From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 4368E352F96; Tue, 16 Dec 2025 15:12:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765897926; cv=none; b=OAB1X+GLxN18MvUN9kYssMxynnz5uhJ5402+c1xLfRfoecOhT0gOlqLmp5PQ56+RXi3JnKfwijogEidOaM2MQWXoSiEmo755KXFk7cLLU9PW+QatkdcDA70XAbkh+jm+x67MsdDtY9x94b7lLVkwLfFBaD+zywEVuIlbpL6Y8Oc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765897926; c=relaxed/simple; bh=sORyT94VtnbOCzIRMMMSdubqBYiWNGJgEe2qZPVcIkA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HW+3nAY9rRkd8KbbQ0ogrOMPCoDkXg0kuWNWTLgwTPTM7jSnGeJnaRRkGni8pcz7HQLV6ct2NPTzJSDnhLgFbyJG3D3hB2eZq9/fhzxHWKS4PZlIUFvIJWXdbGnWpalvRJL6fP05M55Lxg5EftrSGtG88+MLwB/sSzni7pz5DHI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7F93D1516; Tue, 16 Dec 2025 07:11:56 -0800 (PST) Received: from [10.44.160.64] (e126510-lin.lund.arm.com [10.44.160.64]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A6DDC3F73B; Tue, 16 Dec 2025 07:12:01 -0800 (PST) Message-ID: Date: Tue, 16 Dec 2025 16:11:58 +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 , linux-mm@kvack.org, linux-kselftest@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , 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: Kevin Brodsky Content-Language: en-GB In-Reply-To: <37210500-6f6e-46ac-ac2f-ac996308590d@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 16/12/2025 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? It would, thanks! I wanted to use READ_ONCE() from tools/include/linux/compiler.h but for some reason we don't add tools/include to the include path in the mm kselftests Makefile and I didn't want to dive into that rabbit hole. - Kevin