Re: [PATCH] mm: don't convert the page to folio before splitting in split_huge_page()

[Christian Brauner <brauner@kernel.org>]

On Mon, Sep 02, 2024 at 02:48:41PM GMT, Pankaj Raghav (Samsung) wrote:
> On Mon, Sep 02, 2024 at 04:21:09PM +0200, Christian Brauner wrote:
> > On Mon, Sep 02, 2024 at 03:00:37PM GMT, Matthew Wilcox wrote:
> > > On Mon, Sep 02, 2024 at 02:49:32PM +0200, Pankaj Raghav (Samsung) wrote:
> > > > From: Pankaj Raghav <p.raghav@samsung.com>
> > > > 
> > > > Sven reported that a commit from bs > ps series was breaking the ksm ltp
> > > > test[1].
> > > > 
> > > > split_huge_page() takes precisely a page that is locked, and it also
> > > > expects the folio that contains that page to be locked after that
> > > > huge page has been split. The changes introduced converted the page to
> > > > folio, and passed the head page to be split, which might not be locked,
> > > > resulting in a kernel panic.
> > > > 
> > > > This commit fixes it by always passing the correct page to be split from
> > > > split_huge_page() with the appropriate minimum order for splitting.
> > > 
> > > This should be folded into the patch that is broken, not be a separate
> > > fix commit, otherwise it introduces a bisection hazard which are to be
> > > avoided when possible.
> > 
> > Patch folded into "mm: split a folio in minimum folio order chunks"
> > with the Link to this patch. Please double-check.
> Thanks a lot!
> 
> I still don't see it upstream[1]. Maybe it is yet to be pushed?
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/commit/?h=vfs.blocksize&id=fd031210c9ceb399db1dea001c6a5e98f3b4e2e7

Pushed now.