (local_softirq_pending()) {
curctx = current_thread_info();
- irqctx = softirq_ctx[smp_processor_id()];
+ irqctx = per_cpu(softirq_ctx, smp_processor_id());
irqctx->tinfo.task = curctx->task;
irqctx->tinfo.previous_esp = current_stack_pointer;

-
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