From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f69.google.com (mail-pl0-f69.google.com [209.85.160.69]) by kanga.kvack.org (Postfix) with ESMTP id 235306B0540 for ; Wed, 9 May 2018 13:18:52 -0400 (EDT) Received: by mail-pl0-f69.google.com with SMTP id t5-v6so4066207ply.13 for ; Wed, 09 May 2018 10:18:52 -0700 (PDT) Received: from mga05.intel.com (mga05.intel.com. [192.55.52.43]) by mx.google.com with ESMTPS id o9-v6si15900013pgn.199.2018.05.09.10.18.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 May 2018 10:18:50 -0700 (PDT) Subject: [PATCH 04/13] x86/pkeys/selftests: Avoid printf-in-signal deadlocks 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: owner-linux-mm@kvack.org List-ID: 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 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) _