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[23.116.43.216]) by smtp.gmail.com with ESMTPSA id 00721157ae682-8848608617fsm2387337b3.9.2026.09.10.10.16.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Sep 2026 10:16:31 -0700 (PDT) From: Ravi Jonnalagadda To: sj@kernel.org, akinobu.mita@gmail.com, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Cc: akpm@linux-foundation.org, corbet@lwn.net, bijan311@gmail.com, ajayjoshi@micron.com, honggyu.kim@sk.com, yunjeong.mun@sk.com, ravis.opensrc@gmail.com, rientjes@google.com, weixugc@google.com, jic23@kernel.org, gourry@gourry.net Subject: [RFC PATCH v2 2/9] mm/damon/core: read the CPU number with preemption disabled Date: Thu, 10 Sep 2026 10:16:16 -0700 Message-ID: <20260910171623.6638-3-ravis.opensrc@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260910171623.6638-1-ravis.opensrc@gmail.com> References: <20260910171623.6638-1-ravis.opensrc@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 390D21C0003 X-Stat-Signature: artzghan46m9uufgzsapknybymh1zbqd X-Rspam-User: X-HE-Tag: 1789060593-386057 X-HE-Meta: U2FsdGVkX18cVMKqxE6JEDs3msmlWqZ0eH8bCg7fZaytkcYB5jAKFrxjwC8bxpPcmoGbjpDJlgrZ4IDV+LBv5wj7SmG3RIYLJKTj9KhBPrxR2i+v9++xfdeLvSPkIrrpxqe9o/8pK1l0GxvRi+yj6i84Y4WMEsRbij1kx/Ny2yqjutqnkLwdvprK+i88/baXIkkKUB9L3wiIGtAhiynEhXa93MzmmSgClYXzoVajlGc2MGUe9ggi9BPfUiVajm2DthV0G1K35WlCR88BG7uEbQDKvWP6v4EvKiTDOB4WXDHfWdWckS5xhkAFePtwlAJ6byTdOXUIbsZWGv94Ffubd7f1byP4y/UqH4X3xYFVovqTDd6QIu460XiRz1dAUoPjeBjKMPd/Bd5R1G2+XvY3EtWvnkt2ayC5H/4b0f/inHxrfDlVCuNVLG1JVM5VPWjUh8mm8ODi69bS8uuJBtmSSauNJVQegWuTOYwoxv655BDEtRV55ZXIAOV5ySS9DV3FFUL5CLs1RYdrre22LctN7ANR9oE9CNGM0K7jSBaWUskotuN7jCqVuDZ29DjDG4R2l16aEYfzIsOppiF8sr6QVm59IQnV/buTXuJdTt98FWUjus2diQZORZ1fB3/0ElA/Zl+bl4yBOndUS23BkVrmIX6d1B0W3RPVKfQYs13LnxFrPewU1lsDyVetx0+rBxhNjP6uN8D7smgGnv8KLi6VW9e7E0C6Yn4Z8RA1fOVmi1a0//rAA5ViJNZKNvW0QwETvOtrSKLCHlqMXHK9m6uF1e3Oijg0ztDqD7aF9rPG12CrvoxV9mY9gw0NkuW6HZH+MTPWYUMOYQ3SUOiKacpomsfs9WPsWFwFiO1SUjFrpsrq7QBD2T0LgzX8CxNL5SUtKJta9hwqhTZCg12eiZxt9sfxf6Q9Y/IH2WVU0bNOmOvJCngnmmh1iImAWS6CRDWeQoEAL0yB9iwlsJ4n2V2 szqyL089 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: damon_report_page_fault() runs in fault context, which is preemptible, so reading the CPU number there triggers a "using smp_processor_id() in preemptible" report. Read it with preemption disabled, and keep it disabled across the report so the recorded CPU stays consistent with the per-CPU ring the report is queued to, which is selected the same way. Signed-off-by: Ravi Jonnalagadda --- mm/damon/core.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 5fdb5922edb78..991ddb9a09414 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2514,7 +2514,6 @@ void damon_report_page_fault(struct vm_fault *vmf, bool huge_pmd) struct damon_access_report access_report = { .vaddr = vmf->address, .size = 1, /* todo: set appripriately */ - .cpu = smp_processor_id(), .tid = task_pid_vnr(current), .is_write = vmf->flags & FAULT_FLAG_WRITE, }; @@ -2524,7 +2523,15 @@ void damon_report_page_fault(struct vm_fault *vmf, bool huge_pmd) else access_report.paddr = PFN_PHYS(pte_pfn(vmf->orig_pte)); + /* + * This runs in fault context, which is preemptible, so the CPU number + * is read with preemption disabled. Holding it across the report also + * keeps the recorded CPU consistent with the per-CPU ring the report is + * queued to, which damon_report_access() selects the same way. + */ + access_report.cpu = get_cpu(); damon_report_access(&access_report); + put_cpu(); } #endif -- 2.43.0