linux-kernel - Re: 4.14 backport request for dbdda842fe96f: "printk: Add console owner and waiter logic to load balance console writes"

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Message-ID: <20181213095931.24qovurhtpa3jxzl@pathway.suse.cz>
Date:   Thu, 13 Dec 2018 10:59:31 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Daniel Wang <wonderfly@...gle.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sasha Levin <sashal@...nel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>, stable@...r.kernel.org,
        Alexander.Levin@...rosoft.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        byungchul.park@....com, dave.hansen@...el.com, hannes@...xchg.org,
        jack@...e.cz, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Mel Gorman <mgorman@...e.de>, mhocko@...nel.org, pavel@....cz,
        penguin-kernel@...ove.sakura.ne.jp,
        Peter Zijlstra <peterz@...radead.org>, tj@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>, vbabka@...e.cz,
        Cong Wang <xiyou.wangcong@...il.com>,
        Peter Feiner <pfeiner@...gle.com>
Subject: Re: 4.14 backport request for dbdda842fe96f: "printk: Add console
 owner and waiter logic to load balance console writes"

On Wed 2018-12-12 18:39:42, Daniel Wang wrote:
> > Additionally, for dbdda842fe96f to work as expected we really
> need fd5f7cde1b85d4c. Otherwise printk() can schedule under
> console_sem and console_owner, which will deactivate the "load
> balance" logic.
> 
> It looks like fd5f7cde1b85d4c got into 4.14.82 that was released last month.
> 
> On Wed, Dec 12, 2018 at 6:27 PM Sergey Senozhatsky
> <sergey.senozhatsky.work@...il.com> wrote:
> >
> > On (12/12/18 16:40), Daniel Wang wrote:
> > > In case this was buried in previous messages, the commit I'd like to
> > > get backported to 4.14 is dbdda842fe96f: printk: Add console owner and
> > > waiter logic to load balance console writes. But another followup
> > > patch that fixes a bug in that patch is also required. That is
> > > c14376de3a1b: printk: Wake klogd when passing console_lock owner.
> >
> > Additionally, for dbdda842fe96f to work as expected we really
> > need fd5f7cde1b85d4c. Otherwise printk() can schedule under
> > console_sem and console_owner, which will deactivate the "load
> > balance" logic.

To make it clear. Please, make sure that the following commits are
backported together:

+ dbdda842fe96f8932ba ("printk: Add console owner and waiter
		logic to load balance console writes")
+ 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")


I generated this list from git log using "Fixes:" tag. It seems
to mention all commits dicussed above.

Best Regards,
Petr