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Date:   Mon, 20 Jun 2022 12:29:04 +0200
From:   Marek =?UTF-8?B?QmVow7pu?= <kabel@kernel.org>
To:     Sergey Senozhatsky <senozhatsky@chromium.org>
Cc:     John Ogness <john.ogness@linutronix.de>,
        Petr Mladek <pmladek@suse.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: Boot stall regression from "printk for 5.19" merge
Message-ID: <20220620122904.30c06c4e@thinkpad>
In-Reply-To: <YrBIURn7lxykWghw@google.com>
References: <20220619204949.50d9154d@thinkpad>
        <YrAEUM20n3Rc4aOn@google.com>
        <20220620120234.5a65ac97@thinkpad>
        <YrBIURn7lxykWghw@google.com>
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On Mon, 20 Jun 2022 19:13:37 +0900
Sergey Senozhatsky <senozhatsky@chromium.org> wrote:

> On (22/06/20 12:02), Marek Beh=C3=BAn wrote:
> > > On (22/06/19 20:49), Marek Beh=C3=BAn wrote:
> > > [..] =20
> > > > 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 man=
gled
> > > > for a while (the serial console spits garbage characters).   =20
> > >=20
> > > 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). =20
> >=20
> > This indeed makes the problem go away... =20
>=20
> Oh... OK. Didn't expect that :)
>=20
> > > > The garbage example:
> > > >=20
> > > >   ...
> > > >   [    0.920951] raid6: using neon recovery algorithm
> > > >   [    0.921228] iommu: Default domain type: Translated
> > > >   %
> > > >=20
> > > >           gb@k+cFL/[    4.954974] DSA: tree 0 setup
> > > >   [    4.955286] cfg80211: Loading compiled-in X.509 certificates f=
or regulatory database   =20
> > >=20
> > > 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. =20
> >=20
> > Maybe multiple threads are writing to serial registers, or something...=
 =20
>=20
> 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 =3D "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