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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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <37b48d94-9576-4529-8576-d4ed615d4768@kernel.org> X-Rspam-User: X-Rspamd-Queue-Id: 8FF6D140012 X-Rspamd-Server: rspam08 X-Stat-Signature: tzwm3p4ayy54cezfcrea5pipk3rgkk1f X-HE-Tag: 1773918437-618142 X-HE-Meta: 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 qmq6gc6e iWelsJP8BvXXajcCqC9ulVX614AQOiGZWrc4Pwp9H3rh3kFeR8iTc4DYSmhOT32F+kFDmy79AB1H5AuSa3a2Xw9Nt3vDNW2MPJW+xCA7Jv7w6XYIhG/raX99ROiNplqMv/IMvF6VPT2Ui0Rc4fyBinHgaxEx55jJUN+kyphVSGW0ArBnSPltMTded2w9mEZjoR0H5PSkjesVGW9E0GsAmxoS1xgJzSgfW4To7mj2tyC7rXr2wDFzeNf83gpQHO+lQt6PAUfxxxkOiCeQY64wRtVONDv66xRyuBpMcGMlVnQQ0OWb82I201DXFDfsmbGX0v2QBWAc4HIoqq4X1yvOfct8yU1DzVtV8YGCXlFlqRaeQs1kmNPses2QgtWIBfWEqHBOMa8w2INL7nPgxlsL7cYZ4QBcEtAoRK3gqsIFgiMpmz4g= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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