Re: [PATCH tty 0/1] Make 8250 deferred MSR handling LAZY

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Sep 21, 2026 at 12:07:46PM +0206, John Ogness wrote:
> Hi Greg, Jiri,
> 
> On 2026-08-28, John Ogness <john.ogness@linutronix.de> wrote:
> > There was a report and follow-up discussion [0] about a problem
> > using regular irq_work queuing on some platforms when entering
> > cpuidle. To circumvent this problem, all irq_work for printk will
> > become IRQ_WORK_LAZY [1].
> >
> > The 8250 console driver uses irq_work to defer MSR handling during
> > atomic printing. This means it is vulnerable to the same problem if,
> > for example, a WARN() is hit while entering cpuidle on one of the
> > affected platforms.
> >
> > Avoid the problem for deferred MSR handling by changing
> > console_msr_work to IRQ_WORK_LAZY.
> 
> Any chance of getting this into 7.3? A similar patch went into 7.3-rc3
> for printk:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/kernel/printk?id=560f4deda32785e260056200f8bb911c475c5b88
> 
> Or do I need to send a v2 with an updated commit message? I could
> rephrase it similar to the related printk commit. Something like this:
> 
> Change console_msr_work (defers MSR handling) to be IRQ_WORK_LAZY,
> thus not raising an IRQ upon irq_work queuing. The irq_work is then
> handled on the next kernel tick. This additional delay is acceptable
> because the MSR handling also occurs in the an interrupt handler, if
> mctrl is queried, and during console resume. Using IRQ_WORK_LAZY has
> the benefit of not needing to raise an IRQ for each line of atomic
> console printing when modem control is active.
> 
> On a side note, the Tegra20 and Tegra30 platforms can hang if an
> irq_work IRQ is raised while entering cpuidle states. This problem
> was reproducible by performing atomic printing while entering cpuidle.
> So this change also provides a workaround for these platforms (as
> long as they are not running tickless).

An updated changelog would be great, then I can take it for 7.3-final
easier.

thanks,

greg k-h