Hi Jiri, Thanks for the follow-up. You responded faster than I could correct myself. On 2023-08-14, Jiri Slaby <jirislaby@xxxxxxxxxx> wrote: >>> The port lock is not always held when calling serial8250_clear_IER(). >>> When an oops is in progress, the lock is tried to be taken and when it >>> is not, a warning is issued: >> >> Yes, and that is a potential deadlock. The warning is correct. > > Could you elaborate on how can not-taking a lock be a potential > deadlock? I was wrong to say deadlock. The lockdep annotation is about interrupts being unintentionally left permanently disabled or being enabled while another CPU is transmitting. >>> Therefore, remove the annotation as it doesn't hold for all invocations. >> >> ... because those invocations are broken by design. > > Perhaps. But the system is crashing. Better to emit something without > the lock rather than nothing (and wait for the lock infinitely). I am not suggesting to wait infinitely. I am merely pointing out that the lockdep warning is legitimate. >>> The other option would be to make the lockdep test conditional on >>> 'oops_in_progress' Actually I find this suggestion more appropriate. It makes it clear that we are willing to take such risks and do not want to see the warnings in a panic situation. However, I would end up having to revert that change as well, so it really does not matter to me at this point. Either way I will be reverting this patch. >> The proper thing to do is to fix the invocation. The upcoming atomic >> console implementation for the 8250 does exactly that. > > So what does it do? The upcoming atomic consoles use a new type of synchronization to guard the IER register (priority-based spinning with timeouts). This allows us to make intelligent decisions about how and when to flush in a panic, rather than simply ignorning locks and hoping for the best. >> If this patch gets accepted (which it appears it will be), I will revert >> it in my series implementing the 8250 atomic console. > > That's fine as soon as the warning is not a problem. Yes, I am also fine with re-introducing the annotation together with the 8250 series. John
