[RFC PATCH v2 2/9] mm/damon/core: read the CPU number with preemption disabled
From: Ravi Jonnalagadda <hidden>
Date: 2026-09-10 17:16:36
Also in:
damon, linux-mm, lkml
Subsystem:
damon, memory management, the rest · Maintainers:
SJ Park, Andrew Morton, Linus Torvalds
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 <redacted> --- 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