linux-kernel - Re: [RFC 5/5] truncate: Remove unnecessary page release

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <AANLkTi=UfmZNfKWCisrs6ezzoWqpcwUOT5bs8LGwN7Rv@mail.gmail.com>
Date:	Mon, 20 Dec 2010 11:58:50 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC 5/5] truncate: Remove unnecessary page release

On Mon, Dec 20, 2010 at 11:27 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Mon, 20 Dec 2010 11:21:52 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
>
>> > This patch series changes remove_from_page_cache's page ref counting
>> > rule. page cache ref count is decreased in remove_from_page_cache.
>> > So we don't need call again in caller context.
>> >
>> > Cc: Nick Piggin <npiggin@...e.de>
>> > Cc: Al Viro <viro@...iv.linux.org.uk>
>> > Cc: linux-mm@...ck.org
>> > Signed-off-by: Minchan Kim <minchan.kim@...il.com>
>> > ---
>> >  mm/truncate.c |    1 -
>> >  1 files changed, 0 insertions(+), 1 deletions(-)
>> >
>> > diff --git a/mm/truncate.c b/mm/truncate.c
>> > index 9ee5673..8decb93 100644
>> > --- a/mm/truncate.c
>> > +++ b/mm/truncate.c
>> > @@ -114,7 +114,6 @@ truncate_complete_page(struct address_space *mapping, struct page *page)
>> >      * calls cleancache_put_page (and note page->mapping is now NULL)
>> >      */
>> >     cleancache_flush_page(mapping, page);
>> > -   page_cache_release(page);       /* pagecache ref */
>> >     return 0;
>>
>> Do we _always_ have stable page reference here? IOW, I can assume
>> cleancache_flush_page() doesn't cause NULL deref?
>>
> Hmm, my review was bad.
>
> I think cleancache_flush_page() here should eat (mapping, index) as argument
> rather than "page".
>
> BTW,  I can't understand
> ==
> void __cleancache_flush_page(struct address_space *mapping, struct page *page)
> {
>        /* careful... page->mapping is NULL sometimes when this is called */
>        int pool_id = mapping->host->i_sb->cleancache_poolid;
>        struct cleancache_filekey key = { .u.key = { 0 } };
> ==
>
> Why above is safe...
> I think (mapping,index) should be passed instead of page.

I don't think current code isn't safe.

void __cleancache_flush_page(struct address_space *mapping, struct page *page)
{
        /* careful... page->mapping is NULL sometimes when this is called */
        int pool_id = mapping->host->i_sb->cleancache_poolid;
        struct cleancache_filekey key = { .u.key = { 0 } };

        if (pool_id >= 0) {
                VM_BUG_ON(!PageLocked(page));

it does check PageLocked. So caller should hold a page reference to
prevent freeing ramined PG_locked
If the caller doesn't hold a ref of page, I think it's BUG of caller.

In our case, caller calls truncate_complete_page have to make sure it, I think.

>
>
> -Kame
>
>



-- 
Kind regards,
Minchan Kim
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/