linux-kernel - Re: [PATCH] char/random: silence a lockdep splat with printk()

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Message-ID: <20191205010055.GO93017@google.com>
Date:   Thu, 5 Dec 2019 10:00:55 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Qian Cai <cai@....pw>
Cc:     tytso@....edu, Arnd Bergmann <arnd@...db.de>,
        gregkh@...uxfoundation.org, sergey.senozhatsky.work@...il.com,
        pmladek@...e.com, rostedt@...dmis.org,
        Catalin Marinas <catalin.marinas@....com>, will@...nel.org,
        dan.j.williams@...el.com, peterz@...radead.org, longman@...hat.com,
        tglx@...utronix.de, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] char/random: silence a lockdep splat with printk()

Hi,

On (19/12/03 13:46), Qian Cai wrote:
> > On Nov 13, 2019, at 4:16 PM, Qian Cai <cai@....pw> wrote:
> > 
> > From: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
> > 
> > Sergey didn't like the locking order,
> > 
> > uart_port->lock  ->  tty_port->lock
> > 
> > uart_write (uart_port->lock)
> >  __uart_start
> >    pl011_start_tx
> >      pl011_tx_chars
> >        uart_write_wakeup
> >          tty_port_tty_wakeup
> >            tty_port_default
> >              tty_port_tty_get (tty_port->lock)
> > 
> > but those code is so old, and I have no clue how to de-couple it after
> > checking other locks in the splat. There is an onging effort to make all
> > printk() as deferred, so until that happens, workaround it for now as a
> > short-term fix.
> 
> Sergey, could we have a ACK from you so Ted might be able to merge?

Not sure if I can ACK it, but overall it makes sense to use deferred
printk there.

[..]
> 
> > [cai@....pw: add a commit log.]
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
> > Signed-off-by: Qian Cai <cai@....pw>
> > ---
> > 
> > Sergey, please let us know if you are fine with the Signed-off-by.

A 'Reviewed-by' will suffice.

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

	-ss