Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <CAJmjG2-RrG5XKeW1-+rN3C=F6bZ-L3=YKhCiQ_muENDTzm_Ofg@mail.gmail.com>
 <20181002212327.7aab0b79@vmware.local.home> <20181003091400.rgdjpjeaoinnrysx@pathway.suse.cz>
 <CAJmjG2_4JFA=qL-d2Pb9umUEcPt9h13w-g40JQMbdKsZTRSZww@mail.gmail.com>
 <20181003133704.43a58cf5@gandalf.local.home> <CAJmjG291w2ZPRiAevSzxGNcuR6vTuqyk6z4SG3xRsbaQh5U3zQ@mail.gmail.com>
 <20181004074442.GA12879@jagdpanzerIV> <20181004083609.kcziz2ynwi2w7lcm@pathway.suse.cz>
 <20181004085515.GC12879@jagdpanzerIV> <CAJmjG2-e6f6p=pE5uDECMc=W=81SYyGCmoabrC1ePXwL5DFdSw@mail.gmail.com>
 <20181022100952.GA1147@jagdpanzerIV>
In-Reply-To: <20181022100952.GA1147@jagdpanzerIV>
From:   Daniel Wang <wonderfly@google.com>
Date:   Thu, 1 Nov 2018 09:05:27 -0700
Message-ID: <CAJmjG2-c4e_1999n0OV5B9ABG9rF6n=myThjgX+Ms1R-vc3z+A@mail.gmail.com>
Subject: Re: 4.14 backport request for dbdda842fe96f: "printk: Add console
 owner and waiter logic to load balance console writes"
To:     sergey.senozhatsky.work@gmail.com
Cc:     Petr Mladek <pmladek@suse.com>, rostedt@goodmis.org,
        stable@vger.kernel.org, Alexander.Levin@microsoft.com,
        akpm@linux-foundation.org, byungchul.park@lge.com,
        dave.hansen@intel.com, hannes@cmpxchg.org, jack@suse.cz,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Mel Gorman <mgorman@suse.de>, mhocko@kernel.org, pavel@ucw.cz,
        penguin-kernel@i-love.sakura.ne.jp, peterz@infradead.org,
        tj@kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Peter Feiner <pfeiner@google.com>
Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256;
        boundary="0000000000001a71ef05799c97a9"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

--0000000000001a71ef05799c97a9
Content-Type: text/plain; charset="UTF-8"

On Mon, Oct 22, 2018 at 3:10 AM Sergey Senozhatsky
<sergey.senozhatsky.work@gmail.com> wrote:

> Another deadlock scenario could be the following one:
>
>         printk()
>          console_trylock()
>           down_trylock()
>            raw_spin_lock_irqsave(&sem->lock, flags)
>             <NMI>
>              panic()
>               console_flush_on_panic()
>                console_trylock()
>                 raw_spin_lock_irqsave(&sem->lock, flags)        // deadlock
>
> There are no patches addressing this one at the moment. And it's
> unclear if you are hitting this scenario.

I am not sure, but Steven's patches did make the deadlock I saw go away...

>
>
> > I see that Sergey had sent an RFC series for similar things. Are those
> > trying to solve the deadlock problem in a different way?
>
> Umm, I wouldn't call it "another way". It turns non-reentrant serial
> consoles to re-entrable ones. Did you test patch [1] from that series
> on you environment, by the way?

A little swamped by other things lately but I'll run a test with it.
If it works, would you recommend taking your patch alone and not
bother taking Steven's (since as you mentioned above even with his
patches there's still possibility for other deadlocks) ?

>
> [1] lkml.kernel.org/r/20181016050428.17966-2-sergey.senozhatsky@gmail.com
>
>         -ss


-- 
Best,
Daniel

--0000000000001a71ef05799c97a9
Content-Type: application/pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
Content-Description: S/MIME Cryptographic Signature
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--0000000000001a71ef05799c97a9--