linux-kernel - Re: [patch] drivers/zram: Don't disable preemption in zcomp_stream

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: <20161017142428.25dyxefk2arjeyfz@linutronix.de>
Date:   Mon, 17 Oct 2016 16:24:28 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Mike Galbraith <umgwanakikbuti@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [patch] drivers/zram: Don't disable preemption in
 zcomp_stream_get/put()

On 2016-10-16 05:14:22 [+0200], Mike Galbraith wrote:
> 
> In v4.7, the driver switched to percpu compression streams, disabling
> preemption (get/put_cpu_ptr()).  Use get/put_cpu_light() instead.

I am not convinced that this will work. Nothing prevents
zram_bvec_write() to be reentrant on the same CPU what I can tell from
browsing over the code and since it uses zstrm->buffer for compression
it can go wrong. Also I don't know if crypto's tfm handler can be used
in parallel for any ops (it usually does not work for crypto).

I suggest a local lock or a good reason why the this patch works.

Sebastian