* Re: [trival patch]disable warning in cpu_init for cpu hotplug
2006-03-23 5:32 ` Andrew Morton
@ 2006-03-23 6:19 ` Shaohua Li
0 siblings, 0 replies; 3+ messages in thread
From: Shaohua Li @ 2006-03-23 6:19 UTC (permalink / raw)
To: Andrew Morton; +Cc: linux-kernel
On Wed, 2006-03-22 at 21:32 -0800, Andrew Morton wrote:
> Shaohua Li <shaohua.li@intel.com> wrote:
> >
> > The patch seems missed.
> > GFP_KERNEL isn't ok for runtime (cpu hotplug).
> >
> > Signed-off-by: Shaohua Li<shaohua.li@intel.com>
> > ---
> >
> > linux-2.6.15-root/arch/i386/kernel/cpu/common.c | 2 +-
> > 1 files changed, 1 insertion(+), 1 deletion(-)
> >
> > diff -puN arch/i386/kernel/cpu/common.c~cpuhp arch/i386/kernel/cpu/common.c
> > --- linux-2.6.15/arch/i386/kernel/cpu/common.c~cpuhp 2006-03-14 12:13:43.000000000 +0800
> > +++ linux-2.6.15-root/arch/i386/kernel/cpu/common.c 2006-03-14 12:14:12.000000000 +0800
> > @@ -605,7 +605,7 @@ void __devinit cpu_init(void)
> > /* alloc_bootmem_pages panics on failure, so no check */
> > memset(gdt, 0, PAGE_SIZE);
> > } else {
> > - gdt = (struct desc_struct *)get_zeroed_page(GFP_KERNEL);
> > + gdt = (struct desc_struct *)get_zeroed_page(GFP_ATOMIC);
> > if (unlikely(!gdt)) {
> > printk(KERN_CRIT "CPU%d failed to allocate GDT\n", cpu);
> > for (;;)
>
>
> This isn't good. GFP_ATOMIC can fail, and if it does, we'll lose this CPU
> and probably the entire machine. It's OK to do this during initial boot,
> but not so OK to do it during CPU hotplug.
>
> So can we please fix it better?
>
> You don't describe _why_ the CPU is running atomically here - I wish you had.
>
> One approach would be to allocate the page earlier, before we enter the
> atomic region, and to pass that page down to cpu_init(), or to save a
> pointer to it in an array of page*'s somewhere.
Thanks for the suggestion. Here is the updated patch.
The patch fixes two issues:
1. cpu_init is called with interrupt disabled. Allocating gdt table
there isn't good at runtime.
2. gdt table page cause memory leak in CPU hotplug case.
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
---
linux-2.6.16-root/arch/i386/kernel/cpu/common.c | 8 +++++++-
linux-2.6.16-root/arch/i386/kernel/smpboot.c | 13 +++++++++++++
2 files changed, 20 insertions(+), 1 deletion(-)
diff -puN arch/i386/kernel/cpu/common.c~gdt_table arch/i386/kernel/cpu/common.c
--- linux-2.6.16/arch/i386/kernel/cpu/common.c~gdt_table 2006-03-22 11:57:56.000000000 +0800
+++ linux-2.6.16-root/arch/i386/kernel/cpu/common.c 2006-03-22 12:10:04.000000000 +0800
@@ -594,6 +594,12 @@ void __devinit cpu_init(void)
set_in_cr4(X86_CR4_TSD);
}
+ /* The CPU hotplug case */
+ if (cpu_gdt_descr->address) {
+ gdt = (struct desc_struct *)cpu_gdt_descr->address;
+ memset(gdt, 0, PAGE_SIZE);
+ goto old_gdt;
+ }
/*
* This is a horrible hack to allocate the GDT. The problem
* is that cpu_init() is called really early for the boot CPU
@@ -612,7 +618,7 @@ void __devinit cpu_init(void)
local_irq_enable();
}
}
-
+old_gdt:
/*
* Initialize the per-CPU GDT with the boot GDT,
* and set up the GDT descriptor:
diff -puN arch/i386/kernel/smpboot.c~gdt_table arch/i386/kernel/smpboot.c
--- linux-2.6.16/arch/i386/kernel/smpboot.c~gdt_table 2006-03-22 12:01:41.000000000 +0800
+++ linux-2.6.16-root/arch/i386/kernel/smpboot.c 2006-03-22 12:18:28.000000000 +0800
@@ -1027,6 +1027,7 @@ int __devinit smp_prepare_cpu(int cpu)
struct warm_boot_cpu_info info;
struct work_struct task;
int apicid, ret;
+ struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
lock_cpu_hotplug();
@@ -1045,6 +1046,18 @@ int __devinit smp_prepare_cpu(int cpu)
goto exit;
}
+ /*
+ * the CPU isn't initialized at boot time, allocate gdt table here.
+ * cpu_init will initialize it
+ */
+ if (!cpu_gdt_descr->address) {
+ cpu_gdt_descr->address = get_zeroed_page(GFP_KERNEL);
+ if (!cpu_gdt_descr->address)
+ printk(KERN_CRIT "CPU%d failed to allocate GDT\n", cpu);
+ ret = -ENOMEM;
+ goto exit;
+ }
+
info.complete = &done;
info.apicid = apicid;
info.cpu = cpu;
_
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