Re: [PATCH v2 1/2] mm/memory: recheck PG_uptodate after ->page_mkwrite()

[Kiryl Shutsemau]

On Mon, Nov 09, 2026 at 08:30:47PM +0000, Matthew Wilcox wrote:
> On Mon, Nov 09, 2026 at 12:04:01PM +0000, Kiryl Shutsemau (Meta) wrote:
> > do_shared_fault() unlocks the folio around ->page_mkwrite(). Writeback
> > can lock it in that window, fail, and clear PG_uptodate with the folio
> > left in the page cache. ecryptfs_writepages() does this when encryption
> > fails. filemap_page_mkwrite() relocks the folio and checks only
> > ->mapping, so the fault maps a folio that is not uptodate:
> 
> Filesystems that do this are buggy.  They shuld be fixed, not worked
> around like this.

Fair. What is your take on the way out?

Is there a timeline for the filesystem fixes?

Until they land, mm should still not map a folio that is not uptodate.

Would WARN_ON_ONCE() and SIGBUS, like the other checks in 2/2, work for
you? It flags the buggy filesystem instead of hiding it.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov