On Mon, Apr 20, 2026 at 03:46:37PM +0200, 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 <[email protected]>
nit typo in the subject a -> as Acked-by: Jiri Olsa <[email protected]> jirka > --- > .../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; > -- > 2.53.0 >
