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Message-ID: <20220620122904.30c06c4e@thinkpad>
Date: Mon, 20 Jun 2022 12:29:04 +0200
From: Marek Behún <kabel@...nel.org>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: John Ogness <john.ogness@...utronix.de>,
Petr Mladek <pmladek@...e.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
linux-kernel@...r.kernel.org
Subject: Re: Boot stall regression from "printk for 5.19" merge
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
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