From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x227XJrTh4KtG1DYe/2a4JXBzExySGtIfDZC5Eyi9nUt6JJ0gcnbbrjwXT1/XurkhWT6QJ8eT ARC-Seal: i=1; a=rsa-sha256; t=1516647268; cv=none; d=google.com; s=arc-20160816; b=cm88r2Wa13ng8UTNKkwWbF3RmVu0DQHgd/og6bBGvlHpspfpayMxVMg62XRHu5uDsm O7Txzbj9MAOFmBLjYQAUV7gySME0wfMyTqOnuBlf1sKeIWozjNZWbX3VkZoEsuMc8UjR /AnTgzm3QjqUlQSCgk2ijFQWD854pg7q1j91kBCZt3MP3UZl4fEZRivKREQwDdxj53TN Ph1TiyE3S1SL1FJtY/A23jGkc4ZUlzbWFLu6xXFDfh78Q4+HOj8Ae0tx8jsI+7nUGsgC UMhxm+t+0PRSAe/2Yo3PfRBzRuPtMUIQrrq1735/7//Y+jlFL13C0B9vY2JKnRqD+tJN YNqw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:references:in-reply-to:message-id:date :subject:cc:to:from:dkim-signature:arc-authentication-results; bh=80/nTAFHXj91xwynBb9Y6OS+erhCLQ0MULFuFxltAv4=; b=bY28QT/HfW3eJxYVunsoLYLI6oTtjlfrORWoygJSiA+84jXUFlE+tAqbIsqQT1JoGX ChFaTIvxb6pqmIFN/zG95cahAjmnUoTCHecJbY0q8nCkObY8oXrPIKJU9qWy2YTcIBdp ZItOZCm46f6WQkGIsEbwCfV0qed/4cuX4V8Igm65DuSVuzEwtuUQ0O7OIVrXOamkJn+Q P9gNljE1t7IHJ/r6oAJJtgnf8e6+AS/b/9OffioEH8lCErXnXSPVOUSEaa+NWxwvWnJA AJ8ZUTm9NfdWyCoJN/5QkqtEPxvY4bMj1kB7XCt99xYQOk/Pq3cm/0v6Vi6xLux2xKC2 rGZw== ARC-Authentication-Results: i=1; mx.google.com; dkim=neutral (body hash did not verify) header.i=@gmail.com header.s=20161025 header.b=fTJH28Gs; spf=pass (google.com: best guess record for domain of linux-kselftest-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kselftest-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=ibm.com Authentication-Results: mx.google.com; dkim=neutral (body hash did not verify) header.i=@gmail.com header.s=20161025 header.b=fTJH28Gs; spf=pass (google.com: best guess record for domain of linux-kselftest-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kselftest-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=ibm.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751618AbeAVSx7 (ORCPT ); Mon, 22 Jan 2018 13:53:59 -0500 Received: from mail-qt0-f196.google.com ([209.85.216.196]:35379 "EHLO mail-qt0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751571AbeAVSxz (ORCPT ); Mon, 22 Jan 2018 13:53:55 -0500 From: Ram Pai To: shuahkh@osg.samsung.com, linux-kselftest@vger.kernel.org Cc: mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, akpm@linux-foundation.org, dave.hansen@intel.com, benh@kernel.crashing.org, paulus@samba.org, khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com, bsingharora@gmail.com, hbabu@us.ibm.com, mhocko@kernel.org, bauerman@linux.vnet.ibm.com, ebiederm@xmission.com, linuxram@us.ibm.com, arnd@arndb.de Subject: [PATCH v10 22/24] selftests/vm: Fix deadlock in protection_keys.c Date: Mon, 22 Jan 2018 10:52:15 -0800 Message-Id: <1516647137-11174-23-git-send-email-linuxram@us.ibm.com> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1516647137-11174-1-git-send-email-linuxram@us.ibm.com> References: <1516647137-11174-1-git-send-email-linuxram@us.ibm.com> Sender: linux-kselftest-owner@vger.kernel.org X-Mailing-List: linux-kselftest@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590319926366893372?= X-GMAIL-MSGID: =?utf-8?q?1590319926366893372?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Thiago Jung Bauermann The sig_chld() handler calls dprintf2() taking care of setting dprint_in_signal so that sigsafe_printf() won't call printf(). Unfortunately, this precaution is is negated by dprintf_level(), which has a call to fflush(). This function acquires a lock, which means that if the signal interrupts an ongoing fflush() the process will deadlock. At least on powerpc this is easy to trigger, resulting in the following backtrace when attaching to the frozen process: (gdb) bt #0 0x00007fff9f96c7d8 in __lll_lock_wait_private () from /lib64/power8/libc.so.6 #1 0x00007fff9f8cba4c in _IO_flush_all_lockp () from /lib64/power8/libc.so.6 #2 0x00007fff9f8cbd1c in __GI__IO_flush_all () from /lib64/power8/libc.so.6 #3 0x00007fff9f8b7424 in fflush () from /lib64/power8/libc.so.6 #4 0x00000000100504f8 in sig_chld (x=17) at protection_keys.c:283 #5 #6 0x00007fff9f8cb8ac in _IO_flush_all_lockp () from /lib64/power8/libc.so.6 #7 0x00007fff9f8cbd1c in __GI__IO_flush_all () from /lib64/power8/libc.so.6 #8 0x00007fff9f8b7424 in fflush () from /lib64/power8/libc.so.6 #9 0x0000000010050b50 in pkey_get (pkey=7, flags=0) at protection_keys.c:379 #10 0x0000000010050dc0 in pkey_disable_set (pkey=7, flags=2) at protection_keys.c:423 #11 0x0000000010051414 in pkey_write_deny (pkey=7) at protection_keys.c:486 #12 0x00000000100556bc in test_ptrace_of_child (ptr=0x7fff9f7f0000, pkey=7) at protection_keys.c:1288 #13 0x0000000010055f60 in run_tests_once () at protection_keys.c:1414 #14 0x00000000100561a4 in main () at protection_keys.c:1459 The fix is to refrain from calling fflush() when inside a signal handler. The output may not be as pretty but at least the testcase will be able to move on. Signed-off-by: Ram Pai Signed-off-by: Thiago Jung Bauermann tools/testing/selftests/vm/pkey-helpers.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- tools/testing/selftests/vm/pkey-helpers.h | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/tools/testing/selftests/vm/pkey-helpers.h b/tools/testing/selftests/vm/pkey-helpers.h index 9d06b4a..965cfcd 100644 --- a/tools/testing/selftests/vm/pkey-helpers.h +++ b/tools/testing/selftests/vm/pkey-helpers.h @@ -131,7 +131,8 @@ static inline void sigsafe_printf(const char *format, ...) #define dprintf_level(level, args...) do { \ if (level <= DEBUG_LEVEL) \ sigsafe_printf(args); \ - fflush(NULL); \ + if (!dprint_in_signal) \ + fflush(NULL); \ } while (0) #define dprintf0(args...) dprintf_level(0, args) #define dprintf1(args...) dprintf_level(1, args) -- 1.7.1