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Wed, 10 Sep 2025 08:57:16 +0000 (GMT) Date: Wed, 10 Sep 2025 10:57:15 +0200 From: Claudio Imbrenda To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Jason Gunthorpe , John Hubbard , Peter Xu , Christian Borntraeger Subject: Re: [PATCH v1] mm/gup: fix handling of errors from arch_make_folio_accessible() in follow_page_pte() Message-ID: <20250910105715.7f4f8495@p-imbrenda> In-Reply-To: <1228a0a7-660e-4993-887d-66bc2c37b8f4@redhat.com> References: <20250908094517.303409-1-david@redhat.com> <20250909180757.1114d727@p-imbrenda> <1228a0a7-660e-4993-887d-66bc2c37b8f4@redhat.com> Organization: IBM X-Mailer: Claws Mail 4.3.1 (GTK 3.24.49; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: QRrBKBaZ89nXHwCvmJ9dEt-qtRQn2gBd X-Proofpoint-GUID: QRrBKBaZ89nXHwCvmJ9dEt-qtRQn2gBd X-Authority-Analysis: v=2.4 cv=EYDIQOmC c=1 sm=1 tr=0 ts=68c13d6f cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=kj9zAlcOel0A:10 a=yJojWOMRYYMA:10 a=20KFwNOVAAAA:8 a=nCIUJmz4GBJYDfQ3j3gA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTA2MDAyMCBTYWx0ZWRfX9b9+jsRX4zrI BlQMWMK5YlVzA97p2eodgwolIMp/eLO+pHH+HHJZS2VYUKORt2Ibt2r5yYE22ESNd9VYYFb7FVu M6NGrV9M1/QFyyLXD0NWhT5pjOBZ23FjYyPdm38n3dRL3kBXTVAudv64vdHWj3oRnksHzKOMo8S uz9H8dzH++wQVXvMZIhZjPfwdlaPS5pVFqKHpvj2xRQXwPiQEHcIjkBWU7fROQ9CxtAP386FQwW uzXDD8uCqL+PkiySP9tURCz/+cskJ8HKyPmB1bIPsYgnIgZCD6l+OLi2F/5IiFAz2oSafHbgTpI PEpIZLQcom1SQlttAtnQBIEEpErwvTxrpBTHSxmJxqsH52PwXW6XUhsP1qcj9xKWUGlF47VqWuJ eq6TWflf X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-09-09_03,2025-09-10_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 adultscore=0 suspectscore=0 spamscore=0 impostorscore=0 priorityscore=1501 phishscore=0 clxscore=1015 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2509060020 X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 453DB100002 X-Stat-Signature: wybfaguoymyep8mymooahscqapbu8bgo X-Rspam-User: X-HE-Tag: 1757494641-650617 X-HE-Meta: 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 nvaWyW4v uOTle+cwfp+BbOH4BZlJ5Gkjgpd8Is9+KMaL6hgD0T5ZqrS56IUJLb43g7YVrgZIRDp6m3rWvksEk+iqTK4BuuY03DsozQwUhpwtaTnWkn5zm/gBKl6Dnz8GhtMSohDLRKx8MajS+/Kr67ruac3uCrN4S6FOGjb1sdYZ+/uLTKh8FeRXnO+EPB07vOC95erDhslZUm562sRwOse4NxlZ0dWK0UKqxv1cYrvFvc08HFWqHlQ8qqBsfiGWx0RcG6Igo7Nbvl5xXTan/kX23s8i9tQgaIBQA6W3B/1Z8jDQicQxITvh1X/rdP0Q6usSLRpivM7PXBylwJlxhxxTFhWbbEF3u5gCei8EFkhd/ykuqg0ha8C3ACUwB52JdvgAPTT3834XAbmXfGI0G8aS6UoGANGQkdO/eS/GZOQLf X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 9 Sep 2025 18:15:17 +0200 David Hildenbrand wrote: > On 09.09.25 18:07, Claudio Imbrenda wrote: > > On Mon, 8 Sep 2025 11:45:17 +0200 > > David Hildenbrand wrote: > > > >> In case we call arch_make_folio_accessible() and it fails, we would > >> incorrectly return a value that is "!= 0" to the caller, indicating that > >> we pinned all requested pages and that the caller can keep going. > >> > >> follow_page_pte() is not supposed to return error values, but instead > >> "0" on failure and "1" on success -- we'll clean that up separately. > >> > >> In case we return "!= 0", the caller will just keep going pinning > >> more pages. If we happen to pin a page afterwards, we're in trouble, > >> because we essentially skipped some pages in the requested range. > >> > >> Staring at the arch_make_folio_accessible() implementation on s390x, I > >> assume it should actually never really fail unless something unexpected > >> happens (BUG?). So let's not CC stable and just fix common code to do > >> the right thing. > >> > >> Clean up the code a bit now that there is no reason to store the > >> return value of arch_make_folio_accessible(). > >> > >> Fixes: f28d43636d6f ("mm/gup/writeback: add callbacks for inaccessible pages") > > > > Ooops! > > > > thanks for finding and fixing this > > Thanks! Is my assumption correct that this is not stable material? > your assessment looks correct, an error return value can only be caused by a bug