linux-kernel - Re: [PATCH 2/2] mm: drop PF_MEMALLOC

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: <ZsyyqxSv3-IbaAAO@tiehlicka>
Date: Mon, 26 Aug 2024 18:51:55 +0200
From: Michal Hocko <mhocko@...e.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>, Yafang Shao <laoar.shao@...il.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>, jack@...e.cz,
	Christian Brauner <brauner@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-bcachefs@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: drop PF_MEMALLOC_NORECLAIM

On Mon 26-08-24 14:59:29, Matthew Wilcox wrote:
> On Mon, Aug 26, 2024 at 10:47:13AM +0200, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@...e.com>
> > 
> > There is no existing user of the flag and the flag is dangerous because
> > a nested allocation context can use GFP_NOFAIL which could cause
> > unexpected failure. Such a code would be hard to maintain because it
> > could be deeper in the call chain.
> > 
> > PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1]
> > that such a allocation contex is inherently unsafe if the context
> > doesn't fully control all allocations called from this context.
> 
> Wouldn't a straight-up revert of eab0af905bfc be cleaner?  Or is there
> a reason to keep PF_MEMALLOC_NOWARN?

I wanted to make it PF_MEMALLOC_NORECLAIM specific. I do not have a
strong case against PF_MEMALLOC_NOWARN TBH. It is a hack because the
scope is claiming something about all allocations within the scope
without necessarily knowing all of them (including potential future
changes). But NOWARN is not really harmful so I do not care strongly.

If a plan revert is preferably, I will go with it.
-- 
Michal Hocko
SUSE Labs