On Mon 2020-10-05 20:35:59, Guenter Roeck wrote:
> On 10/5/20 7:59 PM, Sergey Senozhatsky wrote:
> > On (20/05/22 12:00), Petr Mladek wrote:
> >> On Fri 2020-05-22 16:53:06, Shreyas Joshi wrote:
> >>> If uboot passes a blank string to console_setup then it results in a
> >>> trashed memory.
> >>> Ultimately, the kernel crashes during freeing up the memory. This fix
> >>> checks if there
> >>> is a blank parameter being passed to console_setup from uboot.
> >>> In case it detects that the console parameter is blank then
> >>> it doesn't setup the serial device and it gracefully exits.
> >>>
> > Petr, this patch's causing regressions for us. We use blank console= boot
> > param to bypass dts. It appears that it'd be better to revert the change.
> >
> Not just to bypass dts, it was also possible to use console= to disable
> consoles
> passed as config option, as well as other default console options. A quick
> test
> confirms that this affects all platforms/architectures, not just Chromebooks.
> Prior to this patch, it was possible to disable a default console with an
> empty "console=" parameter. This is no longer possible. This means that
> this patch results in a substantial (and, as far as I can see, completely
> undiscussed) functionality change.
Where is this behavior documented, please?
I do not see it anywhere (documentation, git log, google) and it is far from
obvious from the code. It seems that any random string would do the
same job, e.g. console=none.
Of course, we need to restore the original behavior when it breaks
existing systems. But I want to be sure that there is no better
solution.
And it makes perfect sense to disable all consoles or drop all defined
by dts. But I would prefer to make it more obvious way, for
example by parameters like:
+ console=none
+ no-console
+ no-dtd-console
+ no-default-console
JFYI, the console= parameter handling is a real historical mess. We are
always surprised what undefined behavior people depend on. For
example, see:
+ commit 33225d7b0ac9903c5701b ("printk: Correctly set CON_CONSDEV
even when preferred console was not registered")
+ commit e369d8227fd211be3624 ("printk: Fix preferred console
selection with multiple matches")
> I don't understand why (yet), but the patch also causes regressions with
> seemingly unrelated functionality, specifically with dm-verity on at least
> one Chromebook platform. I filed crbug.com/1135157 to track the problem,
> and reverted the patch from all our stable releases immediately after
> the last round of stable release merges.
>
> On a side note, I don't see the problem presumably fixed with this
> patch in any of my tests.
Console drivers might provide a custom match() callback to handle
various aliases. I guess that some driver wrongly matches the empty
string stored in the array of preferred consoles.
There are likely other ways to fix the original problem.
Best Regards,
Petr
