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[195.250.132.146]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-3b61ca486edsm10026693f8f.56.2025.07.21.02.51.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Jul 2025 02:51:42 -0700 (PDT) Date: Mon, 21 Jul 2025 11:51:41 +0200 From: Michal Hocko To: David Hildenbrand Cc: Jinjiang Tu , akpm@linux-foundation.org, catalin.marinas@arm.com, lorenzo.stoakes@oracle.com, thiago.bauermann@linaro.org, superman.xpt@gmail.com, christophe.leroy@csgroup.eu, brahmajit.xyz@gmail.com, andrii@kernel.org, avagin@gmail.com, baolin.wang@linux.alibaba.com, ryan.roberts@arm.com, hughd@google.com, rientjes@google.com, joern@logfs.org, linux-mm@kvack.org, wangkefeng.wang@huawei.com Subject: Re: [PATCH] smaps: fix BUG_ON in smaps_hugetlb_range Message-ID: References: <20250721081444.277183-1-tujinjiang@huawei.com> <46a22e7c-51f0-4fd0-8583-447c5e366029@redhat.com> <6f16f99d-2f60-4e0d-a5c7-2dfdeb08bedd@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6f16f99d-2f60-4e0d-a5c7-2dfdeb08bedd@redhat.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: DBE4F180002 X-Stat-Signature: d7ia1nfhbgfsfgwsxunbm79y8mgbsuya X-Rspam-User: X-HE-Tag: 1753091503-977489 X-HE-Meta: U2FsdGVkX19Xkoist0JxNjkSn9BVxDAR+Yg6AHoP9/GFYSPxWMbbK01krMciW21GcAxzD6NRkQV10Z+bMKwYbWxKELZcpOD6L8MC/fPElUB2HmGq191jWVY0tOiPssXizLe3ZvPw3Sx0/+psZRvZ5Zj+t5RAKD8DuWaP2KjdknRh86S85uAO4gC3eJmEx955WD7MENVcgycTr2drXv4JcAK8jZ1xb01u6UhQEBq+nPe+h8h7vn7i8lUHpSfvEeAXk5rwpkVXYhFT4UyMbGR1+WvdwCySd/rKwCpQ5nfvaG7hcqgyl6x+ImAQAZE+UlZ2trsis9jeK+CdRB14CgS6r5HjcdNTOxDAYzkWk5M6xpz8Xa2Oj0Fs4yAhgRHTtf4E2q8s2V7EXxRbM8tUxueeEApMy33U3AuNSQnpquEe680ALZW8aDns93biDnwcMo29zGcxedQWDeY95gNa04KDhs9st4iC2BeQAc+kcihBpi4+DJIHLAu9SFuDJtbx+4Iv7hWbXFPPaD139HhaOWgWQo6ab1LOjAnMkRtpE0H/N04TCbHBZ9fWfj4Ww7OnIiJIjwU4XT/0KbwyFBaZ1BY4NnSh4lsXTM6EDPyBSsgnxctjKR5Y/xkPxSeLOlvUquU8CY1oShyf0WAB7hPOh3rp6i4TKUIm7MTXmE1Nwkiiwn++N21qxe5vFbWvLPhEBb5V1iZ3q/y288ux1akTZrXXqVtuDHGz7/Dvlv1VypSYVHGW1GWLndlKqgzsIDIvCFSvIF3B9K903om/loYe25ojn1MxS7dDave8u6QEVqtG1IhPwniiFc5a6u4jhvGMKOxILrERmURX/lvh7+Y0smSeG+Fq+pijjLz77lpTpHmfBkfQ6V8RL7XhxVmLnBFUPuOarhfeY8fLyKJjZmKR0/kOaRx58bQ14WNzJ2ry5mSjD6HVmIHzAYT4kLYIOWsMJ/IqGHcBa4mQhoyBbk4jLeF Vr0BspkL 0yKe4GP7doppAPBE2/kdruVNokk7D5L0vZROon8228uOlncFCSrMeXRGyiVM7WzouxJh2/DH2G2v8Faqg6MuRjQx3X84UKVEXlcLqF0X0c8SG7vAnBQfXEEdLfsVEExFEv+CB/pRwxs2L3oo= 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 Mon 21-07-25 11:41:18, David Hildenbrand wrote: > On 21.07.25 11:35, Michal Hocko wrote: > > On Mon 21-07-25 11:29:52, David Hildenbrand wrote: [...] > > > Heh, I stumbled over that code many times and wondered "why don't we need > > > the PTL here -- I'm sure it's fine because otherwise we would be getting > > > reports.". > > > > > > In pagewalk code we only hold the vma lock -- see walk_hugetlb_range(). > > > > > > So I think we should just grab the PTL in all these walkers. > > > > I believe the reason that we try to avoid taking the lock in these paths > > is that they are userspace accessible and we do not want to expose them > > to users. I think it would be good to try to rework the code to not > > require the lock even if we get imprecise numbers. We cannot trigger any > > oops of course and that is a clear bug here. Can we achieve the fix > > without taking the lock? > > We grab PTLs whenever we walk page tables, except in hugetlb. So I much > rather want that changed? OK, fair enough. If hugetlb is the only one odd here and we are already living with the ptl already exposed then let's go with a lock here as well. -- Michal Hocko SUSE Labs