From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4030dg2nvGzDr2b for ; Sat, 17 Mar 2018 09:35:03 +1100 (AEDT) Subject: Re: [PATCH v12 22/22] selftests/vm: Fix deadlock in protection_keys.c To: Ram Pai , shuahkh@osg.samsung.com, linux-kselftest@vger.kernel.org References: <1519264541-7621-1-git-send-email-linuxram@us.ibm.com> <1519264541-7621-23-git-send-email-linuxram@us.ibm.com> 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, 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, arnd@arndb.de From: Dave Hansen Message-ID: <0c82a148-3f10-66f4-a7d7-cace557ff038@intel.com> Date: Fri, 16 Mar 2018 15:34:52 -0700 MIME-Version: 1.0 In-Reply-To: <1519264541-7621-23-git-send-email-linuxram@us.ibm.com> Content-Type: text/plain; charset=utf-8 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 02/21/2018 05:55 PM, Ram Pai wrote: > 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: Ugh, yeah, I've run into this too. Acked-by: Dave Hansen