[scsi_generic] Bad media in DVD drive leads to enormous boot time since 6.5rc

[Koba Ko]

Hi Sune,
the maintainer has some comments on this series[0],
it's still not merged.

Ref. [0], https://lore.kernel.org/lkml/20230806170604.16143-11-james@equiv.tech/T/

Thanks
Koba Ko

On Wed, Sep 20, 2023 at 4:36 AM Sune Mølgaard <sune at molgaard.org> wrote:
>
> 25/07/2023 04:08+0200, I reported that 6.5-rc wouldn't boot, possibly due to UBSAN complaining about mpt3sas.
>
> Patches were since provided for mpt3sas that got rid of the UBSAN error messages, but non-boot (later discovered to "just" being that boot wouldn't complete until after ~1½ hours) remained.
>
> Just now, I discovered that the ~1½ hour boot time is unrelated to mpt3sas and is, instead, related to a quite specific set of circumstances:
>
> System has an optical media drive
>
> May even be specific to DVDRW  GUD0N
>
> The drive is loaded with a defective medium
>
> Disk is scratched, and for the longest time, I have been meaning to attempt a ddrescue but haven't gotten around to it
>
> Pre-6.5-rc, a seek error would be reported, and that was that.
>
> Since 6.5-rc, what happens instead, is that ATA speed negotiation will cycle between the various possible speeds, precluding the udevd queue from emptying, hence tying up systemd-udevd, for approximately 1½ hours, before boot eventually completes.
>
> Pre-6.5-rc kernels still boot in reasonable time, as does 6.6-rc2 (and probably any in-between) if the drive tray is open during boot, precluding the bad medium from being attempted to be read.
>
> Now, with optical drives going out of fashion and, presumably, with having defective media in such a drive during boot being even rarer, the likelihood of widespread impact is low, but given the extreme impact (boot time goes from <1m to ~1½h), and given the obvious wrongness of the behaviour in this scenario, I do think a fix would be in order.
>
> I should obviously do a git bisect at some point, but until I have time for that, if someone happens to have an idea as to what commit might have effected the new behaviour, I shall be happy to test patches in the mean time.
>
> /sune
>
> NB: Koba Ko is Cc: since he responded to the 25/07 email. Koba, the UBSAN patches seem just perfect, and the boot problem turned out to be completely unrelated.