Re: writeback completion soft lockup BUG in folio_wake_bit()

[Dan Williams <dan.j.williams@intel.com>]

Linus Torvalds wrote:
> On Mon, Oct 24, 2022 at 12:39 PM Tim Chen <tim.c.chen@linux.intel.com> wrote:
> >
> > I do think that the original locked page on migration problem was fixed
> > by commit 9a1ea439b16b. Unfortunately the customer did not respond to
> > us when we asked them to test their workload when that patch went
> > into the mainline.
> 
> Oh well.
> 
> > I don't have objection to Matthew's fix to remove the bookmark code,
> > now that it is causing problems with this scenario that I didn't
> > anticipate in my original code.
> 
> I'd really like to avoid *another* "we can't actually verify that this
> helps" change in this area, so I'm hoping that the reporter that Dan
> was talking to could test that patch.

Oh, sorry, I had typed up that reply and contacted Tim offline, but
forgot to send, now sent.

> Otherwise we're kind of going back-and-forth based on "this might fix
> things", which just feels really fragile and reminds me of the bad old
> days when we had the "one step forward, two steps back" dance with
> some of the suspend/resume issues.
> 
> I realize that this code needs some extreme loads (and likely pretty
> special hardware too) to actually become problematic, so testing is
> _always_ going to be a bit of a problem, but still...