From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DFDEDC433FE for ; Thu, 27 Jan 2022 21:30:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344343AbiA0VaM (ORCPT ); Thu, 27 Jan 2022 16:30:12 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35414 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239644AbiA0VaL (ORCPT ); Thu, 27 Jan 2022 16:30:11 -0500 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DAC96C06173B for ; Thu, 27 Jan 2022 13:30:10 -0800 (PST) Received: by mail-yb1-xb4a.google.com with SMTP id e13-20020a25e70d000000b00615e9bc9a3cso8344194ybh.22 for ; Thu, 27 Jan 2022 13:30:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:message-id:mime-version:subject:from:to:cc; bh=B95/GPrHL3ehKM8Rm7wgzd+5Hfg8Ho8he70Zk+Aj96g=; b=M5puYGiqOpDDdPdrv13u0tkUyLBdm15VQzzeJXFp1chap+jbhRRo7I0rcuDDzOxSjl 3cL1m1qJNnLu9bKjOOptxas/2MITDJh5flskv42B0oepTyfabrKYJivvMGrjamvONs0o Qrp5dU++Y9TmLDmL1qqyxl2wXgca71IVhnAQvvQb48T9g4gG6YCElFD5FkRSnnJzLDvS xIEhtyAqcRpzfHhld5Bocs3GKyaFh5Vqx7Os2A0xBH2lm+GKomBuuLeSTJC2qf4A+AT0 KV5fWQZ3ZSDQlIhD+C+2bjXZhTDzuRUY1yzudUK4UlrkmcAjFmoexk1kiQDNW+fKh5Jr wu4g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=B95/GPrHL3ehKM8Rm7wgzd+5Hfg8Ho8he70Zk+Aj96g=; b=QuBniKTdfCY665lWfK4dOD2nD6wh/ElVnmB9iNz6oFZ6Jure88WsmgVXWYQjXQiOMv VfHjS6wK0dQLf2cxRQGL+9GxyxPO1d1mBmVMn1AC821EzdRRv5ZdS57drfmF8B72EY6H OP9pRCYRl/oVg65xDUkYwUmDIyDbrylIaVa0piiPodJkVT1bxTWp4B7EuglY2ZJsOWKF pKYqNNqm08skR5doA2kinCeKsbtUxgEcSFs4gY6UEWhwRP2taAYKNyq5Pqnc0GI+dtWI lnDIgvN8DQRUpOcJbCiEDB+5vUG1kq+MgVmulfCrNlIY3xpW88Ep5EDyUhHCt6F+byxH wKKQ== X-Gm-Message-State: AOAM530T2sqhT06cQAnZ8K7JzSlWQbh6BDysk0nq4qm9gq28IaMRBZ6L LzUesMOKY2ZGkUfSNnAaPZN/N8pNrCT8jLTyaLmz X-Google-Smtp-Source: ABdhPJz90vY8X1LcSRxAHAGv97T1CuywIIOQnBUF6s3pyOyCzGLxlxEu75zq+m942M4ZUYKJt/fKtHHa0YX0ApbvC3o+ X-Received: from ajr0.svl.corp.google.com ([2620:15c:2cd:203:c864:1e56:28bc:526b]) (user=axelrasmussen job=sendgmr) by 2002:a81:3dd7:: with SMTP id k206mr1ywa.56.1643319008177; Thu, 27 Jan 2022 13:30:08 -0800 (PST) Date: Thu, 27 Jan 2022 13:29:51 -0800 Message-Id: <20220127212951.3604667-1-axelrasmussen@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.35.0.rc2.247.g8bbb082509-goog Subject: [PATCH] pidfd: fix test failure due to stack overflow on some arches From: Axel Rasmussen To: Christian Brauner , Shuah Khan Cc: "Zach O'Keefe" , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Axel Rasmussen Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When running the pidfd_fdinfo_test on arm64, it fails for me. After some digging, the reason is that the child exits due to SIGBUS, because it overflows the 1024 byte stack we've reserved for it. To fix the issue, increase the stack size to 8192 bytes (this number is somewhat arbitrary, and was arrived at through experimentation -- I kept doubling until the failure no longer occurred). Also, let's make the issue easier to debug. wait_for_pid() returns an ambiguous value: it may return -1 in all of these cases: 1. waitpid() itself returned -1 2. waitpid() returned success, but we found !WIFEXITED(status). 3. The child process exited, but it did so with a -1 exit code. There's no way for the caller to tell the difference. So, at least log which occurred, so the test runner can debug things. While debugging this, I found that we had !WIFEXITED(), because the child exited due to a signal. This seems like a reasonably common case, so also print out whether or not we have WIFSIGNALED(), and the associated WTERMSIG() (if any). This lets us see the SIGBUS I'm fixing clearly when it occurs. Finally, I'm suspicious of allocating the child's stack on our stack. man clone(2) suggests that the correct way to do this is with mmap(), and in particular by setting MAP_STACK. So, switch to doing it that way instead. Signed-off-by: Axel Rasmussen --- tools/testing/selftests/pidfd/pidfd.h | 13 ++++++++--- .../selftests/pidfd/pidfd_fdinfo_test.c | 22 +++++++++++++++---- 2 files changed, 28 insertions(+), 7 deletions(-) diff --git a/tools/testing/selftests/pidfd/pidfd.h b/tools/testing/selftests/pidfd/pidfd.h index 01f8d3c0cf2c..6922d6417e1c 100644 --- a/tools/testing/selftests/pidfd/pidfd.h +++ b/tools/testing/selftests/pidfd/pidfd.h @@ -68,7 +68,7 @@ #define PIDFD_SKIP 3 #define PIDFD_XFAIL 4 -int wait_for_pid(pid_t pid) +static inline int wait_for_pid(pid_t pid) { int status, ret; @@ -78,13 +78,20 @@ int wait_for_pid(pid_t pid) if (errno == EINTR) goto again; + ksft_print_msg("waitpid returned -1, errno=%d\n", errno); return -1; } - if (!WIFEXITED(status)) + if (!WIFEXITED(status)) { + ksft_print_msg( + "waitpid !WIFEXITED, WIFSIGNALED=%d, WTERMSIG=%d\n", + WIFSIGNALED(status), WTERMSIG(status)); return -1; + } - return WEXITSTATUS(status); + ret = WEXITSTATUS(status); + ksft_print_msg("waitpid WEXITSTATUS=%d\n", ret); + return ret; } static inline int sys_pidfd_open(pid_t pid, unsigned int flags) diff --git a/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c index 22558524f71c..3fd8e903118f 100644 --- a/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c +++ b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c @@ -12,6 +12,7 @@ #include #include #include +#include #include "pidfd.h" #include "../kselftest.h" @@ -80,7 +81,10 @@ static inline int error_check(struct error *err, const char *test_name) return err->code; } +#define CHILD_STACK_SIZE 8192 + struct child { + char *stack; pid_t pid; int fd; }; @@ -89,17 +93,22 @@ static struct child clone_newns(int (*fn)(void *), void *args, struct error *err) { static int flags = CLONE_PIDFD | CLONE_NEWPID | CLONE_NEWNS | SIGCHLD; - size_t stack_size = 1024; - char *stack[1024] = { 0 }; struct child ret; if (!(flags & CLONE_NEWUSER) && geteuid() != 0) flags |= CLONE_NEWUSER; + ret.stack = mmap(NULL, CHILD_STACK_SIZE, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0); + if (ret.stack == MAP_FAILED) { + error_set(err, -1, "mmap of stack failed (errno %d)", errno); + return ret; + } + #ifdef __ia64__ - ret.pid = __clone2(fn, stack, stack_size, flags, args, &ret.fd); + ret.pid = __clone2(fn, ret.stack, CHILD_STACK_SIZE, flags, args, &ret.fd); #else - ret.pid = clone(fn, stack + stack_size, flags, args, &ret.fd); + ret.pid = clone(fn, ret.stack + CHILD_STACK_SIZE, flags, args, &ret.fd); #endif if (ret.pid < 0) { @@ -129,6 +138,11 @@ static inline int child_join(struct child *child, struct error *err) else if (r > 0) error_set(err, r, "child %d reported: %d", child->pid, r); + if (munmap(child->stack, CHILD_STACK_SIZE)) { + error_set(err, -1, "munmap of child stack failed (errno %d)", errno); + r = -1; + } + return r; } -- 2.35.0.rc2.247.g8bbb082509-goog