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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1778320061; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=h+2pbbVhcPs+O/UiB7Rv0YgrC1Aa3k1+qfWtc56gjcQ=; b=Bv+/YluIxCYzSWDM6r6xXnJk3cZ60VwXTBhEg+4vuryOYu/VZDOfcWSHl1NSKzTOcVVZU8 N9ONn4g9u+bODF/pZpn25LdsBJtLjb3Ou92xRIuM1uxUmaFFksXUmB6YQrRN19fXWWwItv lIQKSwkasHds8/Mds4ZEe9zq3Hvn3fM= From: Lance Yang To: chenwandun1@gmail.com Cc: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, shuah@kernel.org, zokeefe@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Lance Yang Subject: Re: [PATCH 0/2] mm/khugepaged: fix sub-PMD MADV_COLLAPSE range handling Date: Sat, 9 May 2026 17:47:32 +0800 Message-Id: <20260509094732.83643-1-lance.yang@linux.dev> In-Reply-To: <20260507070558.3064142-1-chenwandun@lixiang.com> References: <20260507070558.3064142-1-chenwandun@lixiang.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 47724A0007 X-Rspam-User: X-Stat-Signature: yjcp5ax65een6xzsiz7a9e6k78uftbud X-HE-Tag: 1778320063-313082 X-HE-Meta: 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 RD8dThdn QIpTrEiaxEt23UQA99bChOV1fXyb0D6KgOWXMgZrNuySOkYklcEe2JCIiYUmPp4oj9fGRz10VLwl8wKCHZ1nKIyXo2nfstc0CAAhsIXGuv/VHKt9kZ6GtWUD95Q3FqaP14R8lvpxi5HbK5yVVggYDqZxodSLPeTEDicKrVF6zCSuPPZ2NS/gVyA5VfxHdNcnRTN8Y6jy5z/DVIckW1oFqdB6XH7PDMCwt+exz/ugbfadcnj0tKmpwYV13P1qqWhljAw+V Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, scripts/get_maintainer.pl is your friend :) Please use it to Cc the relevant maintainers and reviewers next time. Cheers, Lance On Thu, May 07, 2026 at 03:05:56PM +0800, Chen Wandun wrote: >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 > >