linux-kernel - Re: [PATCH] Revert "kmemleak: allow to coexist with fault injection"

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: <20190716200715.GA14663@dhcp22.suse.cz>
Date:   Tue, 16 Jul 2019 22:07:15 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Qian Cai <cai@....pw>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, catalin.marinas@....com,
        dvyukov@...gle.com, rientjes@...gle.com, willy@...radead.org,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "kmemleak: allow to coexist with fault injection"

On Tue 16-07-19 15:21:17, Qian Cai wrote:
[...]
> Thanks to this commit, there are allocation with __GFP_DIRECT_RECLAIM that
> succeeded would keep trying with __GFP_NOFAIL for kmemleak tracking object
> allocations.

Well, not really. Because low order allocations with
__GFP_DIRECT_RECLAIM basically never fail (they keep retrying) even
without GFP_NOFAIL because that flag is actually to guarantee no
failure. And for high order allocations the nofail mode is actively
harmful. It completely changes the behavior of a system. A light costly
order workload could put the system on knees and completely change the
behavior. I am not really convinced this is a good behavior of a
debugging feature TBH.

> Otherwise, one kmemleak object allocation failure would kill the
> whole kmemleak.

Which is not great but quite likely a better than an unpredictable MM
behavior caused by NOFAIL storms. Really, this NOFAIL patch is a
completely broken behavior. There shouldn't be much discussion about
reverting it. I would even argue it shouldn't have been merged in the
first place. It doesn't have any acks nor reviewed-bys while it abuses
__GFP_NOFAIL which is generally discouraged to be used.

Thanks!
-- 
Michal Hocko
SUSE Labs