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

From: Yasuaki Ishimatsu
Date: Mon Apr 15 2013 - 20:35:39 EST


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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