On Sun, Sep 8, 2024 at 8:03 AM Damien Le Moal <dlemoal@xxxxxxxxxx> wrote:
>
> On 9/7/24 20:14, Richard W.M. Jones wrote:
> > On Sat, Sep 07, 2024 at 07:02:30PM +0800, Ming Lei wrote:
> >> BTW, the issue can be reproduced 100% by:
> >>
> >> echo "deadlock" > /sys/block/$ROOT_DISK/queue/scheduler
>
> This probably should be:
>
> echo "mq-deadline" > /sys/block/$ROOT_DISK/queue/scheduler
>
> and make sure that:
> 1) mq-deadline is compiled as a module
> 2) mq-deadline is not already used by a device (so not loaded already)
> 3) The mq-deadline module file is stored on the target device of the scheduler
> change
> 4) The mq-deadline module file is not already cahced in the page cache.
>
> For (4), you may want to do a "echo 3 > /proc/sys/vm/drop_caches" before trying
> to switch the scheduler.
>
> >
> > That doesn't reproduce it for me (reliably). Although I'm not
> > surprised as this bug has been _very_ tricky to reproduce! Sometimes
> > I think I have a definite reproducer, only for it to go away when some
> > tiny detail changes.
> >
> >>> This seems like the neatest (or shortest) fix so far, but doesn't it
> >>> "mix up layers" by checking elv_iosched_store?
> >>
> >> It is just one exception for 'scheduler' sysfs attribute wrt. freezing
> >> queue for storing, and the check can be done via the attribute
> >> name("scheduler") too.
> >
> > Fair enough.
> >
> > Rich.
> >
>
> --
> Damien Le Moal
> Western Digital Research
>
