Re: [PATCH RESEND V2 0/5] Fixes and cleanups to xarray

[Matthew Wilcox <willy@infradead.org>]

On Tue, Nov 12, 2024 at 03:05:51PM +0800, Kemeng Shi wrote:
> Patch 1 fixes the issue that xas_find_marked() will return a sibling entry
> to users when there is a race to replace old entry with small range with
> a new entry with bigger range. The kernel will crash if users use returned
> sibling entry as a valid entry.
> For example, find_get_entry() will crash if it gets a sibling entry from
> xas_find_marked() when trying to search a writeback folios.

You _think_ this can happen, or you've observed a crash where it _has_
happened?  I don't think it can happen due to the various locks we
have.  I'm not opposed to including this patch, but I don't think it
can happen today.

> Patch 3 fixes the issue that xas_pause() may skip some entry unepxectedly
> after xas_load()(may be called in xas_for_each for first entry) loads a
> large entry with index point at mid of the entry. So we may miss to writeback
> some dirty page and lost user data.

How do we lose user data?  The inode will still contain dirty pages.
We might skip some pages we should not have skipped, but they'll be
caught by a subsequent pass, no?