Re: [PATCH v2 1/1] fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

[Miklos Szeredi <miklos@szeredi.hu>]

On Tue, 6 Jan 2026 at 11:05, David Hildenbrand (Red Hat)
<david@kernel.org> wrote:

> > So I understand your patch fixes the regression with suspend blocking but I
> > don't have a high confidence we are not just starting a whack-a-mole game

Joanne did a thorough analysis, so I still have hope.  Missing a case
in such a complex thing is not unexpected.

> Yes, I think so, and I think it is [1] not even only limited to
> writeback [2].

You are referring to DoS against compaction?

It is a much more benign issue, since compaction will just skip locked
pages, AFAIU (wasn't always so:
https://lore.kernel.org/all/1288817005.4235.11393.camel@nimitz/).

Not saying it shouldn't be fixed, but it should be a separate discussion.

> To handle the bigger picture (I raised another problematic instance in
> [4]): I don't know how to handle that without properly fixing fuse. Fuse
> folks should really invest some time to solve this problem for good.

Fixing it generically in fuse would necessarily involve bringing back
some sort of temp buffer.  The performance penalty could be minimized,
but complexity is what really hurts.

Maybe doing whack-a-mole results in less mess overall :-/

> As a big temporary kernel hack, we could add a
> AS_ANY_WAITING_UTTERLY_BROKEN and simply refuse to wait for writeback
> directly inside folio_wait_writeback() -- not arbitrarily skipping it in
> callers -- and possibly other places (readahead, not sure). That would
> restore the old behavior.

No it wouldn't, since the old code had surrogate methods for waiting
on outstanding writes, which were called on fsync, etc.

Thanks,
Miklos