linux-kernel - Re: [PATCH 1/2] mm: Take all anon_vma locks in anon_vma

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:	Mon, 3 May 2010 20:13:40 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	akpm@...ux-foundation.org, Mel Gorman <mel@....ul.ie>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 1/2] mm: Take all anon_vma locks in anon_vma_lock

> > Btw, Mel's patch doesn't really match the description of 2/2. 2/2 says
> > that all pages must always be findable in rmap. Mel's patch seems to
> > explicitly say "we want to ignore that thing that is busy for execve". Are
> > we just avoiding a BUG_ON()? Is perhaps the BUG_ON() buggy?
> 
> I have no good answer to this question.
> 
> Mel?  Andrea?

If try_to_unmap is allowed to establish the migration pte, then such
pte has to remain reachable through rmap_walk at all times after that,
or migration_entry_wait will crash because it notices the page has
been migrated already (PG_lock not set) but there is still a migration
pte established. (remove_migration_pte like split_huge_page isn't
allowed to fail finding all migration ptes mapping a page during the
rmap walk)

It's not false positive BUG_ON if that's what you mean, removing the
BUG_ON would still lead to infinite hang waiting on a migration pte
that shouldn't be there anymore.
--
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/