linux-kernel - Re: Boot stall regression from "printk for 5.19" merge

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Date:   Mon, 20 Jun 2022 13:01:28 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Marek Behún <kabel@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Boot stall regression from "printk for 5.19" merge

+Cc: Ilpo, a new maintainer for the driver

On Mon, Jun 20, 2022 at 12:46 PM Marek Behún <kabel@...nel.org> wrote:
>
> On Mon, 20 Jun 2022 19:13:37 +0900
> Sergey Senozhatsky <senozhatsky@...omium.org> wrote:
>
> > On (22/06/20 12:02), Marek Behún wrote:
> > > > On (22/06/19 20:49), Marek Behún wrote:
> > > > [..]
> > > > > causes a regression on arm64 (Marvell CN9130-CRB board) where the
> > > > > system boot freezes in most cases (and is unusable until restarted by
> > > > > watchdog), or, in some cases boots, but the console output gets mangled
> > > > > for a while (the serial console spits garbage characters).
> > > >
> > > > Can you please try disabling console kthreads and see how the boot
> > > > process goes? Just `return 0` from printk_activate_kthreads() (I think
> > > > this should do the trick).
> > >
> > > This indeed makes the problem go away...
> >
> > Oh... OK. Didn't expect that :)
> >
> > > > > The garbage example:
> > > > >
> > > > >   ...
> > > > >   [    0.920951] raid6: using neon recovery algorithm
> > > > >   [    0.921228] iommu: Default domain type: Translated
> > > > >   %
> > > > >
> > > > >           gb@...FL/[    4.954974] DSA: tree 0 setup
> > > > >   [    4.955286] cfg80211: Loading compiled-in X.509 certificates for regulatory database
> > > >
> > > > This is pretty suspicious. I don't see how console kthreads would
> > > > corrupt the output. I suspect that something else is going on, some
> > > > memory corruption, etc.
> > >
> > > Maybe multiple threads are writing to serial registers, or something...
> >
> > That's possible. Console drivers usually should grab port->lock for
> > write(), but maybe something is missing in the driver you use. What
> > console driver are you using?
>
> compatible = "snps,dw-apb-uart", so drivers/tty/serial/8250/8250_dw.c
>
> seems that the function dw8250_serial_out() does not use the spinlock...
>
> Marek



-- 
With Best Regards,
Andy Shevchenko