From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B29D312B94 for ; Thu, 19 Mar 2026 11:07:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773918436; cv=none; b=HoUK24RPtUz24eIOHrOMC1ITyk9q4eQDm7YBQL+QccrmfKO0LUaXf9K6BGkpxZLy6wlOQ0h2LJm30DnveUyhNbhnbi1WbAwOxcshAjkXHgI0dBetRxO+M9E7I2ec3dbO8Ai26pxv95ugpYnpTV8H8fyayHUyhogauZvRa4n7qlk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773918436; c=relaxed/simple; bh=CV8omsFptplFHRG3329dbSm62IiQAOIJxztrZtHZO5o=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=h13JaUZgAl4sfY6PCylfm+hGLp9eFwOYOskyiHaRgkdlebTZZeBnM1841gYkiQ6CT8q/7nYzHXbSv/axUXKoyK0RSFbQvE/bZYevkVDbYB6BRxmCL5dbFZ495w8zkgjwK+Xy3hb5Kk74weR97353BWBHgNi3TLD9QLPy/+98U9I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MPr0tZlk; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MPr0tZlk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 35C57C2BC87; Thu, 19 Mar 2026 11:07:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773918436; bh=CV8omsFptplFHRG3329dbSm62IiQAOIJxztrZtHZO5o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MPr0tZlkqWEPEvseOW19Cg60NMjtp5kP17U5edVqBT+fTmuI4OT9X3sZ8TO42ap2b 6CR7VPouXluz3LXDcc84dLK1ScsyMw4tMTlngLzanfoxEHerVqCv9kRIaJ4dMDQbd4 A/CtZ1rDJTUHrLP32GcvrH7pMt5eNL8pmUycePYgbkXzzd3q+qt49zIm7QO9I3VLUk ZtQ3x57fpGuBvHN2JKnSHmCn2scyCrAwJberaF0ywbMH3Nsm+NIeJeKsm+jsD5mQgM FBxHxRT1Ck5b2DuxfRH0BUwK3jc7mVY2aIJ3/pg5Di0hunuSqfrVPh6eY3oECH61Zg POFPtTqGJJ+Sw== Date: Thu, 19 Mar 2026 11:07:10 +0000 From: "Lorenzo Stoakes (Oracle)" To: "David Hildenbrand (Arm)" Cc: Lance Yang , syzbot , willy@infradead.org, baolin.wang@linux.alibaba.com, npache@redhat.com, linux-mm@kvack.org, baohua@kernel.org, ryan.roberts@arm.com, syzkaller-bugs@googlegroups.com, dev.jain@arm.com, ziy@nvidia.com, linux-kernel@vger.kernel.org, Liam.Howlett@oracle.com, akpm@linux-foundation.org Subject: Re: [syzbot] [mm?] kernel BUG in collapse_scan_file Message-ID: References: <69bba3c0.050a0220.227207.002b.GAE@google.com> <10e5f1d6-077d-4783-aa16-6c8b98cb9e74@lucifer.local> <8ab10631-4672-4196-b32e-7c5a01707424@kernel.org> <37b48d94-9576-4529-8576-d4ed615d4768@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <37b48d94-9576-4529-8576-d4ed615d4768@kernel.org> On Thu, Mar 19, 2026 at 11:59:57AM +0100, David Hildenbrand (Arm) wrote: > > We shouldn't, really, be just ignoring splatting kernels like that. At least > > that's my personal point of view on it. > > Yes, we shouldn't. > > > > > But anyway I really don't have the time or energy to try to track this down or > > push on this further. > > The problem I'm having is that reverting the commit might hide a real > problem, and understanding weather there is a real problem requires ... > real work. > > Willy said > > "It *might* still be safe in this instance; I'll look > at this carefully for a bit and decide how best to fix it." > > That likely didn't happen. Yep, and in that case given the assert is suspect, the correct thing is to drop the introduction of the potentially-buggy asserting logic rather than tear our hair out as to whether there is something real or not. > > Later he said: > > "But this is a long and complicated function (over 400 lines!) and I > don't know if fixing this one way or the other would serve to make other > bugs more likely or expose some future problem to the debugging code." > > with > > "This isn't the kind of thing where you can just jump in with a one line > patch and actually be helpful, sorry." Yup, so again really I don't think the kernel should take the xarray debug patch until it is discussed and verified as correct on-list. See the discussion with Vlastimil. > > So I am clueless if there is a real problem there or whether it's just a > false positive. And whether (if it's a real problem) the simple fix > would actually be a good temporary fix ("make other bugs more likely"). > > I can try finding some time to look into that, but pagecache code is not > particularly the code I'm familiar with ... I don't think we should waste our time on it, willy's series should be yoinked until it can prove itself for-sure well behaved. > > -- > Cheers, > > David Thanks, Lorenzo