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

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Date:   Tue, 7 Jan 2020 16:07:24 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Qian Cai <cai@....pw>
Cc:     arnd@...db.de, gregkh@...uxfoundation.org,
        sergey.senozhatsky.work@...il.com, pmladek@...e.com,
        rostedt@...dmis.org, 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()

On Wed, Nov 13, 2019 at 04:16:25PM -0500, Qian Cai 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.

Applied, thanks.

					- Ted