Re: Bug caused by 53965c79c2db (USB: Fix device driver race)

From: Alan Stern <stern@rowland.harvard.edu>
To: Pany <pany@fedoraproject.org>
Cc: Bastien Nocera <hadess@hadess.net>,
	"M. Vefa Bicakci" <m.v.b@runbox.com>,
	linux-usb@vger.kernel.org
Subject: Re: Bug caused by 53965c79c2db (USB: Fix device driver race)
Date: Mon, 19 Oct 2020 13:40:28 -0400	[thread overview]
Message-ID: <20201019174028.GF898631@rowland.harvard.edu> (raw)
In-Reply-To: <CAE3RAxvNUvzqKT+GK3A4cQ7Tm_tFRQJKfJ01r0ic-5066fikDA@mail.gmail.com>

On Mon, Oct 19, 2020 at 09:36:00AM +0000, Pany wrote:
> On Sat, Oct 17, 2020 at 8:02 PM Alan Stern <stern@rowland.harvard.edu> wrote:
> >
> > On Sat, Oct 17, 2020 at 04:07:11PM +0000, Pany wrote:
> > > Hi,
> > >
> > > I installed fedora 32 into an SD card, with which I booted my Macbook.
> > > It had worked well before, until I upgraded the kernel from 5.8.5 to
> > > 5.8.6 [1].
> > >
> > > With kernel-5.8.6-200.fc32.x86_64.rpm [2] installed, the boot process
> > > would be stuck at "A start job is running for
> > > /dev/mapper/fedora_localhost_--live-home (<time> / no limit)" (See the
> > > photo of screen [3]).
> > >
> > > By appending "systemd.debug-shell=1" to the kernel cmdline, I saved
> > > the journal [4].
> > >
> > > This issue has been bisected to commit
> > > 53965c79c2dbdc898ffc7fdbab37e920594f5e14 ("USB: Fix device driver
> > > race")
> > >
> > > If I revert this commit, the kernel 5.8.6 would boot successfully.
> >
> > This should have been fixed in 5.8.14 or 5.8.15 (5.8.14 was released on
> > the same day that the fix was installed; I'm not sure which came first).
> > At any rate it certainly should work with the most recent 5.8.y kernel.
> >
> > Alan Stern
> 
> I tried, but neither 5.8.14 nor 5.8.15 worked for me.

Hmmm.  Looking at the system log you captured, it appears that the 
problem the SD card reader's driver getting reprobed incorrectly.  The 
details aren't clear, but the log shows the device getting probed twice, 
once as sdb and once as sdc.  If the system tried to mount one of the 
sdb partitions as the root, and then sdb disappeared, that could explain 
what you see.

I don't know why this is happening.  But you can try adding some 
debugging messages of your own.  In drivers/usb/core/driver.c, the 
routine __usb_bus_reprobe_drivers() should never reach the line that 
calls device_reprobe() unless the USBIP or apple-mfi-fastcharge driver 
is installed -- and neither of those should be involved with the card 
reader device.  You can add a line saying:

	dev_info(dev, "new driver %s\n", new_udriver->name);

at that point and see what it produces in the log.

Alan Stern