Re: writeback completion soft lockup BUG in folio_wake_bit()

[Linus Torvalds <torvalds@linux-foundation.org>]

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.

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...

               Linus