linux-kernel - Re: [PATCH] mm: avoid livelock on !__GFP

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: <alpine.DEB.2.00.1110251513520.26017@chino.kir.corp.google.com>
Date:	Tue, 25 Oct 2011 15:18:15 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Mel Gorman <mgorman@...e.de>
cc:	Colin Cross <ccross@...roid.com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org
Subject: Re: [PATCH] mm: avoid livelock on !__GFP_FS allocations

On Tue, 25 Oct 2011, Mel Gorman wrote:

> That said, it will be difficult to remember why checking __GFP_NOFAIL in
> this case is necessary and someone might "optimitise" it away later. It
> would be preferable if it was self-documenting. Maybe something like
> this? (This is totally untested)
> 

__GFP_NOFAIL _should_ be optimized away in this case because all he's 
passing is __GFP_WAIT | __GFP_NOFAIL.  That doesn't make any sense unless 
all you want to do is livelock.

__GFP_NOFAIL doesn't mean the page allocator would infinitely loop in all 
conditions.  That's why GFP_ATOMIC | __GFP_NOFAIL actually fails, and I 
would argue that __GFP_WAIT | __GFP_NOFAIL should fail as well since it's 
the exact same condition except doesn't have access to the extra memory 
reserves.

Suspend needs to either set __GFP_NORETRY to avoid the livelock if it's 
going to disable all means of memory reclaiming or freeing in the page 
allocator.  Or, better yet, just make it GFP_NOWAIT.
--
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/