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Date:   Mon, 20 Jun 2022 19:13:37 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     Marek =?iso-8859-1?Q?Beh=FAn?= <kabel@kernel.org>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        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: <YrBIURn7lxykWghw@google.com>
References: <20220619204949.50d9154d@thinkpad>
 <YrAEUM20n3Rc4aOn@google.com>
 <20220620120234.5a65ac97@thinkpad>
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On (22/06/20 12:02), Marek Beh?n wrote:
> > On (22/06/19 20:49), Marek Beh?n 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@k+cFL/[    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?