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[89.103.124.216]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488fc0f82bbsm565012525e9.3.2026.04.20.22.59.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Apr 2026 22:59:10 -0700 (PDT) Message-ID: <836b0ce8-f427-434f-984b-4fc60b02c810@redhat.com> Date: Tue, 21 Apr 2026 07:59:08 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] selftests/bpf: Page out as late a possible in file_reader To: Mykyta Yatsenko , bpf@vger.kernel.org Cc: Andrii Nakryiko , Eduard Zingerman , Alexei Starovoitov , Daniel Borkmann , Martin KaFai Lau , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Jiri Olsa , Shuah Khan , Mykyta Yatsenko , linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260420134637.2513867-1-jmarchan@redhat.com> Content-Language: en-US From: Jerome Marchand Autocrypt: addr=jmarchan@redhat.com; keydata= xsBNBFO1HMkBCAC7ldQoS6JT5Fk9gRCJQrZjexkWsUhK8LVmKJXpbybAnojJOHrD7H02FwDh F6kAZVZMBAFf5aUZQHtjF+UvBNiPptIohb7ODLS/hiTZHpUI1/JkBOZ8wZbWakkTEwsj5Ccw czVB0PCDm+coE5BcQezEEn3ENNO45X2YQ6DeDzdpYRiCEOQufDPAwvSHoP/lXfRayNDuNRxd 20RS73qTYupcbMDEEYd24vvh62gVVusuljUPWaDB7w+z6i7zwzTzkoTGW/OURSnOy731VGsK BniaFdLAipta1rhg43no0qJuAqxLEzgxUYiDN3cZf7Nf6eSnG71ugUUtYgc1d5I1Fe1RABEB AAHNJUplcm9tZSBNYXJjaGFuZCA8am1hcmNoYW5AcmVkaGF0LmNvbT7CwJgEEwEIAEICGyMG CwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAhkBFiEEKhfvHc6w3BYc12CSdPMckK2y6gIFAmgH aZgFCRgUChcACgkQdPMckK2y6gKeUQf6AvMundBabBuvOQIhz/OP4VrUV/ilEAxXqPPEqv8p O+GKSnWBdYpIR/nBh62u/GN88l1LjgTWh1PbhvUtB1TviXtapp/MN9IcPVJkJVFh0KdyObMt 4muJpUrEmnyn9WOZKhfEZGaXBq5zraqBrg4u1r0H0aoXDhSd/EF9JS2Qnm8rWaktzGotgGkJ ntjh5BuZCHd9YSTIYkux5tUO0LFitgiHgE/AIDk+2lKTCEei15SjWNCo3DluagDpfOjgtGSY 6UNRH1XBKH86EKKJelsBCNRalvYQRzmzS/GAYLaHBqyACmKsGmERcLpvmJsQqWF7sMJXy412 mr+b7iufKihOtc7ATQRTtRzJAQgAxpKIAn2SVSfk3CsskkE3FzLfu3suaueUVtS/ZaY/K8hf M3oB1AA/jQFwIwXIeT8rz2kRjDkNkli3DMAMovCuABLCun+Ts8cSqJN22iPVD5AuwkiZPcvm v1VpkFxJE4OwyrpJOIcyPHRXyTYO6V/nTuD64+BUkLPf0dfGKetz9k89qGeacx346JPZndfb 7/rUI9Z7FW9mTTyI3IP6x0eLOFKmzULsV8yrGJqU1xUuLD3bh/fbvljqlqWjvervZKsVNPGM yOjRQeu7T/E0SMNTV2dXUP7jyJhmdKQ0uDrjE7kwVjZtrmb94915Gne2+ou2Vh+NwhOpbCIo eWgSBfxrYQARAQABwsB8BBgBCAAmAhsMFiEEKhfvHc6w3BYc12CSdPMckK2y6gIFAmgHaZgF CRgUChcACgkQdPMckK2y6gJLZQf+O5J+4qMLK3+RpCNP6jrUp9v/67t1CaVyHhbl4XOzR0jR iXHauB7MtIu9AYd8b+KcCZoXjtX34uBhB8XwXZjVTp6aD6ILKZYtcm+KJ7bioXgJSwaarS8W kpDUOKnphOpfCL9c1qLRVGKCwvpAgG+RK/FMT/gq05idrTqaH95CS2WMyDar7IwWU6qzYykA GdumHbxQYMSgSBhmsGfYXa+QAYOI/w6TivVjVyTD8feL9yN0zxACMVKRNy3xeDvPQQm7jP+Y hbgyBmp4HfLY/BS7/FKS5Tv1ke4kBDohXRJEGxjzrTWLUNZBIusgT6lPVX4OjlvwX8cjsxnR nZg+C3oGDA== In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/20/26 6:52 PM, Mykyta Yatsenko wrote: > On 4/20/26 2:46 PM, Jerome Marchand wrote: >> The file_reader/on_open_expect_fault fails consistently on my system. >> It expects a page fault on first dynptr read of some range the exe >> file of the current process because it has paged out that page range >> earlier. However a lot can happen to that range (which depending on >> the actual memory layout could contain text section, data section, >> sections )related to dynamic linking...) between the moment it was >> paged out and the moment the bpf program expected to hit a pagefault >> actually run. >> >> A bit of instrumentation with mincore() shows that pages from that >> range were accessed several times before the program is run. In >> particular the call of file_reader__load() seems to fault all the >> range in. >> >> Move the call to madvise(MADV_PAGEOUT) to just before attaching the >> program to minimize the risk of having those page pulled back in from >> under our feet. >> >> Signed-off-by: Jerome Marchand >> --- > > Thank you for the patch, the change looks good. Does it fail > consistently on 4K page size? It did when I ran the test manually. On our automated testing system, it failed intermittently. Regards, Jerome > > Acked-by: Mykyta Yatsenko > >>   .../selftests/bpf/prog_tests/file_reader.c    | 22 +++++++++---------- >>   1 file changed, 10 insertions(+), 12 deletions(-) >> >> diff --git a/tools/testing/selftests/bpf/prog_tests/file_reader.c b/ >> tools/testing/selftests/bpf/prog_tests/file_reader.c >> index 5cde32b35da44..48aae7ea0e4bb 100644 >> --- a/tools/testing/selftests/bpf/prog_tests/file_reader.c >> +++ b/tools/testing/selftests/bpf/prog_tests/file_reader.c >> @@ -10,6 +10,7 @@ >>   const char *user_ptr = "hello world"; >>   char file_contents[256000]; >> +void *addr; >>   void *get_executable_base_addr(void) >>   { >> @@ -26,8 +27,7 @@ void *get_executable_base_addr(void) >>   static int initialize_file_contents(void) >>   { >>       int fd, page_sz = sysconf(_SC_PAGESIZE); >> -    ssize_t n = 0, cur, off; >> -    void *addr; >> +    ssize_t n = 0, cur; >>       fd = open("/proc/self/exe", O_RDONLY); >>       if (!ASSERT_OK_FD(fd, "Open /proc/self/exe\n")) >> @@ -52,16 +52,6 @@ static int initialize_file_contents(void) >>       /* page-align base file address */ >>       addr = (void *)((unsigned long)addr & ~(page_sz - 1)); >> -    /* >> -     * Page out range 0..512K, use 0..256K for positive tests and >> -     * 256K..512K for negative tests expecting page faults >> -     */ >> -    for (off = 0; off < sizeof(file_contents) * 2; off += page_sz) { >> -        if (!ASSERT_OK(madvise(addr + off, page_sz, MADV_PAGEOUT), >> -                   "madvise pageout")) >> -            return errno; >> -    } >> - >>       return 0; >>   } >> @@ -90,6 +80,14 @@ static void run_test(const char *prog_name) >>       if (!ASSERT_OK(err, "file_reader__load")) >>           goto cleanup; >> +    /* >> +     * Page out range 0..512K, use 0..256K for positive tests and >> +     * 256K..512K for negative tests expecting page faults >> +     */ >> +    if (!ASSERT_OK(madvise(addr, sizeof(file_contents) * 2, >> MADV_PAGEOUT), >> +               "madvise pageout")) >> +        goto cleanup; >> + >>       err = file_reader__attach(skel); >>       if (!ASSERT_OK(err, "file_reader__attach")) >>           goto cleanup; >