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b=NAT4xJHqv/vfaFe9m1w9iNPwcaMKlEUIvqtLY6RvG6MVhwXPAJ1XmQih2fV21NpUt MEbuKTBqvw7PsgiKE/xDXbwvU6oPvjiqbinaI4TbkDbrwej1DFCskK3BX2i3W1GBPz cEmNLNXk+N7Jkmi6vszHvmu70jFH5T2Dcw7SpjbRI7MueIyrTrTZo+q3itraQhEN/Q f3p6+voUWojJsA7wdMAmuycCxX16UCJUAHSI5DISp+SCwgyHQ2mfhg0yYnUWFbG/+w 32ASHFNn0kzmmXTE/1Sb/C2pqUla5slcBEfnZ4CyGSUhALQS/+g+9z4FE+ByS39weW m685xUvxDOnxg== Date: Mon, 20 Jul 2026 15:16:29 -0700 From: Dennis Zhou To: Zi Yan Cc: Tejun Heo , Christoph Lameter , Andrew Morton , Christoph Lameter , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sashiko Subject: Re: [PATCH] mm/percpu-km: fix bitmap overflow and accounting in pcpu_create_chunk() Message-ID: References: <20260709-fix-pcpu_create_chunk-in-percpu-km-v1-1-1f64745a84cc@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 6A62E40002 X-Rspam-User: X-Stat-Signature: rdt4rm6e837e1ceahwx59gfj3hfk9qc7 X-Rspamd-Server: rspam04 X-HE-Tag: 1784585794-560460 X-HE-Meta: U2FsdGVkX1+5qmt0+6hc3KmXjdFS48kSWBkQ3MGzHnXyIiw1PIZFGmgXvV/vEyZVxm2ru/IwqrMdcVGOqReXb/h10GHMp/QqnzhbAzoCY+qyum8qq9zPcI7LZdTE4LPwA17uoMb1Y95OqxtMzkS1df30cK8R19OoXwg/VPh7GVYDhsnjeUWtwktc549zM+sKvRUgPKMwKJwQo3eE/vgQDU6RFq8gzAgtuzbssSIOvsmSYbX1vWV2NyLnXIeZLr3FZPHXGYSCynZKafI0iSk/WCxts3+eL8Z7Z7mm2YPqVPAwgvXHkVc7KcBdOx71ppBua0Dy+N269/I2xc7zKuoX5FpyYYgU+fAogwaOvt3qdIxC4VD2my67egRbaK+sn3muDcgpLOisX2vZkJWxcJrUblV8qlvi7sQesRUVkih2fwM6ZjiktrxewiSZeojtCAbqkoNLTYDjyJQXN6rRwqpP701QOfC9IRfi8kJS+f7WxDIFsVAlOC28I+GfeTx/aoq6bGZCFXSdzp42T1qZ1S+nE+t1lAFfuHb7oAg+mhH/FEwrAcorUcAL8SYDKEItRzRqSfhWZ1lnJ2SyZiBIqNbUmB0k/JSTCrRGNFdzNyxyu/Hrjxv10heU8AfG6gCHvSqeTyDJD4pTksFBV8Yd0oEdK0y0m8E0PkE6v6iCeets7WelqH9InCs4uLGqERSiCuBzW4sQXJQ7b9oM3jyKqAQvLc7JgTk+WK/o1XPacbVvkIIE3SA35pPcAJXDj1yVDKz+gsPu8Z16kgetNCQrnkXzsVch6VWcmG3bQqYls7g1NHXjwTXl+6XR8zydXjI4ffWiRr28TV1UAdKZ/bFjAaiB6sQFxfaY4Vlq2WkPXXNHaz6ikzficwr8JvO/MhkiyzkUB4SHqd8k+Sd0PxQjGP8jcFl3Wm0sRLxJBgh2iO5RQGd+9T2XiHODoFCU6dFbolzbiJwrM3X6hlJD6JUqSPe 2sDKy6DL XIvadMfWa5krW1TMzJRLVxFbDS90nNZiNG9QBv1/cqVg4e6aN37PVbqN5Z9Mh/H3T9RcSs79PbR3e63MO03d2y3O+ZCe9GuTOf84Nn8iTBO98xvlgnY7miGjPWsgId620QJZ5VJ+eui40+WxfYYrydLq9KEHkrpft02MOUFE0dBrHevJAm98G+h4jDIlwnmd68nQJPlYVSfyIPCAivbZZFcfi/QJimHsXcojb/qXMSJGOR6byEGt/53U91eCipf772HEy2TL6ZSrgjYqIKmtrbetzfQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Zi, On Mon, Jul 20, 2026 at 03:20:31PM -0400, Zi Yan wrote: > On Thu Jul 9, 2026 at 3:12 PM EDT, Zi Yan wrote: > > In pcpu_create_chunk(), nr_pages is the total contiguous backing > > allocation, i.e., nr_units * pcpu_unit_pages, but pcpu_chunk_populated() > > uses it to set chunk->populated, whose size is pcpu_unit_pages, bitmap. > > Since bit N in chunk->populated means page offset N inside every unit is > > backed. When nr_units > 1, the function writes beyond chunk->populated. Fix > > it by using chunk->nr_pages. > > > > It also fixes the global pcpu_nr_empty_pop_pages accounting, since > > pcpu_balance_free() only iterates up to chunk->nr_pages. > > > > Commit a63d4ac4ab609 ("percpu: make percpu-km set chunk->populated bitmap > > properly") introduced the bitmap overflow issue. Later, > > commit b539b87fed37f ("percpu: implmeent pcpu_nr_empty_pop_pages and > > chunk->nr_populated") added pcpu_nr_empty_pop_pages and caused the > > accounting issue. > > A gentle ping on this patch. It would be great to get some feedback. > Thanks. > Sorry, this is right and I missed it years ago. Acked-by: Dennis Zhou Thanks, Dennis