Re: [Bug fix PATCH] resource: Reusing a resource structure allocatedby bootmem

[Yasuaki Ishimatsu]

Hi Toshi,

2013/04/16 5:01, Toshi Kani wrote:
> On Mon, 2013-04-15 at 11:15 +0900, Yasuaki Ishimatsu wrote:
> > When hot removing memory presented at boot time, following messages are shown:
>
> :
>
> > The reason why the messages are shown is to release a resource structure,
> > allocated by bootmem, by kfree(). So when we release a resource structure,
> > we should check whether it is allocated by bootmem or not.
> >
> > But even if we know a resource structure is allocated by bootmem, we cannot
> > release it since SLxB cannot treat it. So for reusing a resource structure,
> > this patch remembers it by using bootmem_resource as follows:
> >
> > When releasing a resource structure by free_resource(), free_resource() checks
> > whether the resource structure is allocated by bootmem or not. If it is
> > allocated by bootmem, free_resource() adds it to bootmem_resource. If it is
> > not allocated by bootmem, free_resource() release it by kfree().
> >
> > And when getting a new resource structure by get_resource(), get_resource()
> > checks whether bootmem_resource has released resource structures or not. If
> > there is a released resource structure, get_resource() returns it. If there is
> > not a releaed resource structure, get_resource() returns new resource structure
> > allocated by kzalloc().
>
> Thanks for fixing this existing issue that also needed to be addressed.
> I am not able to test this particular case in my test env, so I did not
> notice it.

> Can you update this patch to base off of the patch below?  Otherwise, it
> won't apply cleanly.
> https://lkml.org/lkml/2013/4/11/694

O.K. I'll update it.

> More comments below.
>
> > Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
> > ---
> > This patch is baseg on following Toshi's works:
> > Support memory hot-delete to boot memory
> >    https://lkml.org/lkml/2013/4/10/469
> >
> >   kernel/resource.c |   72 +++++++++++++++++++++++++++++++++++++++++++---------
> >   1 files changed, 59 insertions(+), 13 deletions(-)
> >
> > diff --git a/kernel/resource.c b/kernel/resource.c
> > index 16bfd39..152e9aa 100644
> > --- a/kernel/resource.c
> > +++ b/kernel/resource.c
> > @@ -21,6 +21,7 @@
> >   #include <linux/seq_file.h>
> >   #include <linux/device.h>
> >   #include <linux/pfn.h>
> > +#include <linux/mm.h>
> >   #include <asm/io.h>
> >
> >
> > @@ -50,6 +51,16 @@ struct resource_constraint {
> >
> >   static DEFINE_RWLOCK(resource_lock);
> >
> > +/*
> > + * For memory hotplug, there is no way to free resource entries allocated
> > + * by boot mem after the system is up. So for reusing the resource entry
> > + * we need to remember the resource.
> > + */
> > +struct resource bootmem_resource = {
> > +	.sibling = NULL,
> > +};
> > +static DEFINE_SPINLOCK(bootmem_resource_lock);
> > +
> >   static void *r_next(struct seq_file *m, void *v, loff_t *pos)
> >   {
> >   	struct resource *p = v;
> > @@ -151,6 +162,42 @@ __initcall(ioresources_init);
> >
> >   #endif /* CONFIG_PROC_FS */
> >
> > +static void __free_resource(struct resource *res)
> > +{
> > +	struct resource *next_res = bootmem_resource.sibling;
> > +
> > +	bootmem_resource.sibling = res;
> > +	res->sibling = next_res;
> > +}
> > +
> > +static void free_resource(struct resource *res)
> > +{

> You need to add the following if-statement here.  Otherwise it hits a
> page fault when res is NULL.  This case happens when a resource entry
> splits into two entries.
>
> 	if (!res)
> 		return;

I'll update it.

> > +	if (PageReserved(virt_to_page(res))) {
> > +		spin_lock(&bootmem_resource_lock);
> > +		__free_resource(res);

> How about simply updating the link here, instead of having it done in
> __free_resource()?  I think it makes it more consistent with
> get_resource().
>
> 		res->sibling = bootmem_resource.sibling;
> 		bootmem_resource.sibling = res;

I'll update it.

Thanks,
Yasuaki Ishimatsu

> Thanks,
> -Toshi
>
> > +		spin_unlock(&bootmem_resource_lock);
> > +	} else {
> > +		kfree(res);
> > +	}
> > +}


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