linux-kernel - Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

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Date:   Thu, 10 Oct 2019 14:12:01 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Peter Oberparleiter <oberpar@...ux.ibm.com>, Qian Cai <cai@....pw>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Petr Mladek <pmladek@...e.com>, akpm@...ux-foundation.org,
        sergey.senozhatsky.work@...il.com, rostedt@...dmis.org,
        peterz@...radead.org, linux-mm@...ck.org,
        john.ogness@...utronix.de, david@...hat.com,
        linux-kernel@...r.kernel.org,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

On (10/09/19 16:26), Michal Hocko wrote:
> On Wed 09-10-19 15:56:32, Peter Oberparleiter wrote:
> [...]
> > A generic solution would be preferable from my point of view though,
> > because otherwise each console driver owner would need to ensure that any
> > lock taken in their console.write implementation is never held while
> > memory is allocated/released.
>
> Considering that console.write is called from essentially arbitrary code
> path IIUC then all the locks used in this path should be pretty much
> tail locks or console internal ones without external dependencies.

That's a good expectation, but I guess it's not always the case.

One example might be NET console - net subsystem locks, net device
drivers locks, maybe even some MM locks (skb allocations?).

But even more "commonly used" consoles sometimes break that
expectation. E.g. 8250

serial8250_console_write()
 serial8250_modem_status()
  wake_up_interruptible()

And so on.

	-ss