Re: Since 6.10 - kernel oops/panics on G4 macmini due to change in drivers/ata/pata_macio.c

[Niklas Cassel <cassel@kernel.org>]

Hello Michael,

On Tue, Aug 13, 2024 at 10:32:36PM +1000, Michael Ellerman wrote:
> Niklas Cassel <cassel@kernel.org> writes:
> > Hello Jonáš, Kolbjørn,
> >
> > thank you for the report.
> >
> > On Tue, Aug 13, 2024 at 07:49:34AM +0200, Jonáš Vidra wrote:
> >> On Tue 13. Aug 2024 0:32:37 CEST, Kolbjørn Barmen wrote:
> >> > Ever since 6.10, my macmini G4 behaved unstable when dealing with lots of
> >> > I/O activity, such as sync'ing of Gentoo portage tree, unpacking kernel
> >> > source tarball, building large software packages (or kernel) etc.
> >> > 
> >> > After a bit of testing, and patient kernel rebuilding (while crashing) I
> >> > found the cuplit to be this commit/change
> >> > 
> >> > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/diff/?id=09fe2bfa6b83f865126ce3964744863f69a4a030
> >> 
> >> I've been able to reproduce this pata_macio bug on a desktop PowerMac G4
> >> with the 6.10.3 kernel version. Reverting the linked change
> >> ("ata: pata_macio: Fix max_segment_size with PAGE_SIZE == 64K") makes
> >> the errors go away.
> >
> > Michael, as the author of the this commit, could you please look into
> > this issue?
> 
> I can. My commit was really just working around the warning in the SCSI
> core which appeared after afd53a3d8528, it was supposed to just fix the
> warning without changing behaviour. Though obviously it did for 4KB
> PAGE_SIZE kernels.
> 
> I don't have easy access to my mac-mini so it would be helpful if you
> can test changes Jonáš and/or Kolbjørn.
> 
> > We could revert your patch, which appears to work for some users,
> > but that would again break setups with PAGE_SIZE == 64K.
> > (I assume that Jonáš and Kolbjørn are not building with PAGE_SIZE == 64K.)
> 
> Yes they are using 4K, it says so in the oops.
> 
> >> ------------[ cut here ]------------
> >> kernel BUG at drivers/ata/pata_macio.c:544!
> >
> > https://github.com/torvalds/linux/blob/v6.11-rc3/drivers/ata/pata_macio.c#L544
> >
> > It seems that the
> > while (sg_len) loop does not play nice with the new .max_segment_size.
> 
> Right, but only for 4KB kernels for some reason. Is there some limit
> elsewhere that prevents the bug tripping on 64KB kernels, or is it just
> luck that no one has hit it?

Have your tried running fio (flexible I/O tester), with reads with a very
large block sizes?

I would be surprised if it isn't possible to trigger the same bug with
64K page size.

max segment size = 64K
MAX_DCMDS = 256
256 * 64K = 16 MiB
What happens if you run fio with a 16 MiB blocksize?

Something like:
$ sudo fio --name=test --filename=/dev/sdX --direct=1 --runtime=60 --ioengine=io_uring --rw=read --iodepth=4 --bs=16M


Kind regards,
Niklas