linux-kernel - Re: [PATCH AUTOSEL for 4.15 019/189] printk: Add console owner and waiter logic to load balance console writes

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Date:   Sun, 15 Apr 2018 14:34:52 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     Petr Mladek <pmladek@...e.com>
CC:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Byungchul Park <byungchul.park@....com>,
        Tejun Heo <tj@...nel.org>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH AUTOSEL for 4.15 019/189] printk: Add console owner and
 waiter logic to load balance console writes

On Mon, Apr 09, 2018 at 10:15:35AM +0200, Petr Mladek wrote:
>On Mon 2018-04-09 00:16:59, Sasha Levin wrote:
>> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
>>
>> [ Upstream commit dbdda842fe96f8932bae554f0adf463c27c42bc7 ]
>>
>> This patch implements what I discussed in Kernel Summit. I added
>> lockdep annotation (hopefully correctly), and it hasn't had any splats
>> (since I fixed some bugs in the first iterations). It did catch
>> problems when I had the owner covering too much. But now that the owner
>> is only set when actively calling the consoles, lockdep has stayed
>> quiet.
>
>I do not think that this is a material for stable backports. Yes, it
>is a fix but it is not trivial. There are already 3 follow up commits:
>
>c162d5b4338d72deed6 ("printk: Hide console waiter logic into helpers")
>fd5f7cde1b85d4c8e09 ("printk: Never set console_may_schedule in
>		console_trylock()")
>c14376de3a1befa70d9 ("printk: Wake klogd when passing console_lock owner")
>
>One is just a code clean up but the other two are changes/fixes that
>should go together with Steven's patch.
>
>These changes tries to prevent softlockups. It is a problem that is
>being discussed for years. We are still waiting for feedback to see if
>more changes will be necessary. IMHO, there is no reason to hurry and
>backport it everywhere.
>
>Best Regards,
>Petr

I'll remove it, thanks Petr!