[PATCH 2/3][mmotm] showing size of kcore v2

From: KAMEZAWA Hiroyuki
Date: Thu Sep 17 2009 - 02:12:30 EST


On Thu, 17 Sep 2009 14:02:39 +0800
AmÃrico Wang <xiyou.wangcong@xxxxxxxxx> wrote:
> > @@ -124,6 +126,7 @@ static void __kcore_update_ram(struct li
> > Â Â Â Âwrite_unlock(&kclist_lock);
> >
> > Â Â Â Âfree_kclist_ents(&garbage);
> > + Â Â Â proc_root_kcore->size = get_kcore_size(&nphdr, &size);
>
>
> This makes me to think if we will have some race condition here?
> Two processes can open kcore at the same time...
>
Finally,
==
static void __kcore_update_ram(struct list_head *list)
{
write_lock(&kclist_lock);
if (kcore_need_update) {
list_for_each_entry_safe(pos, tmp, &kclist_head, list) {
if (pos->type == KCORE_RAM
|| pos->type == KCORE_VMEMMAP)
list_move(&pos->list, &garbage);
}
list_splice_tail(list, &kclist_head);
} else
list_splice(list, &garbage);
kcore_need_update = 0;
write_unlock(&kclist_lock);
}

kclist itself is double checked under write_lock.
And, once updated, get_kcore_size()'s return vaule is static.
So, I think there are no race. But..Hmm...is this clearer ?

==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

Now, size of /proc/kcore which can be read by 'ls -l' is 0.
But it's not correct value.

This is a patch for showing size of /proc/kcore as following.

On x86-64, ls -l shows
... root root 140737486266368 2009-09-17 10:29 /proc/kcore
Then, 7FFFFFFE02000. This comes from vmalloc area's size.
This shows "core" size, not memory size.

This patch shows the size by updating "size" field in struct proc_dir_entry.
Later, lookup routine will create inode and fill inode->i_size based
on this value. Then, this has a problem.

- Once inode is cached, inode->i_size will never be updated.

Then, this patch is not memory-hotplug-aware.

To update inode->i_size, we have to know dentry or inode.
But there is no way to lookup them by inside kernel. Hmmm....
Next patch will try it.

Changelog:
-moved upadting ->size under lock.

Cc: WANG Cong <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
fs/proc/kcore.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

Index: mmotm-2.6.31-Sep14/fs/proc/kcore.c
===================================================================
--- mmotm-2.6.31-Sep14.orig/fs/proc/kcore.c
+++ mmotm-2.6.31-Sep14/fs/proc/kcore.c
@@ -107,6 +107,8 @@ static void free_kclist_ents(struct list
*/
static void __kcore_update_ram(struct list_head *list)
{
+ int nphdr;
+ size_t size;
struct kcore_list *tmp, *pos;
LIST_HEAD(garbage);

@@ -121,6 +123,7 @@ static void __kcore_update_ram(struct li
} else
list_splice(list, &garbage);
kcore_need_update = 0;
+ proc_root_kcore->size = get_kcore_size(&nphdr, &size);
write_unlock(&kclist_lock);

free_kclist_ents(&garbage);
@@ -429,7 +432,8 @@ read_kcore(struct file *file, char __use
unsigned long start;

read_lock(&kclist_lock);
- proc_root_kcore->size = size = get_kcore_size(&nphdr, &elf_buflen);
+ size = get_kcore_size(&nphdr, &elf_buflen);
+
if (buflen == 0 || *fpos >= size) {
read_unlock(&kclist_lock);
return 0;







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