From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965855AbeEIRSy (ORCPT ); Wed, 9 May 2018 13:18:54 -0400 Received: from mga12.intel.com ([192.55.52.136]:63856 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965240AbeEIRSv (ORCPT ); Wed, 9 May 2018 13:18:51 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.49,382,1520924400"; d="scan'208";a="52900932" Subject: [PATCH 04/13] x86/pkeys/selftests: Avoid printf-in-signal deadlocks To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Dave Hansen , linuxram@us.ibm.com, tglx@linutronix.de, dave.hansen@intel.com, mpe@ellerman.id.au, mingo@kernel.org, akpm@linux-foundation.org, shuah@kernel.org From: Dave Hansen Date: Wed, 09 May 2018 10:13:44 -0700 References: <20180509171336.76636D88@viggo.jf.intel.com> In-Reply-To: <20180509171336.76636D88@viggo.jf.intel.com> Message-Id: <20180509171344.C53FD2F3@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen printf() and friends are unusable in signal handlers. They deadlock. The pkey selftest does not do any normal printing in signal handlers, only extra debugging. So, just print the format string so we get *some* output when debugging. Signed-off-by: Dave Hansen Cc: Ram Pai Cc: Thomas Gleixner Cc: Dave Hansen Cc: Michael Ellermen Cc: Ingo Molnar Cc: Andrew Morton Cc: Shuah Khan --- b/tools/testing/selftests/x86/pkey-helpers.h | 20 ++++++++------------ 1 file changed, 8 insertions(+), 12 deletions(-) diff -puN tools/testing/selftests/x86/pkey-helpers.h~pkeys-selftests-avoid-print-in-signal-deadlocks tools/testing/selftests/x86/pkey-helpers.h --- a/tools/testing/selftests/x86/pkey-helpers.h~pkeys-selftests-avoid-print-in-signal-deadlocks 2018-05-09 09:20:19.738698404 -0700 +++ b/tools/testing/selftests/x86/pkey-helpers.h 2018-05-09 09:20:19.742698404 -0700 @@ -26,30 +26,26 @@ static inline void sigsafe_printf(const { va_list ap; - va_start(ap, format); if (!dprint_in_signal) { + va_start(ap, format); vprintf(format, ap); + va_end(ap); } else { int ret; - int len = vsnprintf(dprint_in_signal_buffer, - DPRINT_IN_SIGNAL_BUF_SIZE, - format, ap); /* - * len is amount that would have been printed, - * but actual write is truncated at BUF_SIZE. + * No printf() functions are signal-safe. + * They deadlock easily. Write the format + * string to get some output, even if + * incomplete. */ - if (len > DPRINT_IN_SIGNAL_BUF_SIZE) - len = DPRINT_IN_SIGNAL_BUF_SIZE; - ret = write(1, dprint_in_signal_buffer, len); + ret = write(1, format, strlen(format)); if (ret < 0) - abort(); + exit(1); } - va_end(ap); } #define dprintf_level(level, args...) do { \ if (level <= DEBUG_LEVEL) \ sigsafe_printf(args); \ - fflush(NULL); \ } while (0) #define dprintf0(args...) dprintf_level(0, args) #define dprintf1(args...) dprintf_level(1, args) _