linux-kernel - Re: [PATCH 02/18] serial: sc16is7xx: fix invalid sc16is7xx

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Date: Thu, 21 Dec 2023 10:56:39 -0500
From: Hugo Villeneuve <hugo@...ovil.com>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: gregkh@...uxfoundation.org, jirislaby@...nel.org, jringle@...dpoint.com,
 kubakici@...pl, phil@...pberrypi.org, bo.svangard@...eddedart.se,
 linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org, Hugo Villeneuve
 <hvilleneuve@...onoff.com>, stable@...r.kernel.org, Yury Norov
 <yury.norov@...il.com>
Subject: Re: [PATCH 02/18] serial: sc16is7xx: fix invalid sc16is7xx_lines
 bitfield in case of probe error

On Wed, 20 Dec 2023 17:40:42 +0200
Andy Shevchenko <andriy.shevchenko@...el.com> wrote:

> On Tue, Dec 19, 2023 at 12:18:46PM -0500, Hugo Villeneuve wrote:
> > From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> > 
> > If an error occurs during probing, the sc16is7xx_lines bitfield may be left
> > in a state that doesn't represent the correct state of lines allocation.
> > 
> > For example, in a system with two SC16 devices, if an error occurs only
> > during probing of channel (port) B of the second device, sc16is7xx_lines
> > final state will be 00001011b instead of the expected 00000011b.
> > 
> > This is caused in part because of the "i--" in the for/loop located in
> > the out_ports: error path.
> > 
> > Fix this by checking the return value of uart_add_one_port() and set line
> > allocation bit only if this was successful. This allows the refactor of
> > the obfuscated for(i--...) loop in the error path, and properly call
> > uart_remove_one_port() only when needed, and properly unset line allocation
> > bits.
> > 
> > Also use same mechanism in remove() when calling uart_remove_one_port().
> 
> Yes, this seems to be the correct one to fix the problem described in
> the patch 1. I dunno why the patch 1 even exists.

Hi,
this will indeed fix the problem described in patch 1.

However, if I remove patch 1, and I simulate the same probe error as
described in patch 1, now we get stuck forever when trying to 
remove the driver. This is something that I observed before and
that patch 1 also corrected.

The problem is caused in sc16is7xx_remove() when calling this function

    kthread_flush_worker(&s->kworker);

I am not sure how best to handle that without patch 1.

Hugo Villeneuve