linux-kernel - Re: [patch 1/2] mm: dont clear PG_uptodate in invalidate_complete

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]

Date:	Wed, 25 Jun 2008 20:18:02 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	jens.axboe@...cle.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	hugh@...itas.com, nickpiggin@...oo.com.au
Subject: Re: [patch 1/2] mm: dont clear PG_uptodate in invalidate_complete_page2()

On Wed, Jun 25, 2008 at 05:59:14PM +0200, Miklos Szeredi (miklos@...redi.hu) wrote:
> > Page is locked of course, but invalidated, removed from all trees and
> > caches, i.e. grab, lock, check, unlock... invalidate, write into that
> > page should fail, but it will not, since page is uptodate and
> > prepare_write does not check mapping at all.
> 
> But callers do check after having locked the page.

Yes, it is possible to check mapping, but it does not exist and it is
correct, that there is no mapping - we are just writing into page in
ram, kind of loop device, but without binding page into mapping.
And mapping itself is used just for its operations.

> > > > Instead of returning error when reading from invalid page, now you
> > > > return old content of it?
> > > 
> > > No, instead of returning a short count, it is now returning old
> > > content.
> > 
> > Or instead of returning error or zero and relookup page eventually,
> > which can already contain new data, we get old data.
> 
> Umm, it doesn't make any sense to try to always get fresh data.  If
> you do read() on a file, the data may become old and invalid a
> millisecond after the read finished.  We can't and needn't do anything
> about this.

Page reading from disk is atomic in respect that page is always locked,
now readpage(s) may not be called in some cases...

-- 
	Evgeniy Polyakov
--
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/