linux-kernel - Re: [RFC v2 PATCH] mm/percpu.c: fix panic triggered by BUG

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, 12 Oct 2016 14:41:12 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     zijun_hu <zijun_hu@...o.com>
Cc:     tj@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        zijun_hu@....com, cl@...ux.com
Subject: Re: [RFC v2 PATCH] mm/percpu.c: fix panic triggered by BUG_ON()
 falsely

On Tue, 11 Oct 2016 22:00:28 +0800 zijun_hu <zijun_hu@...o.com> wrote:

> as shown by pcpu_build_alloc_info(), the number of units within a percpu
> group is educed by rounding up the number of CPUs within the group to
> @upa boundary, therefore, the number of CPUs isn't equal to the units's
> if it isn't aligned to @upa normally. however, pcpu_page_first_chunk()
> uses BUG_ON() to assert one number is equal the other roughly, so a panic
> is maybe triggered by the BUG_ON() falsely.
> 
> in order to fix this issue, the number of CPUs is rounded up then compared
> with units's, the BUG_ON() is replaced by warning and returning error code
> as well to keep system alive as much as possible.

Under what circumstances is the triggered?  In other words, what are
the end-user visible effects of the fix?

I mean, this is pretty old code (isn't it?) so what are you doing that
triggers this?