Re: [syzbot] [mm?] kernel BUG in collapse_scan_file

Mark Brown
2026-03-19T12:17:12Z

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On Thu, Mar 19, 2026 at 11:56:21AM +0100, Vlastimil Babka wrote:
> On 3/19/26 09:05, Lance Yang wrote:

> > IIUC, this is a dup of the earlier report[1], which I looked into back
> > in January. The root cause is the same: collapse_file() calls
> > xas_lock_irq() without resetting the xas state first, tripping the
> > XAS_INVALID() assertion:
> >
> > #define xas_lock_irq(xas) xa_lock_irq(XAS_INVALID(xas)->xa)
> >
> > static inline struct xa_state *XAS_INVALID(struct xa_state *xas)
> > {
> > XA_NODE_BUG_ON(xas->xa_node, xas_valid(xas));
> > return xas;
> > }

...

> > I posted a HACK fix at the time[2], but David pointed out that Willy
> > had mentioned it likely needs more thought[3].

...

> That "needs more thought" was Jan 5. After 2.5 months later this is still
> messing up linux-next testing due to a known unfixed problem. Completely
> unnaceptable. Willy, you need to drop the new bug check until the known
> problem is fixed.

> Mark, please drop https://git.infradead.org/users/willy/xarray.git from
> linux-next until it stops breaking linux-next. Thanks.

I just saw this mail, I already started running the merge beforehand and
don't 100% trust the scripts not to fall over if I make a change at this
point - I can drop from tomorrow if things aren't sorted by then. I see
the xarray tree hasn't been updated since before Christmas.

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