From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f173.google.com (mail-lb0-f173.google.com [209.85.217.173]) by kanga.kvack.org (Postfix) with ESMTP id 744246B0035 for ; Wed, 21 May 2014 05:38:15 -0400 (EDT) Received: by mail-lb0-f173.google.com with SMTP id 10so1373040lbg.32 for ; Wed, 21 May 2014 02:38:14 -0700 (PDT) Received: from mail-la0-x230.google.com (mail-la0-x230.google.com [2a00:1450:4010:c03::230]) by mx.google.com with ESMTPS id ky5si19557100lab.32.2014.05.21.02.38.13 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 21 May 2014 02:38:13 -0700 (PDT) Received: by mail-la0-f48.google.com with SMTP id mc6so1348845lab.21 for ; Wed, 21 May 2014 02:38:13 -0700 (PDT) Subject: [PATCH] tools/vm/page-types.c: catch sigbus if raced with truncate From: Konstantin Khlebnikov Date: Wed, 21 May 2014 13:38:07 +0400 Message-ID: <20140521093807.24256.22521.stgit@zurg> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , Naoya Horiguchi Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Recently added page-cache dumping is known to be a little bit racy. But after race with truncate it just dies due to unhandled SIGBUS when it tries to poke pages beyond the new end of file. This patch adds handler for SIGBUS which skips the rest of the file. Signed-off-by: Konstantin Khlebnikov Cc: Naoya Horiguchi --- tools/vm/page-types.c | 35 ++++++++++++++++++++++++++++++++--- 1 file changed, 32 insertions(+), 3 deletions(-) diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c index 05654f5..c4d6d2e 100644 --- a/tools/vm/page-types.c +++ b/tools/vm/page-types.c @@ -32,6 +32,8 @@ #include #include #include +#include +#include #include #include #include @@ -824,21 +826,38 @@ static void show_file(const char *name, const struct stat *st) atime, now - st->st_atime); } +static sigjmp_buf sigbus_jmp; + +static void * volatile sigbus_addr; + +static void sigbus_handler(int sig, siginfo_t *info, void *ucontex) +{ + (void)sig; + (void)ucontex; + sigbus_addr = info ? info->si_addr : NULL; + siglongjmp(sigbus_jmp, 1); +} + +static struct sigaction sigbus_action = { + .sa_sigaction = sigbus_handler, + .sa_flags = SA_SIGINFO, +}; + static void walk_file(const char *name, const struct stat *st) { uint8_t vec[PAGEMAP_BATCH]; uint64_t buf[PAGEMAP_BATCH], flags; unsigned long nr_pages, pfn, i; + off_t off, end = st->st_size; int fd; - off_t off; ssize_t len; void *ptr; int first = 1; fd = checked_open(name, O_RDONLY|O_NOATIME|O_NOFOLLOW); - for (off = 0; off < st->st_size; off += len) { - nr_pages = (st->st_size - off + page_size - 1) / page_size; + for (off = 0; off < end; off += len) { + nr_pages = (end - off + page_size - 1) / page_size; if (nr_pages > PAGEMAP_BATCH) nr_pages = PAGEMAP_BATCH; len = nr_pages * page_size; @@ -855,11 +874,19 @@ static void walk_file(const char *name, const struct stat *st) if (madvise(ptr, len, MADV_RANDOM)) fatal("madvice failed: %s", name); + if (sigsetjmp(sigbus_jmp, 1)) { + end = off + sigbus_addr ? sigbus_addr - ptr : 0; + fprintf(stderr, "got sigbus at offset %lld: %s\n", + (long long)end, name); + goto got_sigbus; + } + /* populate ptes */ for (i = 0; i < nr_pages ; i++) { if (vec[i] & 1) (void)*(volatile int *)(ptr + i * page_size); } +got_sigbus: /* turn off harvesting reference bits */ if (madvise(ptr, len, MADV_SEQUENTIAL)) @@ -910,6 +937,7 @@ static void walk_page_cache(void) kpageflags_fd = checked_open(PROC_KPAGEFLAGS, O_RDONLY); pagemap_fd = checked_open("/proc/self/pagemap", O_RDONLY); + sigaction(SIGBUS, &sigbus_action, NULL); if (stat(opt_file, &st)) fatal("stat failed: %s\n", opt_file); @@ -925,6 +953,7 @@ static void walk_page_cache(void) close(kpageflags_fd); close(pagemap_fd); + signal(SIGBUS, SIG_DFL); } static void parse_file(const char *name) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org