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Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Arnd Bergmann , Greg Kroah-Hartman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lance Yang , syzbot+c181d3198e98f8aef8b9@syzkaller.appspotmail.com Subject: Re: [PATCH] drivers/char/mem: mmap readonly MAP_SHARED-/dev/zero correctly Message-Id: <20260928172654.7030810755eefd2a1503a0ee@linux-foundation.org> In-Reply-To: References: <20260924-fix-dev-zero-readonly-shared-v1-1-153c2111e323@kernel.org> <9efc7bc1-8d9d-49ac-b856-003e81558411@kernel.org> <20260924195826.70a87d6fb78d754bc73892cd@linux-foundation.org> <95e91b4a-ca16-49a3-9a1a-5b38afa6f08d@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: oqcutiqqxwyymp7qcqboc1zs69ztciuq X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 9068CA0004 X-HE-Tag: 1790641616-727014 X-HE-Meta: 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 +GPa7fw3 h3IfKDo0O2EDh5v9Sp5yFTy+6a9DYDneNNe9XcunrMOY826pj+MWyH36kMbiHcP8JQhsrbWHBSeEcL5JThEbp6HlPzcijV1/1yorFG2z4UoX4Thxzbadro9jihrq3Dsq8hKI2/xMD4ZKYajXyG3FKJTOVXXoKY6qNnHBBYRTmaTgrayWzS0B43exPE5g1pKCQ7uAzZzq2qA3EXL8f440p3ojpZTCrJrYcCohbLoOeLKh3uzskMxJKHkKGA/bLl/9+meP57SDWWes9Qg/972rKOnMbPqe09fj/a+qnnoKdk8H+iPEwIjhWhDwryF6efNAz2QGkzGwZy+2rg3ofjCHGtCdNJALwN8ES7M86ZLJ2D+AQ9h/poG4e0Q/waOcewpnhJzll2/tIN9A+a5r3LxnNu9CMGagaS4zBijgEA3wCPFsaXnAZBB6YEEU0alc3zlckz06U/D4rPthl8gs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 28 Sep 2026 13:59:47 +0200 "David Hildenbrand (Arm)" wrote: > > > > >> > >> b) Do what Lorenzo proposes. This will allocate real memory. Someone decided to > >> use MAP_SHARED, for unknown reasons, so I'd assume it's unlikely that > >> something breaks, but you have a point. > > > > I would say this patch is the right fix for the moment to fix the assert, and we > > can chase up with other approaches afterwards. > > It will get backported, so we better be careful. I don't think it'll get backported. I hope not. The Fixes: target of 93c0c8dc87f6 ("mm/rmap: use anon pgoff to track MAP_PRIVATE file-backed anon folios") is new in v7.3-rc1, so this will go in as a hotfix against this -rc cycle only.