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Thu, 07 May 2026 00:06:06 -0700 (PDT) Received: from intel.company.local ([210.184.73.204]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c825379099bsm1200164a12.14.2026.05.07.00.06.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 May 2026 00:06:05 -0700 (PDT) From: Chen Wandun X-Google-Original-From: Chen Wandun To: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, shuah@kernel.org, zokeefe@google.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: [PATCH 0/2] mm/khugepaged: fix sub-PMD MADV_COLLAPSE range handling Date: Thu, 7 May 2026 15:05:56 +0800 Message-ID: <20260507070558.3064142-1-chenwandun@lixiang.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit madvise_collapse() computes a THP-aligned window from the caller's range: hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK /* round up */ hend = end & HPAGE_PMD_MASK /* round down */ When the caller's range is smaller than one PMD (2 MiB) and/or not PMD-aligned, hstart can end up greater than hend. In that case the collapsing loop is correctly skipped, but the return value was computed as ((hend - hstart) >> HPAGE_PMD_SHIFT): with hstart > hend the subtraction wraps unsigned, producing a huge value, the comparison "thps != 0" fires, and -EINVAL is returned instead of 0. A concrete example: /* both cover less than one THP; both should return 0 */ madvise(aligned, PAGE_SIZE, MADV_COLLAPSE); /* OK, returns 0 */ madvise(aligned + PAGE_SIZE, PAGE_SIZE, MADV_COLLAPSE); /* returns -EINVAL */ The fix moves the hstart/hend calculation before kmalloc_obj() and returns 0 early when hstart >= hend. This also avoids the kmalloc, mmgrab(), and lru_add_drain_all() calls for ranges that trivially contain no PMD window. The same effect could be achieved by only guarding the final return expression, but early-return keeps the no-op path free of the allocator and drain overhead. Patch 1 fixes the kernel bug. Patch 2 adds a selftest with two cases covering the hstart == hend (aligned, was already correct) and hstart > hend (unaligned, was broken) scenarios. Chen Wandun (2): mm/khugepaged: fix spurious -EINVAL from sub-PMD MADV_COLLAPSE range selftests/mm: add MADV_COLLAPSE sub-PMD range tests mm/khugepaged.c | 9 +- tools/testing/selftests/mm/.gitignore | 1 + tools/testing/selftests/mm/Makefile | 2 + .../selftests/mm/ksft_madv_collapse.sh | 4 + .../selftests/mm/madv_collapse_range.c | 141 ++++++++++++++++++ tools/testing/selftests/mm/run_vmtests.sh | 5 + 6 files changed, 159 insertions(+), 3 deletions(-) create mode 100755 tools/testing/selftests/mm/ksft_madv_collapse.sh create mode 100644 tools/testing/selftests/mm/madv_collapse_range.c -- 2.43.0