Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v12 22/22] selftests/vm: Fix deadlock in protection_keys.c
To:     Ram Pai <linuxram@us.ibm.com>, 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 <dave.hansen@intel.com>
Message-ID: <0c82a148-3f10-66f4-a7d7-cace557ff038@intel.com>
Date:   Fri, 16 Mar 2018 15:34:52 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.6.0
MIME-Version: 1.0
In-Reply-To: <1519264541-7621-23-git-send-email-linuxram@us.ibm.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 02/21/2018 05:55 PM, Ram Pai wrote:
> From: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
> 
> 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 <dave.hansen@intel.com>