From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9D37C2459ED; Thu, 18 Dec 2025 08:05:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766045131; cv=none; b=NoLgiuHdpkDmGs91VRdX+x7EdzNnu0jP5t/7Oqjx0zZdc/bWbAlEoE4jNgD5jnJAxuUVXGNT0CTnkqtKwVmwke4KPBJ3kisQKhrnRy3JNm2LXHl/OU/RQItKHlxO8hGchAH0zXStY8DiwG4JUqrBIB3qCYKNi9BET1X1sraC/68= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766045131; c=relaxed/simple; bh=OzSTS8I7zeGFfn+9aQoFwN8O+cmLb6QBvAXAvMo9Ucs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rZQk/x2rwdk0bK0cs6Sgj114zMDm/0fKwDczCllkkzANUoIUCf+3VHhfBctSJgxIOBdV2OfcItOkf+ygfc3FoR22j6dRJFPeTFi/ujUFWQn7D+MHKe5Eny03vmmLQBxQiCYHl8OL6sCAGXRU/n/qcGxYZyUotwUPsiVGF6Gn34M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ly158k2o; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Ly158k2o" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 15EA0C4CEFB; Thu, 18 Dec 2025 08:05:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766045131; bh=OzSTS8I7zeGFfn+9aQoFwN8O+cmLb6QBvAXAvMo9Ucs=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Ly158k2otsUXsxGvg+hMLHK6XdetqPckQe980NBs5BY+zeog2Ysm0rMLTxUR1xmmq Lgyrf96RU2TY79qsWp9dH7QjNC+lyBGTOYaVFGbidHlB0ci74xRtDrO0u43ioFqhVG umLnwu9NFs/nq84gi2yBVjR0ps7YmTwFcXykBRNR/aoFwFr3mdejAucpCJchzNAOOH cpoLvN5RU4E7HrGGT1myxrSe4A++/WmufZPPel1aYw9e1PQAuhyhWfFli3n7hMNXMP KMnhCPxrQsuW7BO1/19blQi8ghAKjBfISLuFefKKWc7R+OoAZGnot2H0pGULjyN9fy IY/gLIGP8D3lg== Message-ID: <6aa47cdb-d2e7-4977-929b-7019b6f991c1@kernel.org> Date: Thu, 18 Dec 2025 09:05:27 +0100 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/4] selftests/mm: fix faulting-in code in pagemap_ioctl test To: Ryan Roberts , Kevin Brodsky , linux-mm@kvack.org, linux-kselftest@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Lorenzo Stoakes , Mark Brown , Shuah Khan , Usama Anjum References: <20251216142633.2401447-1-kevin.brodsky@arm.com> <20251216142633.2401447-4-kevin.brodsky@arm.com> <37210500-6f6e-46ac-ac2f-ac996308590d@arm.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <37210500-6f6e-46ac-ac2f-ac996308590d@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/16/25 15:56, Ryan Roberts wrote: > On 16/12/2025 14:26, Kevin Brodsky wrote: >> One of the pagemap_ioctl tests attempts to fault in pages by >> memcpy()'ing them to an unused buffer. This probably worked >> originally, but since commit 46036188ea1f ("selftests/mm: build with >> -O2") the compiler is free to optimise away that unused buffer and >> the memcpy() with it. As a result there might not be any resident >> page in the mapping and the test may fail. >> >> We don't need to copy all that memory anyway. Just fault in every >> page by forcing the compiler to read the first byte. >> >> Cc: Usama Anjum >> Signed-off-by: Kevin Brodsky >> --- >> tools/testing/selftests/mm/pagemap_ioctl.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/tools/testing/selftests/mm/pagemap_ioctl.c b/tools/testing/selftests/mm/pagemap_ioctl.c >> index 2cb5441f29c7..67a7a3705604 100644 >> --- a/tools/testing/selftests/mm/pagemap_ioctl.c >> +++ b/tools/testing/selftests/mm/pagemap_ioctl.c >> @@ -1056,7 +1056,6 @@ int sanity_tests(void) >> struct page_region *vec; >> char *mem, *fmem; >> struct stat sbuf; >> - char *tmp_buf; >> >> /* 1. wrong operation */ >> mem_size = 10 * page_size; >> @@ -1167,8 +1166,9 @@ int sanity_tests(void) >> if (fmem == MAP_FAILED) >> ksft_exit_fail_msg("error nomem %d %s\n", errno, strerror(errno)); >> >> - tmp_buf = malloc(sbuf.st_size); >> - memcpy(tmp_buf, fmem, sbuf.st_size); >> + /* Fault in every page by reading the first byte */ >> + for (i = 0; i < sbuf.st_size; i += page_size) >> + (void)*(volatile char *)(fmem + i); > > We have FORCE_READ() in vm_util.h for this. Perhaps that would be better? Agreed, and if we have multiple patterns where we want to force_read a bigger area, maybe we should provide a helper for that? -- Cheers David