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Date: Mon, 2 Sep 2024 21:08:39 +0200
From: Christian Brauner <brauner@kernel.org>
To: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>
Cc: Matthew Wilcox <willy@infradead.org>, sfr@canb.auug.org.au, 
	akpm@linux-foundation.org, linux-next@vger.kernel.org, mcgrof@kernel.org, ziy@nvidia.com, 
	da.gomez@samsung.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, 
	Pankaj Raghav <p.raghav@samsung.com>, Sven Schnelle <svens@linux.ibm.com>
Subject: Re: [PATCH] mm: don't convert the page to folio before splitting in
 split_huge_page()
Message-ID: <20240902-leiblich-aufsehen-841e42a5a09d@brauner>
References: <20240902124931.506061-2-kernel@pankajraghav.com>
 <ZtXFBTgLz3YFHk9T@casper.infradead.org>
 <20240902-wovor-knurren-01ba56e0460e@brauner>
 <20240902144841.gfk4bakvtz6bxdqx@quentin>
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In-Reply-To: <20240902144841.gfk4bakvtz6bxdqx@quentin>

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.