linux-kernel - Re: [PATCH 0/2] Make printk_deferred() work properly before percpu setup is done

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: <20200327024500.GA211096@google.com>
Date:   Fri, 27 Mar 2020 11:45:00 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-kernel@...r.kernel.org, Dennis Zhou <dennis@...nel.org>,
        Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH 0/2] Make printk_deferred() work properly before percpu
 setup is done

On (20/03/26 17:32), Jann Horn wrote:
> While I was doing some development work, I noticed that if you call
> printk_deferred() before percpu setup has finished, stuff breaks, and
> e.g. "dmesg -w" fails to print new messages.
> 
> This happens because writing to percpu memory before percpu
> initialization is done causes the modified percpu memory to be
> propagated from the boot CPU to all the secondary CPUs; and both the
> printk code as well as the irq_work implementation use percpu memory.
> 
> I think that printk_deferred() ought to work even before percpu
> initialization, since it is used by things like pr_warn_ratelimited()
> and the unwinder infrastructure. I'm not entirely sure though whether
> this is the best way to implement that, or whether it would be better to
> let printk_deferred() do something different if it is called during
> early boot.

Hi Jann,

I believe we have a patch for this issue

https://lore.kernel.org/lkml/20200303113002.63089-1-sergey.senozhatsky@gmail.com/

	-ss